Previous Page Table of Contents Next Page


13. Management measures

Terence I. Walker
Marine and Freshwater Systems Institute
PO Box 114, Queenscliff
Victoria 3225, Australia
<Terry.Walker@dpi.vic.gov.au>

13.1 INTRODUCTION

Fisheries management can be viewed as an assemblage of restrictions on fishing or, alternatively, viewed with positive connotations as bestowing use rights for harvesting fish to an individual, company, group or community. With use rights go the obligation to apply those rights in a responsible manner.

In allocating fishing rights, clear objectives need to be set for a fishery. These objectives will relate to sustainable use of the resource, provision of food and other products, economic return to the community, welfare of fishing communities, biodiversity conservation and maintenance of the structure and function of ecosystems. The mix of objectives for any fishery will inevitably change with community attitudes and with stage of development depending on whether the fishery is evolving from a traditional to an artisan fishery or from an artisan to an industrial fishery. Compromises are inevitable in successfully addressing competing social, political, legal, economic and biological objectives.

Fisheries impacting populations of chondrichthyans (sharks, rays and chimaeras) require careful management. Where excess fishing capacity occurs, mechanisms need to be established to reduce capacity to levels commensurate with the biological productivities of the harvested species to ensure sustainable and rational use of the resources. Similarly, where bycatch species are depleted or threatened, then steps need to be taken to manage and, if necessary, provide special protection to those species for biodiversity conservation. Critical habitats need to be protected and, where affected by fishing or other human activities, restored. At a broader level, trophic interactions and the effects of fishing need to be understood and if necessary managed to ensure that the resilience of ecosystems are not impaired.

The present Section briefly characterizes fisheries that affect populations of chondrichthyan species and identifies those features of their biology that can cause their populations to be sensitive to the effects of fishing. It outlines the elements of fishing mortality and how these need to be understood when considering gear restrictions or constructing more environmentally benign gear for conservation and management of this group of animals. The Section develops a method for rapid assessment of risk to identifying species most in need of precautionary management. It also describes the outcomes of complex political processes culminating in the International Plan of Action for the Conservation and Management of Sharks and describes the jurisdictional and institutional frameworks required for administration, consultation, monitoring, research, assessment and surveillance in fisheries. The tools of fisheries management are presented here in the framework of use rights and restrictions imposed through technical measures. For chondrichthyan animals, special attention is required to protect newborn and young juveniles and maternal animals for species that have nursery, pupping and mating grounds, or migration lanes. The advantages of prescribing in law the form in which these animals can be landed are also discussed.

The terminology adopted mostly follows the Code of Conduct for Responsible Fisheries developed under the auspices of the Food and Agriculture Organization of the United Nations (FAO, 1995). The term “catch susceptibility”is adapted from the scientific literature (Stobutzki, Miller and Brewer, 2001; Stobutzki et al., 2002) for the purpose of the present chapter. In addition, a distinction is made between the terms “fishing area closure”and “marine protected area”. This distinction is made to distinguish area closures designed to meet fishery-management objectives of ensuring sustainable use of a resource, biodiversity conservation, amelioration of ecological impacts of fishing and reduction of interference with other human activities (e.g. shipping and recreation) from area closures designed to meet other community objectives. The concept of a fishing area closure, which is an essential management tool for managing animals of low productivity such as chondrichthyans, is extended to promote the concept of “regional fisheries management”.

13.2 FISHERIES, BIOLOGY AND ASSESSMENT OF CHONDRICHTHYAN SPECIES

13.2.1 Fisheries affecting chondrichthyan species

The harvest of animals for products from shark and other chondrichthyan species pre-dates recorded history. Every part of these animals has been used for some purpose. Depending on the region of the world, shark meat is an important food consumed fresh, dried, salted or smoked. The demand for fins of sharks has grown rapidly in recent years such that they are now among the world's most expensive fishery products. Similarly, the demand is rising for shark cartilage and other products for medicinal purposes. In some fisheries, only the meat is retained, while the rest of the animal is discarded. In other fisheries, only the fins, or liver or skin is retained; few fisheries utilize all parts of the animals.

The number of shark species targeted is small compared with the number of species of teleosts and many of the invertebrate phyla harvested. This has resulted in a lack of studies of sharks and inappropriate stock assessment techniques being applied to these animals. Most of the shark catch is taken by fishers targeting teleost species, which results in most of the catch being reported as unidentified shark or mixed fish or not reported at all. In addition, sharks can be difficult to identify to species level, particularly given the need to behead and eviscerate sharks at sea to reduce spoilage rates of the meat and the fishers”preference to remove fins at sea. Taxonomic problems need to be resolved, particularly for batoids, before effective monitoring, research and management can be achieved. This lack of species identification for catches and lack of information on fishing effort means basic data for fishery stock assessment are currently available for only a few species (Walker, 1998).

Although the overall number of species harvested is relatively small, sharks are captured with a wide variety of fishing gear and vessels. Sharks are mostly taken by gillnet, hook or trawl in industrial and artisanal fisheries. Small amounts are taken in traditional and recreational fisheries, including game fishers and divers, and by bather protection programs using beach gillnets and drumline fishing. There are several fisheries directed at one or a small number of species of sharks, but most sharks are taken in multispecies fisheries where the fishers tend to target more highly valued teleosts. In some fisheries, part or the entire shark catch is discarded. Shark fisheries can be classified as “coastal hook and gillnet fisheries”, “demersal trawl bycatch fisheries”, “deepwater bycatch fisheries”, “pelagic bycatch fisheries”(primarily bycatch in tuna longline and purse seine fisheries) and “freshwater fisheries”(FAO, 2000).

Coastal hook and gillnet fisheries operate in regions of the continental shelf. Construction of the fishing gear depends on topography of the fishing grounds and on the available species mix of shark, chimaerid and teleost species. Much of the artisanal catch is taken by bottom-set longlines and by bottom-set gillnets, mostly constructed of monofilament webbing with some constructed of multifilament webbing. These gears take a variety of shark species and teleost species. In regions of narrow continental shelves where deep waters off the continental shelf are readily accessible, or in regions of broader continental shelves, the artisanal fleet uses surface-set longlines and driftnets to target pelagic sharks (FAO, 2000).

In demersal trawl bycatch fisheries, demersal trawl fisheries reduce stocks of dogfishes (Squaliformes), angel sharks (Squatiniformes), rays (batoids) and chimaeras (holocephalans). As in the high seas fisheries, much of the trawl bycatch of sharks and rays is discarded dead and often not reported. Fishery-independent surveys in several parts of the world show that many species of these groups have exhibited marked declines in abundance.

In deepwater bycatch fisheries, like many of the teleost species studied from the deeper and colder waters of the continental slopes, the deepwater dogfishes (notably the genera Centrophorus, Centroscymnus, Etmopterus, Dalatias and Deania) have particularly low productivity. The continental slopes are usually steep and the total area of associated seabed is small compared with the areas of the continental shelves and the abyssal plains of the oceans. As some species of dogfish are confined to particular depth-ranges on these slopes, the total area occupied by some of these species is small. Expansion of demersal trawl fisheries into progressively deeper water to target dogfish and high valued teleosts on the continental slopes in some regions of the world is placing several species at high risk of severe depletion. Already demersal trawling occurs on the continental slopes at depths exceeding 1000 m. Part of the catch is targeted or is bycatch taken by gillnets and hooks (Walker, 1998).

In pelagic shark bycatch fisheries, longline, purse seine and driftnet fisheries targeting tunas and tuna-like species on the high seas and in the Exclusive Economic Zones, through bilateral access agreements, take significant bycatch of sharks. Blue shark (Prionace glauca) is the main species caught and other species caught widely in lower quantities include Isurus oxyrinchus, Alopias supercilious, Carcharhinus falciformis, Carcharhinus longimanus and Lamna nasus (Bonfil, 1994; FAO, 2000).

In freshwater fisheries, shark species occurring in freshwater habitats are among some of the most threatened species. There are several reasons why these species are more vulnerable than those inhabiting marine waters. The amount of freshwater in rivers and lakes is small compared with the amount of seawater on Earth. The tropical rivers and lakes where freshwater species occur are mostly in developing countries with large and expanding human populations. These areas are more accessible to exploitation than marine waters. Freshwater habitats are also less stable than marine habitats in terms of water temperature, dissolved oxygen, clarity and water flow and these factors are gradually being changed through deforestation. Contamination of the water with toxicants from mining and agriculture, physical modifications to the waterways through dam construction and irrigation and inevitable changes to the flora and fauna in freshwater habitats are likely to alter them beyond the tolerance of some shark species. Several species of sharks and rays have declined such that they are now extremely rare (Compagno, 1984; Compagno and Cook, 1995).

13.2.2 Biological characterization of chondrichthyan species

Populations of shark and other chondrichthyan species tend to have lower reproductive rates and lower natural-mortality rates than populations of teleost and invertebrate species. Consequently, for many chondrichthyan species, only a small proportion of the population can be removed annually if the catches and populations are to remain sustainable. Such populations are said to have low biological productivity.

Harvested populations of these animals therefore require careful management and monitoring. Managers need to take a more precautionary approach to the management of fisheries that take sharks than they might to the management of fisheries based on teleost or invertebrate species. Late maturity, low fecundity and parturition cycles often exceeding one year provide for close stock-recruitment relationships, with relatively little inter-annual variability in response to environmental variation and for long stock recovery periods in response to overfishing.

There are directed fisheries for sharks in various parts of the world, but most species of shark are captured in multispecies fisheries directed at more productive and usually more highly valued teleost species. Harvest strategies designed to optimise economic and social benefits from these multispecies fisheries inevitably deplete the less productive shark and other chondrichthyan species unless strategies for reducing the catch of the less productive species can be developed and implemented. As fishing effort increases, characteristic and predictable changes occur in the fish assemblages. The number of large animals decline or disappear from the assemblage and are replaced by smaller animals. This results in a gradual drift towards shorter-lived, faster-growing species. This is accompanied by an initial increase and later a decrease in the number of species in the exploitable population although the number of fish actually appearing in the catch can increase to a maximum level.

In multispecies fisheries where the main target species are teleosts, sharks landed as nontarget species (byproduct) or caught and discarded (bycatch) might require “special management”to prevent severe depletion. Some species of shark are apex predators and naturally have comparatively small population sizes. Whereas some species have wide geographic distributions, others have restricted ranges falling within the full range of a fishery or the range of other anthropogenic influences. Some species have complex spatial stock structures, with critical habitats such as nursery, parturition and mating areas and migration lanes, which might need special protection (Walker, 1998).

The magnitude of change in many of the world's fisheries has not been well appreciated because most of the change occurred during the early developmental stages of the fisheries before surveys began and subsequent fisheries management has only been effective at stabilising fish stocks at low levels. Recent meta-analysis of large survey data sets from throughout the world indicates industrialized fisheries typically reduce community biomass by 80% during the first 15 years of exploitation, which inevitably leads to marked changes in coastal ecosystem structure and function. The analyses suggest that the global ocean has lost more than 90% of large predatory fish (Myers and Worm, 2003). This paints a bleak picture for the world's fish fauna and marine ecosystems in general, but given the biological characteristics of the chondrichthyan fauna, it can be expected that this group of animals is among the most severely affected. This is exacerbated in the open ocean for large predatory sharks, which, along with tunas, billfishes and sea turtles, tend to aggregate at distinct diversity hotspots associated with coral reefs, shelf breaks and sea mounts. These animals appear to be particularly vulnerable to targeting in latitudes 20–30° N and S where tropical and temperate species overlap (Worms et al., 2003).

The failure to manage for sustainability at rational levels is primarily due to socio-political pressure for short-term gain in harvests and due to intrinsic uncertainty in predicting the harvest that can cause stock collapse. There is, nevertheless, a growing awareness of the need for a more holistic approach by considering multispecies interactions and influences of the physical environment to achieve sustainability through adaptive management (Botsford, Catilla and Peterson, 1997).

This requires an ecosystem approach to fisheries management, which integrates information from a wide range of disciplines and applies mathematical models to synthesize multiple processes at a wide range of spatial and temporal scales. Greater use of fishing area closures and moratoria can reduce risks to sustainability through application of the precautionary principle. Harvest refuges effectively protect a proportion of the exploited population and reduce uncertain assumptions about relationships between fishing effort, catch and biomass (Botsford, Catilla and Peterson, 1997). Exposing an entire population to exploitation without a sound understanding of the dynamics of the fishery can risk depletion, whereas fishing area closures can serve as a hedge against inevitable uncertainty (Lauck et al., 1998). However, such areas provide insufficient protection alone because they are not isolated from all critical impacts; scales of fundamental processes, such as population replenishment, are much larger than the areas they can encompass. Fishing area closures need to be complemented by other management and conservation measures outside the closures (Allison, Lubchenco and Carr, 1998).

An ecosystem approach to fisheries management requires management over broad regions and across fisheries and away from single-species and single-fishery management that characterizes past and present practices. The approach involves monitoring all species affected by fishing and requires better understanding of the dynamics of fish movement and species interactions through food chains. Whereas complex models and comprehensive long-term monitoring data sets are required to reduce uncertainty, it is essential in the short-term to develop rapid assessment methods based on simpler data sets and judgement that can provide for interim management of species and ecosystems at risk.

13.2.3 Fishing mortality

In fishery models, fishing mortality rate for a harvested population is usually expressed as the product of the two quantities: fishing effort and catchability. Fishing effort can be quantified as the number of fishing vessels in a fleet, a measure of the amount of fishing gear deployed, amount of fishing time, or some other variable that is a mix of these variables. “Catchability”is the proportion of the exploited population taken by one unit of fishing effort and has a value in the range 0–1 for any age or size of fish. It is the product of three parameters, each of which also has a value in the range 0–1. The three parameters comprising catchability are “availability”, “encounterability”and “selectivity”; i.e.:

catchability = availability × encounterability × selectivity

Availability is the proportion of the habitat area of a population fished by the fleet. A population with a habitat area extending well beyond the range of the fishing fleet has a low availability value. Conversely, a population with a habitat area that falls entirely inside the range of the fishery has a high availability value of one, unless parts of the habitat area are inaccessible to the fishing fleet.

Encounterability is the proportion of that part of the population available to fishery encountered by one unit of fishing effort. For any species, encounterability depends on construction of the fishing gear and on the biological characteristics of that species. Pelagic and semipelagic species that actively swim in the water column are more likely than less active species to encounter passive gears such as gillnets or longlines with baited hooks. These actively swimming species therefore have a higher encounterability to these gears than the less active species. For mobile gears such as demersal trawl, bottom-dwelling, sluggish species, such as angel sharks (Squatiniformes) and batoids have a higher probability of capture and therefore higher encounterability than the more powerful swimming species, such as the whaler and hammerhead sharks (Carcharhiniformes) and mackerel sharks (Lamniformes). Sixgill and sevengill sharks (Hexanchiformes), sawsharks (Pristiophoriformes), dogfishes (Squaliformes), catsharks, wobbegong and carpet sharks (Orectolobiformes) and horn sharks (Heterodontiformes) probably exhibit intermediate trawl encounterability.

“Selectivity”is the proportion of the animals encountering the fishing gear that is captured by the fishing gear. For any fishing gear, selectivity gives rise to a range of complex dynamics that relate features of the fishing gear to size of the fish captured. Selectivity by trawl nets for size of chondrichthyan animals is not well understood and hook-size selectivity for size of fish is weak. For gillnets, however, sharks of different sizes are not equally vulnerable to capture. Small animals swim through gillnets but become progressively more vulnerable to capture as they grow. After reaching the length of maximum vulnerability they then become progressively less vulnerable with further growth as they deflect from the meshes of the nets (Kirkwood and Walker, 1986). These size selectivity effects are stronger for fusiform-shaped sharks than for more dorsoventrally-flattened species or for species with protruding structures such the heads of hammerhead sharks, the rostral teeth of pristiophorid sawsharks and pristid sawfishes and the dorsal spines of squalid and heterodontid sharks and chimaerids. When captured by gillnet or hook, fast swimming species, dependent on ram-jet ventilation of their gills for respiration tend to die more quickly than bottom-dwelling species when caught. Bottom-dwelling species with spiracles to aid gill ventilation are better able to pass water over their gills after capture by gillnets and can struggle vigorously to either escape or become more tightly enmeshed in the gear. Species that can struggle vigorously after capture in gillnets tend to have narrower selectivity ranges than species that struggle less. Hence, for some species, careful regulation of mesh-size can be used to ensure that the sharks captured are large enough to avoid growth overfishing and small enough to facilitate escapement of large breeding animals to avoid recruitment overfishing (Walker, 1998).

The concept of catchability is usually applied to target and byproduct species where most of the animals captured are retained. So as to broaden the concept to include bycatch, the term “catch susceptibility”(Stobutzki et al., 2002) and the term “post-capture mortality”are adopted here to describe the survival of that part of the catch that is released. The parameters catch susceptibility and post-capture mortality both have values in the range 0–1 and are related to each other and to catchability by the equation:

catch susceptibility = catchability × post-capture mortality

which can hence be further expanded to provide the equation:

catch susceptibility = availability × encounterability × selectivity × post-capture mortality

Post-capture mortality is the proportion of fish that die as a result of being caught in, or encountering the fishing gear. Fish of target and byproduct species that are mostly retained have a post-capture mortality value approaching one. This can be less if some are discarded because of their size or breeding condition. Post-capture mortality for discarded species can vary markedly. In addition to handling by fishers, the fishing gear and biological characteristics can contribute to various kinds of mortality referred to as unaccounted fishing mortality or collateral mortality. Dead sharks not tightly enmeshed can drop out of gillnets and contribute to unaccounted fishing mortality through drop-out mortality. Sharks eaten by other fish or mammals after capture in the gear contribute to unaccounted fishing mortality through predation mortality. Dead sharks, either partly or totally decomposed or eaten by invertebrates and vertebrates when fishing gear is left in the water for extended periods, also contribute to unaccounted fishing mortality. Lost gillnets contribute to unaccounted fishing mortality through ghost fishing mortality until they are rolled into a ball by tidal flow. Postcapture mortality from normal handling by fishers is low for heterodontid and orectolobid sharks but high for carcharhinids.

13.2.4 Rapid assessment for evaluation of risk

Stock assessment of chondrichthyan species that incorporates time series of catch and indices of relative abundance, includes biological parameters and accounts for fishing gear selectivity has been undertaken for only a few species, such as Mustelus antarcticus (Walker, 1994; Walker, 1998) and Galeorhinus galeus harvested of southern Australia. The assessments of G.galeus also incorporate spatiality (Punt et al., 2000) and evaluation of risk in a Bayesian framework (Punt et al., 2000; Punt and Walker, 1998). Such assessments require large data sets from long-term fishery monitoring and extensive biological and gear selectivity studies (see Section 10). Because of their comparatively low biological productivity and, for many species, their high catch susceptibility, most chondrichthyan species require management action long before sufficient data are available to undertake a full stock assessment. It is therefore necessary to apply rapid assessment techniques for evaluation of risk from the effects of fishing.

A rapid assessment approach for evaluating risk to chondrichthyan species was applied to species caught as bycatch in a tropical prawn fishery in northern Australia (Stobutzki et al., 2002). This method ranks the relative sustainability of each species on the basis of its “susceptibility”and “recovery”(Stobutzki, Miller and Brewer, 2001; Stobutzki et al., 2002), which are assessed on the basis of the biological attributes of the species. A similar approach is proposed here for sharks and other chondrichthyans, but the approach alters the terminology and the method of quantification of the various parameters used to be more compatible with more comprehensive fishery assessment methods.

The method proposed here provides a framework for considering a species”ecological risk, risk of depletion or risk of extinction. For this method, the terms “catch susceptibility”and “biological productivity”are used in place of susceptibility and recovery to represent parameters associated with fishing mortality and population growth, respectively.

Species of high biological productivity can be viewed as having rapid population turnover, whereas species of low biological productivity can be viewed as having slow population turnover. For an unexploited population to remain in equilibrium, there has to be a balance between the natural mortality rate reducing numbers and the reproductive rate increasing numbers. Otherwise, over time, if the reproductive rate exceeded the natural mortality rate, the population would grow to infinity; conversely, if the natural mortality rate exceeded the reproductive rate, the population would go extinct. Low reproductive rate and low natural mortality rate are associated with low biological productivity, whereas high reproductive rate and high natural mortality rate are associated with high biological productivity. It follows, therefore, that either reproductive rate or natural mortality rate can serve as a proxy for biological productivity for rapid assessment.

Other expressions of biological productivity include the “intrinsic rate of population growth”parameter formulated variously in biomass dynamics models (Schaefer, 1957; Schnute, 1985), demographic models (Lotka, 1922) and various adaptations of these models for sharks (Au and Smith, 1997; Xiao and Walker, 2000). Using a particular formulation of a demographic model to allow for density-dependent change in natural mortality (Au and Smith, 1997), Smith, Au and Show (1998) classed 26 Pacific shark species on the basis of the “intrinsic rate of population growth”(referred to by the authors as “rebound potential”) . In addition, intrinsic rate of population growth is related to inter-generation period and reproductive output per generation (Heron, 1972). Application of biomass dynamics models requires time series of catch and relative abundance data and demographic analysis combines available parameter estimates for natural mortality rate and reproduction. Required information on chondrichthyan reproduction for a population for this purpose includes the maternity ogive (proportion of the female population contributing to annual recruitment expressed as a function of length or age), fecundity expressed as a function of maternal length or age and sex ratio of progeny. If the maternity ogive and fecundity are expressed as a function of length, then the relationship between length and age is also required for the application of demographic models.

Using the natural mortality rate as a proxy for biological productivity requires some caution, as the natural mortality rate is likely to be density-dependent and age-dependent. Also, fishing is likely to remove the oldest animals from the population and reduce the maximum age detected in a sample of animals collected for ageing purposes. Notwithstanding these potential biases, rough estimates of natural mortality or maximum age can be used for broad categorization of risk. The instantaneous mortality rate, M, can be approximately related to maximum age, tmax, by the equation ln (0.01) = -M tmax where 0.01 represents survival of 1% of the animals reaching maximum age (Hoenig, 1983). Because natural mortality rate is much higher for the young age-classes than the older age-classes, as demonstrated from modelling shark populations (Punt and Walker, 1998; Walker, 1994), this equation is reformulated here for application to chondrichthyans by considering only that part of the population of age greater than 2 years. Assuming that mortality is constant for all age-classes, calculations of instantaneous total mortality rate of 1% for 2-year-old animals to survive to ages 8, 16 and 24 years are 0.77, 0.33 and 0.21, respectively. If total mortality is divided evenly between natural mortality and fishing mortality, a condition sometimes assumed for a population in equilibrium to produce the maximum sustainable yield (Au and Smith, 1997; Thompson, 1992), natural mortality rates for 2-year-old animals surviving to these ages approximate to 0.38, 0.16 and 0.10, respectively. These values are used as a basis for arbitrary categorization of chondrichthyan species risk (Table 13.1). For example, based on published instantaneous natural mortality rates, Galeorhinus galeus (Punt and Walker, 1998; Smith, Au and Show, 1998), Carcharodon carcharias, Carcharias taurus, Carcharhinus plumbeus and C. obscurus (Smith, Au and Show, 1998) can be classed at high risk. Similarly Mustelus antarcticus (Walker, 1994), M. californicus, M. henlei and Sphyrna tiburo (Smith, Au and Show, 1998) can be classed at medium risk and Rhizoprionodon terraenovae can be classed at low risk (Smith, Au and Show, 1998).

TABLE 13.1
Values of various parameters for three arbitraty categories of risk.

ParameterValues for three arbitrary categories of risk
 Low (L)Medium (M)High (H)
Total mortality (y-1)>0.760.32–0.760.00–0.31
Natural mortality (y-1)>0.380.16–0.380.00–0.15
Maximum age (y)0–89–16>16
Availability0.00–0.330.34–0.660.67–1.00
Encounterability0.00–0.330.34–0.660.67–1.00
Selectivity0.00–0.330.34–0.660.67–1.00
Post-capture mortality0.00–0.330.34–0.660.67–1.00
Catch susceptibility0.00–0.330.34–0.660.67–1.00

Catch susceptibility and each of its four components (availability, encounterability, selectivity and post-capture mortality) can also be arbitrarily divided into three categories of risk. This is achieved here by evenly dividing the possible value range of 0.00–1.00 into the three ranges 0.00–0.33, 0.34–0.66 and 0.67–1.00, designated low (L), medium (M) and high (H), respectively. For example, in each fishing method adopted in the fisheries of south-eastern Australia, it is possible to categorize encounterability, selectivity and post-capture mortality into one of the three categories on the basis of chondrichthyan taxonomic order (Table 13.2) by considering the animals”biological characteristics. This means that the only parameter to be determined for any particular species is “availability”, which for rapid assessment can be estimated as the ratio of the area fished within the spatial range of that species divided by the entire area inhabited by the species. By adopting the upper limit values for the three ranges of 0.33, 0.66 and 1.00 for low, medium and high risk, respectively, then catch susceptibility can also be categorized as low, medium or high risk. For example for a fishing method where availability is low, encounterability is high, selectivity is high and post-capture mortality is high, then “catch susceptibility”is low. This is calculated as catch susceptibility = 0.33 × 1.00 × 1.00 × 1.00 = 0.33 (i.e. catch susceptibility = LHHH = L).

TABLE 13.2
Catch susceptibility of chondrichthyan animals to demersal fishing gear.

Catch susceptibility is defined as ‘availability’ × ‘encounterability' × ‘selectivity' × ‘post-capture mortality'; ‘availability' is the ratio of area of range of species divided by the area of the range of the fishery; ‘catch susceptibility', ‘availability', ‘vulnerability', ‘selectivity', and ‘discard post-harvest mortality' all have values ranging 0–1, for risk assessment these are categorised as L (low, O.00-O.33 ), M (medium, 0.34-O.66), and H (high, 0.67–1.00).

Taxonomic orderCommon nameEncounterabilitySelectivityDiscard post-harvest mortality
Trawl/ seineGillnetHookTrap/potTrawl/ seineGillnet 6–6 ½ inHookTrap/potTrawl/seineGillnet 6–6 ½ inHookTrap/pot
Pelagic and semipelagic species
CarcharhiniformesWhaler & hammerhead sharksLLLLHMHLHHMH
LamniformesMackerel & thresher sharksLLMLHMHLHHMH
Demersal species
CarcharhiniformesWhaler & hammerhead sharksLHHLHMHLHMLH
SquatiniformesAngel sharksHLLLHLHMMLLL
PristiophoriformesSawsharksMHMLHHHMHHLM
SqualiformesDogfishesMHHLHLHHMMLL
HexanchiformesSixgill & sevengill sharksLHHLHMHHHHMH
OrectolobiformesCatsharks, wobbegongs, carpetMHHMHMHHMLLL
HeterodontiformesHorn sharksMHMLHMHHMLLL
PristiformesSawfishesHLLLHHHHHLLL
RhinobatiformesShovelnose and guitar raysHLLLHLHHHLLL
TorpediniformesElectric raysHLLLHLHHHLLL
RajiformesSkatesHLLLHLHHHLLL
MyliobatiformesEagle & devil rays and stingraysHLLLHLHHHLLL
HoloceplialiformesChimaerasMLLLHMHHHHML

Footnote: The values presented in this table are based on species found in south-eastern Australia, but they should be applicable to most regions of the world, except ‘selectivity’ of gillnets presented here is for 6–6½ inch mesh-size which is likely to vary with region depending on size of animals for each species in the region.

13.3 FRAMEWORKS FOR FISHERIES MANAGEMENT

13.3.1 International developments

Growing widespread concern during the past decade about expanding fisheries for sharks and for the potential impacts of fishing on their populations and those of rays and chimaeras led to initiatives to implement better management of these animals. During the mid-1990s, submissions were presented to the Convention for International Trade in Endangered Species of Wild Fauna and Flora (CITES) seeking restrictions on the trade of products from sharks as a means of controlling the harvest of these animals. In response to requests from its members, the Food and Agricultural Organization of the United Nations (FAO) subsequently initiated a process that led to development of the International Plan of Action for the Conservation and Management of Sharks (IPOA-Sharks). The IPOA-Sharks was endorsed by the FAO Committee of Fisheries (COFI) during 15–19 February 1999. The IPOA-Sharks provides guidelines to member nations for development of National Plans of Action for the Conservation and Management of Sharks (NPOA-Sharks) and for coordination of shark management at global, regional and sub-regional levels under the auspices of FAO. The IPOA-Sharks supplements the Code of Conduct for Responsible Fisheries and defines “sharks”to include sharks, rays and chimaeras.

Through the IPOA-Sharks and other international developments, the scope of fisheries management for these animals is expanding beyond the focus of sustainable use of the resource to take account of the need for biodiversity conservation and maintenance of ecosystem structure and function. There is also growing emphasis on bycatch reduction and on ethical issues associated with full utilization of dead sharks and the handling and processing of these animals (FAO, 2000).

13.3.2 Jurisdictional and institutional frameworks

Fisheries management presupposes a minimum set of institutional arrangements and recurrent activities at local, sub-national, national, regional and global levels. Entities engaged in fisheries management require appropriate policy and legal and institutional frameworks to adopt measures for the long-term conservation and sustainable use of shark fishery resources. Conservation and management measures need to be based on the best scientific evidence available. Effective coordination of implementation of fisheries management at a national level through development of shark plans and ongoing shark assessments requires a structure, a definition of roles, agreed processes and mobilization of resources. All relevant fishing sectors, fishing communities, non-government organizations and other interested parties should be consulted as part of the decision-making process. Creation of public awareness of the need for the management of shark resources and participation in the management process by those affected should be promoted.

To be effective, management of fisheries has to be concerned with whole stock units over the entire area of distribution of the species harvested. The best scientific evidence available should be used to determine the area of distribution of the resource and the area through which a fish in the stock migrates during its life cycle. Where a stock falls entirely within the Exclusive Economic Zone (EEZ) of a single nation then that resource can be managed under the single jurisdiction of that nation. Where a stock straddles in the EEZs of more than one nation and, or, the high seas, complex jurisdictional arrangements are required. Shared or trans-boundary straddling-stocks need to be managed through bilateral and multilateral arrangements or Regional Fisheries Management Organizations (RFMOs) (FAO, 2000).

All nations are free to harvest fish in the high seas and regulation is beyond the control of any individual country. Straddling and highly migratory fish stocks maybe managed cooperatively the Agreement for the Implementation of the United Nations Convention on the Law of the Sea of 10 December 1982 Relating to the Convention and Management of Straddling Fish Stocks and Highly Migratory Fish Stocks, more briefly termed the UN Fish Stocks Agreement. Ratification of the Agreement by nations provides rights to, and obligations on those nations and prescribes fisheries management principles for the long-term conservation and sustainable use of straddling and highly migratory fish stocks. The Agreement provides a framework for cooperation between fishing nations, including through RFMOs. It also provides rights to member nations of RFMOs to board and inspect member fishing vessels on the high seas to check compliance with regionally agreed conservation and management measures. Nations signing the Agreement accept the principles of the Agreement. The UN Fish Stocks Agreement depends on “flag State responsibility”, which is a principle of international law. The national law applying to a vessel on the high seas is the law of the country whose flag the vessel is entitled to carry. If there is any infringement of rules, the flag State of the vessel concerned is responsible for investigating and taking appropriate enforcement action.

13.4 USE RIGHTS

13.4.1 Benefits of use rights

Granting use rights bestows property rights whereby an individual, company, or defined group or community can own fish after the fish have been captured. Once captured the fish become private property. Before they are captured, the fish are private property only if the water body holding the fish is private property. Within a country's EEZ, fish in the water are usually deemed the property of the citizens of that country and said to be state property. Nevertheless, a state can legislate to privatize fish in the water for harvesting rights and thereby grant ownership to an individual, company, or defined group or community. Where the fish in the water are owned in common by a defined group or community, the fish are said to be their common property. For example, where a government legislates to bestow ownership of fish in a specific body of water to people traditionally using that fish resource, the fish in the water become the common property of those people. However, the fish of an entire nation are often referred to as common property. Here the group or community is defined as including all citizens of a nation; the term common property here maybe equated to state property (Charles, 2002).

Through fisheries management, use rights can be implemented under private property, state property or common property. In addition, the UN Fish Stocks Agreement (Article 10) provides a facility to prescribe use rights in waters outside the EEZs of nations on the high seas where the fish in the water are deemed “non-property”(Charles, 2002). Fishery managers need to ensure that no vessel is allowed to capture sharks or take sharks as bycatch unless authorized in a manner consistent with international law for the high seas or in conformity with national or sub-national legislation within areas of national or sub-national jurisdiction.

The FAO World Fisheries Conference in Rome during 1983 recognized that open access to non-managed fisheries resulted in competition for limited resources, overcapitalization of the industry and depletion of stocks. It was considered that fishers should have clearly-defined fishing rights and that catches should not exceed the productivity of the resource. One approach to allocate rights for the capacity to fish is through input controls such as licence allocation. Another approach is to allocate rights for specified shares of the resource through output controls in the form of catch quotas (King, 1995).

13.4.2 Territorial use rights

Rights can be assigned to individuals or communities to fish in certain locations based on longstanding tradition of use (customary usage). This approach is variously termed territorial use rights in fishing (TURFs) and customary marine tenure (CMT). A feature of these systems is the local solution of usage issues. Many fishing communities informally regulate their fishing effort, based on their observations of fish abundance and their interpretation of their indicators of abundance over time (Charles, 2002).

Territorial management is highly effective where it is supervised by the fishing community itself or by its elected leaders. Many TURF and CMT systems have declined as traditional fisheries commercialize. Nevertheless, several countries of Oceania, such as Solomon Islands, Fiji and Samoa, have moved to re-establish these systems. Customary fishing ground boundaries based on oral claims are being formalized in legislation (Charles, 2002). Japan, for example, has integrated ancient local systems of management into fisheries planning at all levels of local, regional and national government (Pinkerton, 2002). A challenge for countries is to support traditional approaches to management and to integrate them into regional and national management systems through co-management agreements. There is evidence of customary usage of sharks and rays in Canada, northern Australia (Last and Stevens, 1994), Solomon Islands (Sant and Hayes, 1996) and New Zealand (Francis, 1998). However, there are no examples where territorial use rights have been formally granted specifically for the harvest of chondrichthyan animals in recognition of traditional usage.

13.4.3 Limited entry

Limited entry is a common management tool whereby the management agency issues a limited number of licences to take fish. This creates a use right to participate in a particular fishery. Licence limitation is the restriction of fishing rights to those fishers, fishing units or fishing vessels licenced in a fishery.

Several types of fishing licences are used for fisheries management throughout the world. A “personal licence”authorizes a particular fisher to deploy fishing gear for catching fish, but requires the licenced fisher to be present at the site of fishing operations. A “vessel licence”authorizes a particular vessel to deploy fishing gear for catching fish, but requires operations to be made from the licenced vessel. A “fishery access licence”authorizes the holder, or a person nominated by the holder, to deploy fishing gear for catching fish from any nominated vessel. A “gear licence”authorizes the use of a particular item of fishing gear for catching fish by the holder, or a person nominated by the holder, from any nominated vessel. Special conditions or endorsements on such licences can be used to nominate one or more fisheries, species, gears, catch levels or effort levels that are authorized.

Licences are either non-transferable or transferable. Non-transferable licences are auctioned or issued at the discretion of the licensing authority through a Minister of State. Development of merit criteria as guidelines for issuing non-transferable licences by licensing authorities are usually criticized as discriminatory. Allocation of non-transferable licences according to merit inevitably leads to dissatisfaction and pressure from holders to make the licences transferable. Transferable licences are exchanged by mutual financial agreement between the seller and buyer, usually within guidelines prescribed by the licensing authority. Once transferable, licences acquire a value related to earnings that might be acquired from possessing the licence. Debts associated with the purchase of transferable licences create an incentive to increase the catch to service the loans, which create a need to reduce the number of licences or entitlements associated with each licence. If there is the need to reduce the number of licences in a fishery, the licensing authority can withhold non-transferable licences, but has to buy back transferable licences from licence holders at market price.

Annual licence fees collected by the licensing authority can be used to recoup management, surveillance, research and fishery monitoring costs and collect a resource rent on behalf of the community. Personal licences can be effective in artisanal and recreational fisheries, but fishery access or vessel licences are favored in industrial fisheries where costly assets are required and there is a need to exchange fishing masters or skippers on a vessel to ensure its economic viability. All four types of licence have been variously applied in fisheries either targeting sharks or taking sharks as byproduct or bycatch.

Limited entry caps the number of operators in a fishery, but is rarely sufficient to manage a fishery. Once licence limitation is implemented, improved skill of the operators and technological innovation inevitably increase the fishing power of the vessels in the fleet. Limited entry is best implemented during the early phase of the development of a fishery, before the catching power of the fleet is excessive. It is difficult to reduce the number of licences once there is over-capacity in the fleet. Whereas limited entry is a reasonable mechanism for assigning use rights, it must be implemented as part of a portfolio of management actions.

13.4.4 Quantitative input rights (effort rights)

Input controls designed to limit or reduce fishing mortality require some form of restrictive licensing, which limits the number of fishing vessels engaged in a particular fishery and some measure for limiting the fishing effort of the licenced vessels. Where over-fishing occurs and the fleet is too large, there is a need to reduce the number of licenced vessels or reduce the fishing efficiency of the vessels. Further, where licence limitation is established, incremental technological advances in vessel and fishing gear design and improvements in fish-finding equipment and navigation aids are likely to cause the effective fishing capacity of a fleet to increase with time. In addition, if the licences are transferable and acquire progressively higher value, economic forces will cause inactive vessels with their associated latent effort to become active and increase the total effort applied by the entire fleet. Hence, with any input control system, increasing efficiency and increasing effort create an ongoing need to reduce the number of vessels or efficiency of each vessel. Over-capacity of a fleet can be reduced in several ways: removing vessels, reducing fishing time of the vessels, limiting the amount or size of gear that a vessel can carry, or reducing efficiency of fishing effort.

Removing vessels from the fleet requires rescinding licences. This involves removing the rights from some vessels to operate in a fleet. One system applied for this purpose is referred to as a Buy-Back Scheme or Decommissioning Scheme where funds are made available by government, the industry itself or some other stakeholder group to purchase licences as a means to removing vessels from the fishery. A feature with these schemes is that the least efficient operators have the highest economic incentive to sell their licences. Whereas this improves the overall economic efficiency of the fleet, it can result in a large number of vessels being removed with little change in overall fishing mortality.

Reducing vessels”fishing time can be implemented by imposing limits on the number of days or times of the day vessels can operate. Extended closed seasons, closed days of the week, or closed times of day are unpopular with fishers as it reduces flexibility and creates incentives to operate under adverse weather conditions. Closed days of the week are seen as inequitable as it effects greatest on larger vessels that undertake extended periods at sea. Closed periods disrupt market supply of fish and employment patterns.

Fishing capacity of a fleet can be restricted by limiting the size of vessel and engine power and thereby restrict the ability of vessels to tow fishing gear such as demersal trawls. For most other fishing methods, however, the relationship between the size of the gear and the size of the vessel or power of the engine is not so clear. Nevertheless, fishing capacity of a fleet can be restricted by limiting the size of vessels and thereby restricting the number of fishing days by weather conditions. This can cause problems of safety for fishers if there are strong economic incentives to operate under hazardous conditions.

Fishing gear can be limited in type, size and number. Gillnets can be restricted by controlling the length and height of the nets, the mesh-size of the webbing and hanging ratio for the construction of the nets. Longlines can be restricted by controlling the length (or volume) of mainline and the number of hooks that can be used during each operation. Restrictions can also be placed on hook size and presence or absence of a wire trace between the hook and the snood and on the use of automatic baiting and setting machines. Trawl nets can be limited to a maximum length of headline.

Gear regulations tend to restrict the efficiency and cost of catching fish for each operator. Gear restrictions are often implemented where there are the social objectives of providing employment and food to a large number of traditional and artisan fishers. Hence, gear restrictions are minimized where there is the economic management goal for reducing the number of operators and improving economic efficiency, but can be adopted as a means to maintain fishing communities and promote equity of incomes among participants (Pope, 2002).

Some of the benefits of limits on the quantity of fixed gear used, such as gillnets, can be offset by the gear being in the water for extended periods. Legislating for vessels not to leave the gear unattended discourages the practice of returning to port while the gear remains set at sea. This practice leads to cryptic fishing mortality from predation mortality and ghost fishing mortality if the nets are lost.

Meeting the biological objective of reducing fishing mortality by reducing vessel efficiency is incompatible with the economic objective of improving economic efficiency of the fleet. Similarly, meeting the biological objective by reducing vessel numbers is incompatible with the social objective of providing employment for fishing communities.

There are many general vessel and fishing regulations that apply across fisheries, but few have been implemented specifically for chondrichthyan species. Within the European Union, every country has agreed to a maximum gross tonnage of vessels and maximum engine power. The limits are set for each fishery, fishery sector and, in some cases, fish stock (Pawson and Vince, 1999).

During the late 1980s and the 1990s, a complex system of quantitative rights was adopted for the shark fishery of southern Australia. Depending on historic catches by a vessel, vessel licences were endorsed to use various length of gillnets. These gear holdings were not transferable except for a short period when a small proportion of the licences could be amalgamated to allow for an increase in gear holdings. After amalgamation, the maximum gear holding was 6000 meters long, but this was subsequently reduced to 4200 meters (Walker, 1999). This type of effort rights was taken a step further in the shark fishery of Western Australia. Here time-gear units were allocated where a time-gear unit authorized the use of a particular length of gillnet for one month of the year (Simpfendorfer, 1999).

13.4.5 Quantitative output rights (catch quotas)

Limitation of catch, also referred to as output control, can take the form of a global catch quota, individual quotas as non-transferable individual quotas or individual transferable quotas (ITQs) with a total allowable catch (TAC), bag limits or trip limits.

A global catch quota, commonly referred to as a competitive TAC, is the maximum catch allowed from a resource by the entire fleet for a year or season. Under this system, individual fishers compete for catch until the fleet reaches the overall limit and the fishery is then closed. Such a system requires rapid collation of catch statistics to be effective. Individual fishers feel compelled to operate under hazardous weather conditions and to invest in vessel capacity and gear to attain a competitive edge. This can result in progressively shorter seasons, which disrupt employment patterns and market supplies.

Bag limits are a simpler form of regulation where the number of animals a person or vessel can retain is limited. Bag limits are usually applied on a daily basis for recreational fishers where an individual is permitted to land up to a specified catch weight or a prescribed number of carcasses. Limiting the number of carcasses can create an incentive to retain the largest animals and discard small animals, which might be dead and hence contribute to cryptic fishing mortality.

Trip limits may be applied on a trip or daily basis for fishers who do not hold a licence to operate in the fishery. Trip limits may be designed to avoid wastage by allowing non-licenced operators to land byproduct catch. However, the trip limit needs to be sufficiently low so as not to encourage targeting by non-licenced operators. Trip limits may be also applied in a fishery to discourage “derby fishing”and to spread the take of a quota over a long period of time.

Individual non-transferable quotas are are prescribed for each operator's catch, which is usually fixed as a specified proportion of the TAC. This avoids the competitive element, but does not allow an operator to increase catch by personal choice.

Individual Transferable Quotas (ITQs) provide each operator with a prescribed catch of one or more units of catch. The ITQs can be traded freely, or traded between specified operators. Operators can hold one or more ITQs, depending on the number they choose to buy. By prescribing an ITQ or non-transferable quota as a proportion of the TAC, the catch allowed under each ITQ varies depending on the TAC, which can be set annually or for some other period. The facility to trade ITQs allows less efficient operators to sell all or part of their quota to more efficient operators at the market price of the quota. A substantial enforcement effort is required to ensure that individual quotas are not exceeded. Individual catch quotas create an incentive to under-report catches and a temptation to sell illegal catch to black market buyers.

In addition, management by individual quotas can encourage operators to discard that part of the catch that potentially receives a low price (e.g. damaged, small or large animals) and replace them with animals that would receive a higher price, a practice referred to as high grading.

TACs for some species of fish are expressed as the number of fish, but they are usually expressed in terms of weight. Although they should ideally relate to the catch, for administrative convenience they are limits on landings. Components of TACs are often used as a basis for resource allocation between different user groups, such as between recreational users and commercial users or between sectors or regions of the commercial users. This also occurs in internationally shared fisheries where allocations are negotiated between countries.

Various types of TACs are administered for shark resources. For management of the United States Atlantic Shark Fishery, 39 species of sharks are categorized into four groups: “large coastal”, “small coastal”, “pelagic”and “prohibited”for the commercial sectors of the fishery. Apart from the prohibited group, each group has a separate TAC, reviewed periodically. In the absence of limited entry in the fishery, the commercial catches have regularly exceeded the TACs. In addition, there is a commercial trip limit of 4000 pounds for the large coastal group and a recreational fishing bag limit of two sharks per boat per day plus two Atlantic sharpnose sharks (Rhizoprionodon terraenovae) per person per day or trip (Branstetter, 1999). New Zealand and Australia have set TACs for individual species of shark and have an ITQ system of management (Francis, 1998; Walker, 1999).

13.5 TECHNICAL MEASURES

13.5.1 Regulation of fishing gear

Ideal fishing gear achieves many things simultaneously. It is efficient at capturing target species while avoiding small fishes so as to minimize growth overfishing and avoiding large breeding animals to minimize recruitment overfishing of the species. It has negligible direct or indirect impact on bycatch species, habitats and substrates and it causes minimal damage to animals captured and in no way diminishes the food quality of the animals caught.

Regulation of fishing gear can be used to control fishing mortality, impacts on habitats and ecosystems and food quality of fish retained. Regulation of fishing gear should not be used as a way of controlling the fishing effort component of fishing mortality, but rather as a way of controlling the catch susceptibility component of fishing mortality. This can be achieved by variously controlling one or more of the four components of catch susceptibility -availability, encounterability, selectivity and post-capture mortality. Availability can be controlled through fishing area closures to the use of specific gears, whereas encounterability, selectivity and post-capture mortality can be controlled or regulated through the manner of gear construction or the way it is used.

Fishing gears maybe classified as passive or active. This classification is based on the behaviour of the target species in relation to the gear. Passive gears include gillnets, trammel nets, longlines, handlines, jigs, droplines, troll lines, pots and fish traps. Active gears include spears, harpoons, dredges, demersal trawls, mid-water trawls, Danish seine nets, Scottish seine nets, beach seines and purse seines. Table 13.3 provides an evaluation of different fishing gears for selectivity and ecosystem effects of fishing. The values presented are from evaluation across many fisheries, but specific values for a particular fishery, particularly as it might relate to chondrichthyan species, can be altered depending on regulation of the fishing gear (Bjordal, 2002).

TABLE 13.3
Estimates of ecosystem effects of fishing for different fishing gears.

Ranking is a scale from 1 (non favourable) to 10 (highly favourable) for different ecosystem related factors. The ecosystem effect index is the mean of the other seven factors (reproduced from (Bjordal, 2002).

Fishing gearSize selectionSpecies selectionBycatch mortalityGhost fishingHabitat effectsEnergy efficiencyCatch qualityEcosystem effect index
Gillnets84517855.4
Trammel nets23537854.7
Handlining446109997.3
Longlining65698887.1
Pots77938897.3
Traps55889997.6
Spear, harpoon8951010898.4
Pelagic trawl47399486.3
Demersal trawl44692264.7
Beam trawl44692164.6
Shrimp trawl11794264.3
Seine net55694586.0
Purse seine-7599887.7
Beach seine22596996.1

Fishery managers need to ensure that fishing methods and practices in a fishery are consistent with the FAO Code of Conduct for Responsible Fisheries. Those methods that are not should be phased out and replaced with acceptable methods and practices (FAO, 1995, 2000).

The type of fishing gear used and the species of shark taken as bycatch determines which techniques and equipment are appropriate for minimizing bycatch. For trawl nets, there is evidence that catches of sharks have been reduced when fitted with turtle exclusion devices, suggesting there might be advantages investigating alternative devices designed specifically to exclude sharks. Also, there is scope to reduce bycatch of sharks in gillnets by regulating mesh-size and possibly the breaking strain of the webbing filaments. Many species of sharks remain alive on hooks for extended periods and can be released alive. There might be scope to improve survival of sharks by prohibiting the use of wire traces used to attach hooks to the snoods on a longline and by regulating for reduced breaking strains of the snoods. Wire traces reduce the probability of hooks being bitten off the snoods by sharks. Regulation of hook size may provide a means of eliminating or reducing the catch of smaller, younger individuals in a shark populations (Dowd, 2003, Musick, unpublished). Minimum mesh-sizes or square mesh panels in codends of trawl nets are widely applied, but are not intended specifically for chondrichthyan species. Selection of appropriate trawl codend mesh size and shape might have some benefit in allowing neonate and small juvenile sharks to escape.

Regulation of mesh-size is a highly effective measure for shark management. Careful selection of mid-sized mesh allows small animals to pass through the meshes and large animals, notably breeding and other mature animals, to escape (Kirkwood and Walker, 1986). Adoption of a predominantly 6-inch mesh-size during 1975 has been the key to success in sustainable use of the gummy shark (Mustelus antarcticus) stocks in Bass Strait. In this fishery, not only does the gear selectivity allow escapement of small and large animals, but the fishers operate in areas inhabited by mid-sized animals, which tend to be away from the inshore areas inhabited by pre-recruits and breeding females (Walker, 1998). In Western Australia, mesh sizes, vertical number of meshes and net length in the construction of shark gillnets are also controlled. These vary between different zones (Simpfendorfer, 1999).

13.5.2 Area and time restrictions

13.5.2.1 Protecting areas

Fishing closures involve restricting some or all methods of fishing in selected areas. Closures can be permanent, temporary, seasonal, daily or part of the day. Spatial and temporal closures are frequently applied to meet specific fishery-management objectives, but they are also used to meet other community objectives. Other objectives for closures include protecting marine, estuarine and freshwater biota, items of special cultural value, or geologic interest. In addition, areas might be set aside for specific purposes such as navigation, aquaculture or mining. The various purposes of closures have produced confusion and debate over terminology. For the purpose of this chapter, a distinction is made between closures designed to meet fisheries management objectives and closures designed to meet other community objectives. The two terms adopted are “fishing area closure”and “marine protected area”.

These terms are not meant to be mutually exclusive, but rather to provide a means for distinguishing between addressing fisheries management objectives as they relate to sustainable use, biodiversity conservation and protection of ecosystem structure and function from the effects of fishing and addressing other community objectives. The fishery manager needs the flexibility of prescribing management boundaries and varying rules between zones. At the simplest level, this might be prohibiting angling from a jetty to avoid injury to bathers. At a more complex level action might zone a region of thousands of square kilometers to meet a range of fishery and ecological objectives through a system of licensing use rights, gear restrictions and area closures across several fisheries. For example, gear restrictions across a complex of zones might be designed to provide high sustainable yields from target species of high biological productivity, while simultaneously minimizing impacts on bycatch species of low biological productivity. Where marine protected areas are proposed within broad fishing areas, an astute fishery manager will endeavor to influence the positioning of the boundaries that are compatible with fisheries objectives or at least gain some benefit for a fishery. Examples of how marine protected areas and fishing area closures can benefit sustainable use of target species and biodiversity conservation of chondrichthyan animals are presented in the following section.

13.5.2.2 Marine protected area

A marine protected area (MPA) is defined by the World Conservation Union (IUCN) as “any area of intertidal or subtidal terrain, together with its overlying water and associated flora, fauna, historical and cultural features, which has been reserved by law or other effective means to protect part or all of the enclosed environment”(Anon., 1988). An MPA can be large or small and the overall objectives for an MPA can be specific or broad. Large MPAs with broad objectives are often divided into geographically smaller zones. Depending upon the objectives, an MPA, or a zone within an MPA, might be designated for one or more uses. MPAs are usually defined based on judgement using qualitative information, as obtaining quantitative evaluation is costly and long time-series of environmental or community monitoring-data are rarely available. Selected areas are usually judged as being unique or having high conservation value. An example of a unique area declared as an MPA is the stromatolite assemblage of Shark Bay, Western Australia. Corner Inlet in Victoria, Australia, on the other hand, was declared an MPA in 1983 because it was judged to have several high conservation values. These values include the presence of international migratory birds, soft substrate biotic communities, mangrove stands and Posidonia sea grass meadows (Plummer et al., 2003). In Australia and South Africa, for example, networks of MPAs are being established to protect representative areas of a range of habitat types.

MPAs with single or multiple zones have been declared throughout the world for providing various levels of protection and for a variety of uses. A preservation zone or wilderness zone usually provides the highest level of protection through very limited access. A cultural zone is designed to provide protection to special items of cultural value and sites of historic, cultural or religious significance. These include shipwrecks, archaeological relics, submerged aboriginal middens and fossils. Zones that allow for access, but with minimal disturbance, include educational, scientific, experimental and recreation zones. An educational zone is usually a relatively safe diving or intertidal area that can be visited for training and educational purposes. In scientific zones authorized researchers can undertake the study of particular species or ecology of marine communities. Other types of zones, such as recreational or traditional fishing zones, allow for exploitative activities. A recreational zone might allow for diving and photography but no fishing, or might allow for recreational fishing activities. A traditional fishing zone recognizes traditional fishing rights of a community or group of individuals and allows for ongoing subsistence fishing.

MPAs are highly suitable for management of chondrichthyan species that aggregate where they are vulnerable to capture or disturbance by human activities (Bonifil, 1999). There are several examples from various parts of the world where these have been applied for sharks and rays. In New South Wales, Australia, the grey nurse shark (Carcharias taurus) is fully protected, but, to avoid unintentional kill in the coastal waters from longline fishing, a system of 10 sanctuary areas was established in December 2002. Each sanctuary extends 200 metres out from an island or a section of coast with buffer zones extending a further 800 metres. Fishing is prohibited and new controls on scuba diving include bans on night diving, feeding, touching, harassing or chasing sharks and on use of electronic shark repelling devices and electric scooters in these areas. In the Florida Keys National Marine Sanctuary, nurse shark (Ginglymostoma cirratum) mating aggregations at the Dry Tortuga Island group were recently given added protection by implementing a seasonal closure to boat traffic (Bonfil, 1999; Stevens 2002). The Ningaloo Reef Marine Park in northern Western Australia on the edge of the Indian Ocean provides protection to whale shark (Rhincodon typus) when these animals aggregate in this region from late March to early May. The number of divers and hours that divers and boats can approach these animals is restricted. Touching the animals or use of camera-flash lights is prohibited (Tricas et al., 1997). The Kinabatangan wildlife sanctuary in Sabah, East Malaysia includes about 27000 hectares of tropical forest and the lower reaches of the Kinabatangan River and provides some protection (although some artisanal fishers operate there) to several rare freshwater elasmobranch species. These include the river speartooth shark (Glyphis sp.), giant freshwater stingray (Himantura chaophraya) and greattooth sawfish (Pristis microdon) (Payne and Andau, 2002).

13.5.2.3 Fishing area closure

Fishing area closure is defined here as closing an area to all, or selected fishing gears for continuous or selected time periods to limit fishing mortality on all or particular length or age-classes of one or more fish species, or to reduce gear impacts on habitats or other uses. Fishing area closures can be applied to target, byproduct, or bycatch species. MPAs can also limit fishing mortality, but areas closed to meet fisheries management objectives are not normally referred to as MPAs, marine parks, reserves or sanctuaries. In MPAs, more than fishing mortality and impact of fishing gear are controlled.

Fishing area closures can be used as a fisheries management tool to meet specific fisheries objectives. One important objective is to protect aggregations of small (pre-recruit) animals to allow them to grow and thereby improve yield per recruit by avoiding growth over-fishing. Another important objective is to protect aggregations of breeding or mature animals to enhance survival of the largest animals and so produce the highest number of offspring and thereby avoid recruitment overfishing.

Fishing area closures will be used much more extensively in the future and there are several reasons why they have been applied conservatively in the past. First, fisheries managers have tended to focus attention on abundant species with high biological productivity, whereas closures are better for managing less abundant species with low biological productivity. Second, setting boundaries for closures requires extensive data sets to provide detailed information on distribution and biological condition of fish and often these data sets have not been available. Third, fishery managers have been reluctant to prescribe in law complex demarcation boundaries because they have been difficult to enforce and fishers have been often uncertain of their navigational position at sea in relation to demarcation boundaries.

There have been several developments in recent years to facilitate greater application of fishing area closures in the future. One of these developments is the growing awareness in the community that chondrichthyan species are among the least biologically productive animals and need special conservation and management attention. In addition, three important technological developments in recent years make fishing area closures a more practicable fisheries management tool. The first development is that of Geoglobal Positioning Systems (GPS), which enable the position of a vessel to be known continuously with high precision. The second development is that of Geographic Information Systems, which allow for better management, analysis and visual display of spatial data. This innovation provides a facility to better understand the spatial and temporal distributions of species and habitats and to better evaluate the significance of various areas. The third development is that of vessel monitoring systems (VMS), which overcome the need for deployment of high-cost patrol vessels. VMS allows the navigational positions of vessels at sea to be electronically monitored using satellite communication systems. As costs of VMS decline so too will the surveillance cost for effective enforcement of fishing area closures.

Two types of fishing area closures have been implemented in the shark fishery of southern Australia since the 1950s. Closure to shark longline fishing in nursery areas of school shark (Galeorhinus galeus) in the inshore waters of northern and south-eastern Tasmania were first adopted in 1954 and extended in the 1960s. In 1990, regulations were extended to included gillnets used for targeting sharks (>150 mm mesh-size) and gillnets for recreational and commercial fishing to target other species (60–70 mm mesh-size) in some of these areas. These closures were designed to prevent targeting pregnant females entering shallow waters for parturition, as well as to reduce the incidental kill of neonate and small juvenile animals (Williams and Schaap 1992). In addition, closed seasons during October or November (the months immediately prior to parturition) were adopted across the entire fishery during 1953–67. During 1994, the use of gillnets were prohibited during the period from 8 October to 22 November for the area west of the South Australia-Victoria border and during the period from 11 November to 25 December for the area east of the border. These rolling closures were designed to protect pregnant animals as they migrated from the western region of the fishery to the nursery areas in the eastern region for parturition (Walker, 1999).

Another example of a fishing area closure for sharks were the large areas closed to gillnet and longline fishing for sharks in Western Australia to protect breeding Carcharhinus obscurus and C. plumbeus (Simpfendorfer, 1999). Also, although not specifically designed for chondrichthyan species, many nations designate coastal waters for artisanal fisheries and those further offshore for industrial fleets. Though designed for social reasons, it does provide some limitation on fishing mortality in coastal waters.

The most promising approach to fisheries management is to take a more regional approach and adopt greater use of fishing area closures. There are numerous examples where fishing area closures have been applied in the past, but they have tended to be small inshore areas.

13.5.2.4 Regional fisheries management

Regional fisheries management is defined here as integrated management of a broad region of waters across species and fisheries. Management is through allocation of use rights and application of fishing area closures and other technical measures. It is designed to efficiently harvest resources in specified areas and to meet the triple goals of sustainable use with high yields, biodiversity conservation and maintenance of ecosystem resilience. Open and closed areas are selected to minimize impacts on pre-recruit and breeding and other mature animals of target species, on species of low biological productivity and on habitats, particularly critical habitats.

A regional approach to fisheries management through the judicial use of fishing area closures is required to avoid depletion of species with low biological productivity that are affected by fishing gear used to target species of high biological productivity. Maximum benefits from fishing area closures can be attained by aligning refuge areas for species of high catch susceptibility and low biological productivity (low reproductive rates and low natural mortality rates) with areas containing critical habitats and pre-recruit and breeding animals of the target species. While some trade-offs are inevitable, where practicable, the fishing area closures should not be so large that there are insufficient fishing grounds open to efficiently harvest high-valued target species to ensure high sustainable yields.

Regional fisheries management requires an exhaustive information base. Extensive data sets on monitoring distribution, abundance and fishing mortality and on critical habitats and population biology are not only required for intensive management of target species, but for all byproduct and bycatch species. The positions of the boundaries of the fishing area closures need to be flexible so they can be updated as improved information is acquired. Through improved information and an adaptive management approach, the goal is to optimize yields across species, biodiversity conservation and ecosystem maintenance.

The low biological productivity of many chondrichthyan species is likely to have a major influence on the boundaries of area closures and will provide an impetus to adopt the regional fisheries management approach. Also, species found in temperate regions tend to have lower productivity than those found in tropical regions and those found in cold deepwater on the continental slope tend to have lower biological productivity than those found in the warmer waters on the continental shelf in temperate regions. The recent depletion of the deepwater squalids and chimaerids on the continental slopes of the Earth's temperate regions, such as southern Australia (Graham, Andrew and Hodgson, 2001), has created a need to establish substantial refuge areas for these species.

Multispecies modelling tools for evaluation of alternative spatial policy options are emerging. Such models need to account for trophic interactions with important top-down impacts of predators on prey and dispersal responses of harvested species and redistribution of fishing effort in response to trophic cascades. Determination of appropriate sizes and effectiveness of closed areas are highly dependent on predator-prey relationships and movement rates of harvested species. In general, a few large closed fishing areas are likely to be more effective than a large number of small ones. Local protection can be negated by fishing effort concentrated at the boundaries of closed fishing areas or at nearby sites where the presence of prey species attracts mobile predator species from the closed areas (Walters, Pauly and Chistensen, 1999). Importantly, the perimeter-to-area ratio decreases as size of closed area increases. Closed area boundaries can be minimized by having large closed fishing areas and by placing the closed fishing areas adjacent to land or in bays and inlets (Walters, 2000).

Closure of fishing areas can have unintended consequences caused by the redistribution of effort from those areas, particularly if the fisheries are principally managed by TACs and ITQs. Whereas TACs and ITQs control the catch of quota species, which are usually target or byproduct species, they do not control bycatch species. Hence, redistributed effort from closed areas might have undesirable effects on bycatch species. A management alternative to TACs with ITQs is to adopt a total allowable effort with ITQs specified as “transferable effort quotas”(Walters and Bonfil 1999). These quotas could be allocated according to a carefully prescribed distributional pattern and would depend on VMS for control.

13.5.3 Product form

Products from sharks and other chondrichthyans, when landed, or later occur in many forms including whole animal, carcass, tissue or processed product. The carcass can be beheaded and eviscerated with skin on and fins on, beheaded and eviscerated with skin on and fins off, or beheaded and eviscerated with skin off and fins off. Tissues, body parts or product can be in the form of meat fillets, heads, jaws, head cartilage, vertebral column, powdered cartilage, skin, fins, whole livers, or liver oil.

This wide range of product forms creates difficulties identifying the species or measuring these animals when they are brought ashore. This results in ambiguity in the official catch statistics. Monitoring sex composition of the catch is not possible if the pelvic fines and claspers of males are removed. Monitoring length-frequency composition and enforcing size limits usually involves measuring partial length, which can be uncertain if all fins and the tail are removed.

Fishers should not be forced to land sharks whole, because sharks need to be gutted and gilled as soon as practicable after capture to avoid degrading the quality of the meat and other products. Species, sex and partial length of a shark can be determined ashore if sharks are beheaded and eviscerated at sea and landed in the product form as carcasses with fins, skin, claspers and, where applicable, dorsal spines attached. Leaving the head attached, with the gills removed, is an option where species identification from the carcass with fins attached is uncertain. If there is a requirement for species identification for marketing or trade purposes, field guides based on fins and other body parts will need to be prepared. There may also be advantages in establishing regulations to ensure that shark products (carcasses, meat, fins, skins, heads, vertebral columns, livers, liver oil and jaws) are clearly labelled with species name. If sharks are not required by law to be landed in a standard product form, statistics forms may require provision for reporting the product form of the sharks, in addition to reporting weight of catch. This also applies to data from landing sites, processing plants and markets and applies to trade data. All trade products should be specified by species and as frozen or dried. Without these provisions catch weights will be ambiguous.

If more than one product form occurs it is necessary to have appropriate weight conversion factors to produce a single set of standard statistics. Similarly, if it is necessary to adopt more than one standard length measurement, the data should be converted to a single standardized length, ideally total length or fork length.

To standardize the statistics for chondrichthyan species, Australia has adopted the following wording in its National Plan of Action for the Conservation and Management of Sharks (Anon., 2002).

13.5.4 Size limits

Legal size limits can be minimum or maximum sizes. They can be an effective management measure where the animals are landed from the fishing gear live and in a condition where the survival rate of released animals is high. Conversely, size limits are ineffective where the animals are landed dead or in poor condition and survival of released animals is unlikely. Hence, they are effective for many species that survive release from hooks, seine nets and fish traps, but are ineffective for species released after capture where survival rates are low.

Legal minimum sizes can be used to avoid growth overfishing, which results in the yield from a fishery is sub-optimal as many of the fish are caught when they are small and the yield from the fishery is lower than the potential yield had the animals been given time to grow and increase their size.

Legal maximum sizes can be used to avoid recruitment overfishing. This maybe useful for those species of sharks where the proportion of the females in breeding condition each year increases with size and fecundity increases with maternal size. Where reproductive rates increase with size, the contribution to recruitment is likely to be much higher for large animals than for small animals. Hence, there can be stock benefits in releasing large animals live. A legal maximum size is likely to be of higher value for females than for males.

Further, there is usually a strong correlation between mercury concentration in shark meat and shark size (Forrester, Ketchen and Wong, 1972; Walker, 1976). Where the concentration in large animals exceeds food standards, the legal maximum sizes have occasionally been used as a means of reducing the number of sharks with high mercury concentrations from reaching the consumer (Walker, 1980).

Fishers recognize the benefit of releasing undersized animals and usually endorse legal minimum sizes as they understand that sharks can be recaptured at a later and larger size. On the other hand, they are less likely to support legal maximum sizes. Large animals have a higher market value and fishers are aware of the uncertainty of survival of large released animals. It is therefore preferable to apply alternative management measures to protect large animals.

Minimum and maximum legal sizes are usually expressed in terms of length. Because most sharks are beheaded when the animals are landed, length needs to be prescribed as a partial length rather than a total length. The longest reliable partial length that can be taken from a beheaded and eviscerated carcass is from the last gill-slit to the distal end of the caudal fin. The last gill-slit closely coincides with the anterior edge of the pectoral fin, or, where the fins are removed, the cartilage from the pectoral girdle is usually intact. Where the caudal fin is removed, then the base of the caudal fin should be used.

In Australia, a legal maximum length was applied for school shark (Galeorhinus galeus) in Victoria, during 1972–85 to reduce the average mercury concentration in shark meat reaching the consumer (Walker, 1999). For a similar reason, a maximum weight of 18 kg for a trimmed carcass applies to all sharks landed in Western Australia (Simpfendorfer, 1999). Legal minimum lengths for sharks have been applied in south-eastern Australia for school shark and gummy shark since 1949 (Walker, 1999).

13.6 SPECIAL PROTECTION OF THREATENED SPECIES

Naturally rare species and species with poor conservation status may require special protection or management through such measures as a prohibition on catch, injury or interference. When this happens accidentally, consideration should be given to establishing sanctuaries through fishing area closures or MPAs.

There are no internationally agreed definitions of “threatened”or “endangered with extinction,”but some countries have adopted classifications such as “endangered,”“threatened”and “depleted”, which have legal status in their jurisdictions. The most widely accepted classification for the conservation status of chondrichthyan species is the IUCN Red List, which classifies species as “critically endangered”, “endangered”, “vulnerable”, lower risk”and “data deficient”. The first three of these are grouped as “threatened”species. Criteria for classifying species include rate of population depletion (percentage decline over three generations), overall population size and geographic area and extent of fragmentation within the distributional range of the species (Anon., 1994; Hilton-Taylor, 2000). Chondrichthyan species first appeared on the IUCN Red List in 1996 (Hudson and Mace, 1996). In 2000 when the list was last updated by the IUCN Shark Specialist Group, 40 chondrichthyan species were listed as threatened world-wide and an additional 5 species were listed within isolated local populations. More recently, 31 chondrichthyan species have been identified as becoming extinct at particular localities and one regionally extinct (Dulvy, Sadovy and Reynolds, 2003).

Some species are classed as threatened on the basis of extreme rarity. These include all river sharks (Glyphis spp.), all freshwater sawfish (Pristis spp.) and several other freshwater batoids. Others species are classified as threatened because their populations have been depleted by the effects of fishing. These include several species of angel shark (Squatina spp.) and batoid species severely impacted by trawl fisheries. Species, which have naturally small populations and have been depleted, include the whale shark (Rhincodon typus), basking shark (Cetorhinus maximus), grey nurse shark (Carcharias taurus) and white shark (Carcharodon carcharias) (Anon., in press; Camhi et al., 1998).

Various initiatives to protect endangered species have been taken in various parts of the world. Fishing for whale sharks is banned in the Maldives. The number of divers and hours that divers and boats can approach these animals is restricted in Ningaloo Reef Marine Park to minimize disturbance. White shark is now protected in South Africa, Mamibia, Australia, USA, Maldives and Malta. In addition to declaring full protection for this species, Australia has developed species recovery plans for the white shark and grey nurse shark. Several additional steps have been taken to reduce the accidental kill, injury or disturbance of these animals. Ten grey nurse shark sanctuaries were recently declared in New South Wales waters and there is a total ban on the use of shark fishing gear and the use of mammal blood or oils for attracting sharks in all Victorian waters. There are legislative requirements to report all interactions with white sharks and codes of practice are being developed for eco-tourist activities.

13.7 PRODUCT CERTIFICATION AND ECOLABELLING

Product certification and ecolabelling can be applied in support of fisheries management. Product certification is a measure mandated by governments to ensure that only legally harvested and reported fish landings can be traded and sold on domestic and international markets. Product certification is an extension to normal fisheries management activities. Where there are problems regulating access, such as on the high seas, product certification schemes provide a means of reducing illegal, unreported and unregulated fishing. Ecolabelling programs can create market-based incentives for better management of fisheries by creating consumer demand for seafood products from well-managed stocks by tapping the growing public demand for environmentally preferable products. Criteria used for the accreditation process are a compromise between the demands of consumers and the capabilities and willingness of the producers to meet those demands (Wessells et al., 2001).

13.8 LITERATURE CITED

Allison, G.W., Lubchenco, J. & Carr, M.H. 1998. Marine reserves are necessary but not sufficient for marine conservation. Ecological Applications, 8 (Suppl.): S79–S92.

Anon. 1988. Proceedings of the 17th session of the General Assembly of IUCN and the 17th technical meeting. 1–10 February 1988. San Jose, Costa Rica. World Conservation Union (IUCN): Gland, Switzerland.

Anon. 1994. IUCN red list categories. Prepared by the IUCN Species Survival Commission as approved by the 40th meeting of the IUCN Council, Gland, Switzerland. 21 pp. 30 November 1994. IUCN The World Conservation Union: Gland, Switzerland.

Anon. 2002. The Australian National Plan of Action for the Conservation and Management of Sharks. Public consultation draft. July 2002. Department of Agriculture, Fisheries and Forestry Australia: Canberra, ACT, Australia. 61 pp.

Anon. In press. Status report for the chondrichthyan fishes. IUCN Shark Specialist Group. London.

Au, D.W. & Smith, S.E. 1997. A demographic method with population density compensation for estimating productivity and yield per recruit. Canadian Journal of Fisheries and Aquatic Sciences, 54: 415–420.

Bjordal, Å. 2002. The use of technical measures in responsible fisheries: regulation of fishing gear. In K.L. Cochrane (ed.). A fishery manager's guidebook, management measures and their application, pp. 21–47. FAO Fisheries Technical Paper No. 424. Rome.

Bonfil, R. 1994. Overview of world elasmobranch fisheries. FAO Fisheries Technical Paper No. 341. Rome.

Bonfil, R. 1999. Marine protected areas as a shark fisheries management tool. In Proceedings of the 5th Indo-Pacific Fish Conference. 3–8 November 1997. Nouméa, pp. 217–230. Sociéte Française d”Ichtyologie and Institut de Recherche pour le Développement. Paris.

Botsford, L.W., Catilla, J.C. & Peterson, C.H. 1997. The management of fisheries and marine ecosystems. Science, 277: 509–515.

Branstetter, S. 1999. The management of the United States Atlantic Shark Fishery. In R. Shotton (ed.). Case studies of the management of elasmobranch fisheries, pp. 109–148. FAO Fisheries Technical Paper No. 378/1. Rome.

Camhi, M., Fowler, S., Musick, J., Bräutigam, A. & Fordham, S. 1998. Sharks and their relatives - ecology and conservation. IUCN Species Survival Commission Shark Specialist Group Occasional Paper No. 20. Information Press: Oxford, UK. 39 pp.

Charles, A.T. 2002. Use rights and responsible fisheries: limiting access and harvesting through rights-based management. In K.L. Cochrane (ed.). A fishery manager's guidebook, management measures and their application, pp. 131–157. FAO Fisheries Technical Paper No. 424. Rome.

Compagno, L.J.V. 1984. FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Part 2. Carcharhiniformes. FAO Fisheries Synopsis No. 125: 251–655.

Compagno, L.J.V. & Cook, S.F. 1995. Freshwater elasmobranchs: a questionable future. Shark News, 3: 4–6.

Dowd, W.W. 2003. Metabolic rates and bioenergetics of juvenile sandbar sharks (Carcharhinus plumbeus). M.S. thesis. College of William and Mary, School of Marine Science, Virginia Institute of Marine Science, 152 pp.

Dulvy, N.K., Sadovy, Y. & Reynolds, J.D. 2003. Extinction vulnerability in marine populations. Fish and Fisheries, 4: 25–64.

FAO. 1995. Code of Conduct for Responsible Fisheries. FAO. Rome, 41 pp.

FAO. 2000. Fisheries management 1. Conservation and management of sharks. FAO Technical Guidelines for Responsible Fisheries, Vol. 4(Suppl.1). FAO. Rome, 37 pp.

Forrester, C.R., Ketchen, K.S. & Wong, C.C. 1972. Mercury content of spiny dogfish (Squalus acanthias) in the strait of Georgia, British Columbia. Journal of Research Board of Canada, 29: 1487–1490.

Francis, M.P. 1998. New Zealand shark fisheries: development, size and management. Marine and Freshwater Research, 49: 579–591.

Graham, K.J., Andrew, N.L. & Hodgson, K.E. 2001. Changes in relative abundance of sharks and rays on Australian South East Fishery trawl grounds after twenty years of fishing. Marine and Freshwater Research, 52: 549–561.

Heron, A.C. 1972. Population ecology of a colonizing species: the pelagic tunicate Thalia democratica II. population growth rate. Oecologia, 10: 294–312.

Hilton-Taylor, C. 2000. 2000 IUCN Red List of Threatened Species. The IUCN Species Survival Commission: Gland, Switzerland. 61 pp.

Hoenig, J.M. 1983. Empirical use of longevity data to estimate mortality rates. Fishery Bulletin, 82: 898–903.

Hudson, E. & Mace, G. (eds). 1996. Marine fish and the IUCN red list of threatened animals. Report of the workshop held in collaboration with WWF and IUCN at the Zoological Society of London from April 29th–May 1st, 1996. Zoological Society of London: London, 26 pp.

King, M. 1995. Fisheries biology, assessment and management. Blackwell Science: Carlton, Victoria, Australia, 341 pp.

Kirkwood, G.P. & Walker, T.I. 1986. Gill net mesh selectivities for gummy shark, Mustelus antarcticus Günther, taken in south-eastern Australian waters. Australian Journal of Marine and Freshwater Research, 37: 689–697.

Last, P.R. & Stevens, J.D. 1994. Sharks and rays of Australia. CSIRO Australia: Melbourne. 513 pp.

Lauck, T., Clark, C.W., Mangel, M. & Munro, G.R. 1998. Implementing the precautionary principle in fisheries management through marine reserves. Ecological Applications, 8(Suppl.): S72–S78.

Lotka, A.J. 1922. The stability of the normal age distribution. Proceedings of the National Academy of Science of USA, 8: 339–345.

Myers, R.A. & Worm, B. 2003. Rapid worldwide depletion of predatory fish communities. Nature, 423: 280–283.

Pawson, M. & Vince, M. 1999. Management of shark fisheries in the northeast Atlantic. In R. Shotton (ed.). Case studies of the management of elasmobranch fisheries, pp. 1–46. FAO Fisheries Technical Paper No. 378/1. Rome.

Payne, J. & Andau, P. 2002. Kinabatangan River Conservation Area. In S.L. Fowler, T.M. Reid & F.A. Dipper (eds). Elasmobranch Biodiversity, Conservation and Management. Proceedings of the International Seminar and Workshop. Sabah, East Malaysia. July 1997, pp. 243–244. Occasional Paper of the IUCN Species Survival Commission No 25. IUCN The World Conservation Union: Gland, Switzerland.

Pinkerton, E. 2002. Partnerships in management. In K.L. Cochrane (ed.). A fishery manager's guidebook, management measures and their application, pp. 159–173. FAO Fisheries Technical Paper No. 424. Rome.

Plummer, A., Morris, E., Blake, S. & Ball, D. 2003. Natural Values Study Marine National Parks and Sanctuaries. Report to Parks Victoria. Marine and Freshwater Resources Institute. Queenscliff, Victoria, Australia. 285 pp.

Pope, J. 2002. Input and output controls: the practice of fishing effort and catch management in responsible fisheries. In K.L. Cochrane (ed.). A fishery manager's guidebook, management measures and their application, pp. 75–93. FAO Fisheries Technical Paper No. 424. Rome.

Punt, A.E. & Walker, T.I. 1998. Stock assessment and risk analysis for the school shark (Galeorhinus galeus) off southern Australia. Marine and Freshwater Research, 49:719–731.

Punt, A.E., Pribac, F., Walker, T.I., Taylor, B.L. & Prince, J.D. 2000. Stock assessment of school shark Galeorhinus galeus based on a spatially-explicit population dynamics model. Marine and Freshwater Research, 51: 205–220.

Sant, G. & Hayes, E. 1996. The Oceania region's harvest, trade and management of sharks and other cartilaginous fish: an overview. In The World Trade in Sharks: a Compodium of TRAFFIC's Regional Studies, Vol. 2., pp. 639–806. TRAFFIC International, Cambridge.

Schaefer, M.B. 1957. A study of the dynamics of the fishery for yellowfin tuna in the eastern tropical Pacific Ocean. Inter-American Tropical Tuna Commission Bulletin, 2:245–285.

Schnute, J. 1985. A general theory for analysis of catch and effort data. Canadian Journal of Fisheries and Aquatic Sciences, 42: 414–429.

Simpfendorfer, C. 1999. Management of shark fisheries in Western Australia. In R. Shotton (ed.). Case studies of the management of elasmobranch fisheries, pp. 425–455. FAO Fisheries Technical Paper No. 378/1. Rome.

Smith, S.E., Au, D.W. & Show, C. 1998. Intrinsic rebound potentials of 26 species of Pacific sharks. Marine and Freshwater Research, 49.

Stevens, J. 2002. The role of protected areas in elasmobranch fisheries management and conservation. In S.L. Fowler, T.M. Reid & F.A. Dipper (eds). Elasmobranch Biodiversity, Conservation and Management. Proceedings of the International Seminar and Workshop. Sabah, East Malaysia. July 1997, pp. 241–242. Occasional Paper of the IUCN Species Survival Commission No 25. IUCN The World Conservation Union: Gland, Switzerland.

Stobutzki, I.C., Miller, M.J. & Brewer, D.T. 2001. Sustainability of fishery bycatch: a process for assessing highly diverse and numerous bycatch. Environmental Conservation, 28: 167–181.

Stobutzki, I.C., Miller, M.J., Heales, D.S. & Brewer, D.T. 2002. Sustainability of elasmobranches caught as bycatch in a tropical prawn (shrimp) trawl fishery. Fishery Bulletin, 100: 800–821.

Thompson, G.G. 1992. Management advice from a simple dynamic pool model. US National Marine Fisheries Service Fishery Bulletin, 90: 552–560.

Tricas, T.C., Deacon, K., Last, P., Mccosker, J.E., Walker, T.I. & Taylor, L. 1997. Sharks and Rays. L. Taylor (ed.). Nature Company, Time Life, Reader's Digest and Australian Geographic. San Francisco, USA and Surrey Hills, NSW, Australia. 288 pp.

Walker, T.I. 1976. Effects of species, sex, length and locality on the mercury content of school shark Galeorhinus australis (Macleay) and gummy shark Mustelus antarcticus Guenther from southeastern Australian waters. Australian Journal of Marine and Freshwater Research, 27: 603–616.

Walker, T.I. 1980. Management of mercury content of marketed fish, an alternative to existing statutory limits. Ocean Management, 6: 35–60.

Walker, T.I. 1994. Fishery model of gummy shark, Mustelus antarcticus, for Bass Strait. In I.Bishop (ed.). Resource Technology ”94 New Opportunities Best Practice 26–30 September 1994, pp. 422–438. University of Melbourne, Melbourne. The Centre for Geographic Information Systems & Modelling, The University of Melbourne: Melbourne.

Walker, T.I. 1998. Can shark resources be harvested sustainably? A question revisited with a review of shark fisheries. Marine and Freshwater Research, 49: 553–572.

Walker, T.I. 1999. Southern Australian shark fishery management. In R. Shotton (ed.). Case studies of the management of elasmobranch fisheries, pp. 480–514. FAO Fisheries Technical Paper No. 378/2. Rome.

Walters, C.J. 2000. Impacts of dispersal, ecological interactions and fishing effort dynamics on efficacy of marine protected areas: How large should protected areas be? Bulletin of Marine Science, 66: 745–757.

Walters, C.J. & Bonfil, R. 1999. Multispecies spatial assessment models for the British Columbia groundfish trawl fishery. Canadian Journal of Fisheries and Aquatic Sciences, 56: 601–628.

Walters, C.J., Pauly, D. & Chistensen, V. 1999. Ecospace: prediction of mesoscale spatial patterns in trophic relationships of exploited ecosystems, with emphasis on impacts of marine protected areas. Ecosystems, 2: 539–554.

Wessells, C.R., Cochrane, K., Deere, C., Wallis, P. & Willman, R. 2001. Product certification and ecolabelling for fisheries sustainability. FAO Fisheries Technical Paper No. 422, Rome, FAO, 83 pp.

Williams, H. & Schaap, A.H. 1992. Preliminary results of a study into the incidental mortality of sharks in gill-nets in two Tasmanian shark nursery areas. Australian Journal of Marine and Freshwater Research, 43: 237–250.

Xiao, Y. & Walker, T.I. 2000. Demographic analysis of gummy shark and school shark harvested off southern Australia by applying a generalized Lotka equation and its dual equation. Canadian Journal of Fisheries and Aquatic Sciences, 57: 214–222.


Previous Page Top of Page Next Page