6.1 Resource constraints
6.2 Options to regulate fishing
6.3 Bycatch reduction
6.4 Encouragement of full utilization
6.5 Species conservation
6.6 Biodiversity and ecological considerations
The capacity to manage shark fisheries and conserve species depends on available human and financial resources as well as on the existence of competent institutions. Fisheries management requires an investment of time and resources to collect the needed information, to develop and agree on a management regime, to enforce regulations, and to monitor the fishery. An economically sound fishery should make acceptable returns on investments after the costs of management are accounted for. In subsistence fisheries, management institutions and Shark Plans need to rely more on traditional power structures and culture than on formal management plans.
The management of fisheries to achieve specific goals and objectives requires the development and application of a set of rules that govern the behaviour of fishers permitted to enter a fishery and the gear they use. Rules also govern the behaviour of those not permitted in the fishery, and those without rights of access to certain parts of the fishery. Fisheries practices should be adopted that avoid conflict among fisheries resources users and between these fisheries users and non-fisheries users of resources.
Shark and other chondrichthyan species generally have relatively low productivity and therefore require careful management and monitoring if they are to be utilized sustainably. Hence, in multispecies fisheries where the main target species are bony fishes, sharks landed as non-target species or caught as 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 very wide geographic distributions, others have very restricted ranges falling within the full range of a fishery or the range of other anthropogenic influences (see Appendix 2). Some species have critical habitats such a nursery, parturition and mating areas and migration lanes, which might need special protection.
6.2.1 Control of catch or fishing effort
6.2.2 Control of fishing gear
Fishery managers should ensure that no vessel is allowed to capture sharks or take sharks as bycatch unless authorised in a manner consistent with international law for the high seas or in conformity with national legislation within areas of national jurisdiction.
Fishery managers should ensure that where excess fishing capacity for the capture of sharks exists, mechanisms should be established to reduce capacity to levels commensurate with the sustainable use of shark fishery resources.
Fishery managers should ensure that critical habitats are protected and, where affected by fishing or other human activities, are restored.
Fishery mangers should take appropriate measures to give special attention to protect new-born and young juveniles and breeding adults, particularly for species, which have nursery, pupping and mating grounds. Where appropriate, such measures may include technical measures related to size of shark, use of environmentally safe fishing gear, selectivity of fishing gear, closed seasons and closed areas.
Fishery managers should ensure that existing fishing methods and practices, which are not consistent with responsible shark fishing, are phased out and replaced with more acceptable alternatives. Regulation of fishing gear can be used for control of fishing mortality.
Fishing gear and biological characteristics affect a species’ catchability. Pelagic and semipelagic species that actively swim in the water column are more likely to encounter a gillnet or baited hook and therefore have a higher catchability than sluggish species such as the angel shark, saw shark, certain dogfishes, and batoids that can rest on the seabed. These bottom-dwelling species, on the other hand, are more vulnerable than the more powerful swimming species to demersal trawling.
The fishing gear and biological characteristics can contribute to various kinds of mortality referred to as ‘unaccounted fishing mortality’ or as ‘collateral mortality’. 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 well developed spiracles to aid gill ventilation are better able to ventilate their gills after capture by gillnets and can struggle vigorously to either escape or become more tightly enmeshed in the gear. 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 contributes 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 contributes to ‘unaccounted fishing mortality’. Also, lost gillnets contribute to ‘unaccounted fishing mortality’ through ‘ghost fishing mortality’ until they are rolled into a ball by tidal flow.
Fishing gear selectivity gives rise to a range of complexities that relate to the dynamics of harvested shark species. Selectivity by trawl nets for size of shark is not well understood, and hook-size selectivity for size of shark has been shown to be weak. In gillnets, however, sharks of different sizes are not equally vulnerable to capture. Small sharks 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 their heads cannot so readily penetrate the meshes of the nets. 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 saw sharks and sawfishes, and the dorsal spines of dogfishes, horn sharks and chimaeras. For some species careful regulation of mesh-size can be used to ensure the sharks are large enough to avoid growth overfishing and small enough to facilitate escapement of large breeding animals.
Fishery managers should investigate options for fitting ‘bycatch reduction devices’ in trawl nets to allow escapement of sharks, skates, rays and chimaeras, and regulating construction of the fishing gear and fishing time for gillnets and hooks.
The type of fishing gear used and the species of shark taken as bycatch determines which techniques and equipment are appropriate for minimising bycatch. For trawl nets, there is evidence that catches of sharks have been reduced when fitted with ‘turtle exclusion devices’, suggesting there could 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. Most species of shark remain alive on hooks for extended periods and can be released alive, but 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.
Fishery managers should take appropriate measures to minimize waste of shark, discard of dead sharks, shark catch by lost or abandoned gear, shark catch of non-target species, and negative impacts on associated or dependent shark species, in particular, endangered shark species. Where appropriate, such measures may include technical measures related to size of shark, quantity of fishing gear, mesh-size of fishing gear, discard of sharks, closed seasons and closed areas.
Naturally rare species and species with poor conservation status may require special protection or management through such measures as a prohibition on catch, injury and interference. Where naturally rare species and species with poor conservation status are inevitably killed, injured or interfered with accidentally, consideration should be given to establishing sanctuaries through fishing exclusion zones.
It is not possible to operate a fishery without affecting the original equilibrium of stocks. Fisheries management should promote the maintenance of the quality, diversity and availability of shark fishery resources in sufficient quantities for present and future generations in the context of food security, poverty alleviation and sustainable development. Management measures should not only ensure the conservation of target species but also of species belonging to the same ecosystem or associated with or dependent on the target species.
Fisheries management is required by the 1982 UN Convention on Law of the Sea and by the Code of Conduct for Responsible Fisheries to restore depleted populations to levels above those at which maximum productivity occurs (e.g. to biomass levels higher than the level corresponding to the Maximum Sustainable Yield). This reflects current thinking that providing a margin for safety that takes into account normal variability and uncertainty requires using Maximum Sustainable Yield for fisheries management, rather than as a target.
