Marine and Freshwater Resources Institute
PO Box 114, Queenscliff, Victoria 3225, Australia
1.1 Species composition of fishery
The Southern Australian Shark Fishery is based on several species of temperate-water sharks inhabiting the continental shelf and slope of southern Australia. The fishery covers all species of demersal shark taken commercially by demersal gillnet and demersal hook fishing methods, but operators in the fishery principally target gummy shark (Mustelus antarcticus) and school shark (Galeorhinus galeus). Over the period 1970–97, these two species provided 88% of the shark catch from the fishery, i.e. 47% gummy shark and 41% school shark. The remaining 12% comprised saw shark (Pristiophorus nudipinnis and P. cirratus) (7%), elephant fish (Callorhynchus milii) (2%), and several other species of shark (3%) (Walker et al. 1998a).
Whiskery shark (Furgaleus macki) and dusky shark (Carcharhinus obscurus), which are important in the Western Australian fishery, are taken in small quantities of South Australia and other less important species taken in the fishery in clude broadnose sevengill shark (Notorhynchus cepedianus), blue shark (Prionace glauca), bronze whaler (Carcharhinus brachyurus), mako shark (Isurus oxyrhinchus) and angel shark (Squatina australis).
In recent years several fishers have begun using gillnets on the continental slope to target southern dogfish (Centrophorus uyato) and greeneye spurdog (Squalus mitsukurii), and to a lesser extent endeavour dogfish (Centrophorus moluccensis) and Harrison's dogfish (Centrophorus harrisoni) for liver oil. Along with other species of dogfish, these four species are taken as part of the bycatch in the Southeast Fishery demersal trawl and drop-line fisheries on the continental slope. Total production of dogfish is several hundred tonnes a year but precise estimates are not available because catches of the species are often recorded as ‘dogfish’ or ‘other shark’ or ‘other species’ on logbook returns from the South East Fishery.
1.2 Distribution of fishery
The Southern Shark Fishery (SSF) falls within the Exclusive Economic Zone of Australia. While the New South Wales—Victoria border and South Australia—Western Australia border are the management boundaries of the fishery off Victoria, Tasmania and South Australia, the range of the species includes both Western Australia and New South Wales. In both Commonwealth and State waters off New South Wales, gillnetting is currently banned. In waters off Western Australia, shark fishing is controlled through a Joint Authority between the Commonwealth and Western Australian Governments established under a separate Offshore Constitutional Settlement agreement.
Gummy shark are endemic to southern Australia from at least Port Stephens (New South Wales), around Tasmania, and to Geraldton (Western Australia). They are demersal and are taken mainly on the continental shelf from the shore to about 80m depth, but sometimes on the upper slope down to 350m. Very similar (possibly the same) species of gummy shark occur on the east and west coasts of Australia between latitudes of about 17° and 30°S in depths between 120 and 400m (Last and Stevens 1994).
School shark are distributed around southern Australia mainly on the continental shelf and upper slope where they have been recorded from Moreton Bay (southern Queensland) to Perth (Western Australia), including Tasmania. They have been taken from the shore to 550m depth mainly near the bottom, but are known to occur in the pelagic zone and well offshore. Tagging studies have demonstrated trans-Tasman migrations between southern Australia and New Zealand (Coutin et al. 1992; McGregor 1994; Walker et al. 1997). This species is likely to form a single stock in southern Australia. School sharks also occur on the west coast of North America, the east coast of South America, around southern Africa and in the eastern North Atlantic (Last and Stevens 1994).
1.3 Associated species either as bycatch or discards
Bycatch from the fishery is low. Small catches of silver trevally (Pseudocaranx dentex), longsnout boarfish (Pentaceropsis recurvirostris), nannygai (Centroberyx affinis), blue warehou ( Seriolella brama), spotted warehou (Seriolella punctata) and John Dory (Zeus faber) are marketed. Draughtshark (Cephaloscyllium laticeps) and Port Jackson shark (Heterodontus portusjacksoni) are discarded live.
It is likely that school shark form a single stock whereas gummy shark form regional substocks across southern Australia. Genetic studies, tag releases (1942–56, 1973–76 and 1990–96) and their subsequent recapture, investigations of mercury contamination of axial muscle tissues in 1972, and biological sampling (1973–76 and 1986–87) all provide evidence that mixing rates of gummy shark are lower than mixing rates of school shark.
Genetic variability is much higher in gummy shark than in school shark (Ward and Gardner 1997). Tag release-recapture data indicate that the mean distances travelled by gummy sharks are short compared to distances travelled by other species of shark such as school shark (Olsen 1953, 1954, 1984; Walker 1983; Walker et al. 1997). Mercury concentrations in gummy shark varied significantly between separate localities whereas no variation between separate localities was detected for school shark (Walker 1976). Similarly, ratios of various elements in the cartilage of jaws from gummy sharks caught off Western Australia were found to vary between separate localities (Western Australian Marine Research Laboratories, unpublished data).
Scientific sampling indicates that juvenile and pregnant gummy sharks are found in most areas across southern Australia at all times of the year. This is consistent with the occurrence of discrete substocks, although there is currently no firm basis for delineating them. The single stock hypothesis for school shark is supported by evidence from scientific sampling that pupping areas of school shark tend to be in the eastern region of southern Australia and that pregnant school sharks tend to aggregate in the Great Australia Bight before August along with documented long-distance tag movements.
Attempts at modelling the fishery in the past have either assumed a single stock of gummy shark and a single stock of school shark for the entire fishery or assumed several substocks of gummy shark and several substocks of school shark. The substocks were defined arbitrarily on convenient geographical areas and modelled as independent stocks.
2. NATURE OF THE FISHERY
2.1 Present status
Today most of the catch is taken by gillnet. Although most of the catch was taken by longline prior to the 1970s, in 1996 only 6% was taken by this method. In addition, bycatches of shark are taken in the demersal trawl, drop-line, offshore tuna surface longline and inshore scale fish fisheries. Recreational fishers take shark, particularly juveniles, in bays and estuaries and to a lesser extent, off ocean beaches.
At present a total of 125 Commonwealth Fishing Permits to use gillnets and 35 Commonwealth Fishing Permits to use hooks have been issued by the Australian Fisheries Management Authority (AFMA) to take demersal sharks in Commonwealth waters. These permits are issued one per vessel with the exception that four vessels each have a gillnet permit and a hook permit; these four pairs of permits cannot be split. Most of these vessels have one or more State licences to operate in State proclaimed water, although the use of shark gillnets and shark longlines are prohibited in Victorian State proclaimed waters, with the exception of limited used of shark longlines in Western Port Bay and Corner Inlet. In addition, 455 vessels took shark with shark gillnets or shark longlines in State proclaimed waters of Victoria (excluding bays and inlets), Tasmania, and South Australia during 1997 and several hundred other vessels each landed small quantities of shark from Commonwealth and State proclaimed waters off Western Australia and New South Wales.
2.2 The harvest process
2.2.1 Longline fishing
Longlines were the original method used to catch shark but were largely replaced by gillnets during the second half of the 1960s and early 1970s. The longline consists of a sinking main-line constructed of 6–8mm diameter synthetic rope (traditionally manilla or sisal rope) with snoods about one metre long attached at intervals of 6–10m. Each snood carries a 10/O short-shank (with monol wire trace) or 11/O long-shank Mustad hook (without trace) at one end and is attached to the main-line at the other either permanently or by means of a “snood clip” (introduced to into the fishery in the late 1960s).
This gear is divided into a number of “sets” where each set has up to 300 hooks. The hooks together with the main-line and an anchor weight at each end are placed on the seabed. Until adoption in Commonwealth waters of a 2000-hook limit recently, more than 2000 hooks were commonly used during a single fishing operation; however, the average was less than half this. Common baits used include eels, snoek and squid. Fresh bait is more effective than frozen bait.
A buoy and dahn pole with flag are attached by way of buoy-line to the main-line at each end for retrieval of the gear. The main-line is hauled from one end over a roller mounted on the gunnels by a line hauler, usually situated in the mid-section of the vessel, into a box.
Longline fishing has several advantages over gillnet fishing:
longlines can be readily set in deep water on the continental slope where there is the highest risk of losing gillnets,
longlines can be set in strong tidal currents where gillnets cannot be used effectively,
the sharks are usually captured alive and therefore less likely to be damaged as a result of being eaten by “sea-lice” (mainly isopods and copepods), leatherjackets or other sharks, and
longline fishing gear and appropriate hauling equipment are much cheaper to purchase and maintain than gillnet fishing gear.
An important development in longline fisheries in other parts of the world, which has spread to Australia, is the use of machines which attach baits to the hooks and facilitate rapid automatic attachment of the snoods to the main-line when setting the gear and facilitate removal of the snoods when hauling the gear. These labour saving devices are currently prohibited in the Southern Australian Shark Fishery because they would inevitably increase the number of hooks set and the period a vessel can operate each day.
2.2.2 Gillnet fishing
Gillnet fishing does not need bait and, apart from a few areas of strong tidal flow, is much more efficient than longlines for catching gummy shark and equally effective for catching school shark. The method also has the advantage in that gillnets can be designed to catch a particular size range of sharks.
The monofilament gillnets introduced in to the fishery at Lakes Entrance, Victoria, during 1964 were of 51/2 inch (140mm) and 53/4-inch (146mm) mesh-size. Until a ban on the sale of large school shark in Victoria because of their mercury content during 1972, the trend had been to increase mesh size to a maximum of 8-inch (203mm) mesh-size with most of the fleet adopting the 7-inch (178mm) mesh. However, following the ban, there was a rapid trend to smaller sizes, the most favoured being the 6-inch (152mm) mesh-size. In several cases 5-inch (127mm) mesh-size was adopted in Bass Strait but legislation adopted by Victoria, Tasmania, South Australia and the Commonwealth restricting the minimum size to 150mm (approximately 6 inches) contained this trend.
The gillnet consists of a stationary net, anchored and buoyed at each end. The net is normally monofilament polyamide webbing slung with a hanging ratio of between 0.5 and 0.7. The head-line is made of 8–12mm diameter polypropylene rope with floats of 80–120g upthrust attached at intervals of 5–10m. The lead-line usually consists 6–9mm polyethylene with several 60–90g lead weights per float. The nets are mainly 20, but historically 10–20, meshes deep and the breaking strain of the net fibre is between 300 and 400 Newton. Gillnets up to 40 meshes deep for deployment in both the shark fishery and the deep—sea gillnet fishery for scale fish are being used from a few vessels operating from eastern Victoria.
The nets are normally made from 1000 yard (914m) bales of webbing and depending on hanging coefficient this can be made in to a net between 450 and 650m long with an average of about 550m. Several of these nets are joined and set together as a “fleet” with a buoy and dahn pole attached by a buoy-line and with an anchor at each end.
Each “fleet” of nets is set by the vessel moving slowly forward and allowing the nets to run off a winch spool and over the stern of the vessel; first, a buoy and dahn pole attached to the end of a buoy-line, next, one end of the nets with an anchor weight attached, then, the rest of the nets with anchor weights attached at various distances along the nets, and, finally, another buoy-line with buoy and dahn pole. Depending on the total length of nets one or more fleets are set during a single operation. The nets rest vertically with the lead-line on the seabed.
The gear is retrieved by hauling it from one end over a roller, which is usually mounted near the bow, and onto a hydraulically or, in a few cases, mechanically powered winch spool. Until early 1988 up to a total length of 8000m of nets were used during a single fishing operation, but this was limited to 6000m during 1988–90 and since then has been further limited to 4200m.
During 1971 the use of a flashing light mounted on each dahn pole became widespread within the fishery and enabled the nets to be found and hauled at night. This had the effect of extending the effective fishing time per 24h period and thus the total fishing effort expended on the stocks. However, the introduction of the lights also had the benefit of reducing the practice by some fishers of leaving the nets unattended in the water for long periods and overnight, a practice causing wastage of shark through spoilage and damage from “sea-lice” and other fish.
2.3 Evolution of catch
Although small quantities of shark have been taken since European settlement for liver-oil, fins, bait, fertilizer and leather, Olsen (1959) dates the start of the shark fishery of southern Australia as 1927 when the Melbourne Fish Market recorded a throughput of 4t, carcass weight. The fishery in oceanic waters was initiated by rock lobster fishers in Victoria who caught sharks with hooks for rock lobster bait. Because of transportation and storage difficulties the fishery was restricted to central and eastern Bass Strait waters, closest to the Melbourne Fish Market. By the mid-1930s annual catches were around 400–500t.
When the Second World War created a national demand for greater food production and an overseas, as well as a local demand for vitamin A from shark liver oil, the fishery expanded rapidly to include, with the exception of the west coast, most regions around Tasmania and south-eastern region of South Australia. The demand for liver oil after the war continued and between 1944 and 1949, when liver-oil prices peaked, the fleet in Victoria alone grew from 35 to 62 (excluding vessels working from Lakes Entrance) and the fishery rapidly spread to central and western South Australia and the overall catch reached approximately 2000t.
Initially, fishers used several hundred baited hooks attached to bottom-set longlines to target large mature school sharks over the summer months as they entered shallow waters to pup. Large mature gummy sharks were often taken as a non-targeted catch. As the abundance of adult school shark in shallow water declined shark fishers targeted sub-adult sharks further offshore out to the continental slope. For vessels working out of Stanley, northwest Tasmania, during the 1940s, Olsen (1959) recorded catch rates for school shark declining by 70% and the distances of trips increasing from 3 to 24 miles. By 1943 vessels working off the Victorian coast were fishing 40–60 miles south and seaward of their home ports. Between 1944 and 1956 the catch rates of Victorian vessels fell by more than half. Without effort control the catch of school shark pups in Port Phillip Bay declined by around 80% between 1942 and 1955.
The price of shark liver oil collapsed in 1949 and the fishery for sub-adult school shark in Victoria became uneconomic because their livers have a lower oil content and attracted lower prices. Many Victorian fishers switched to other fisheries, moved west into South Australia (around Robe and Port Lincoln), or south into Tasmania where large mature school sharks could be targeted. Through the 1950s catches from Victoria and Tasmania fell by more than 50% while South Australian catches doubled. Overall catches remained around the 1940s level. Olsen noted the same pattern of development in the new fishing grounds of South Australia; initially large adult sharks were targeted inshore during spring but the fishery moved to targeting smaller sub-adults on the shelf as adult stocks declined.
There was no further growth in the fishery until the early 1960s as the demand for shark meat grew in Victoria. During 1964, the Victorian fishers introduced gillnets into the fishery and by the early 1970s, most of the catch was taken by this method. Production rose rapidly during the 1960s and peaked in 1969 at 3756t untrimmed carcass weight consisting of mainly school shark. During the 1970s, production declined initially in response to declining stocks of school shark, but catches fell sharply in 1972 when the 1972–85 ban on the sale of large school shark was first adopted because of their mercury content. For the rest of the 1970s gummy shark replaced school shark as the predominant species then during 1980–87 school shark was the predominant species, but since 1988 the school shark catch has fallen rapidly while the gummy shark catch has remained high. After reaching a second peak in 1986, the total catch of gummy shark and school shark combined has subsequently declined, partly in response to restrictions on the use of gillnets and partly in response to a decline in the abundance of school shark (Figure 1).
The transition from targeting school shark to targeting gummy shark that occurred in Bass Strait during the early 1970s occurred later in South Australia around St Vincent Gulf, Kangaroo Island and the Coorong during the late 1970s and early 1980s when the annual gummy shark landings rose from about 100 to 400t. In southern and western Tasmania and west of Port Lincoln the fishery has remained a fishery targeting school shark although there is some evidence that the fishery around Port Lincoln is now beginning the same transition.
In Western Australia, longline and gillnet fishing for shark species developed rapidly during the 1980s. Gummy shark provide an important component of the shark catch taken off the south coast of Western Australia. Annual catches during 1991–97 were 324, 329, 186, 168, 158, 173 and 205t, untrimmed carcass weight. Fishing in deeper water recently led to increased targeting of school shark on the south coast of Western Australia but this trend appears to have reversed. Annual catches during 1991–97 were 82, 105, 95, 41, 55, 35 and 37t. Other important species in the catch include whiskery shark and dusky shark.
Catch of gummy shark and school shark during 1930–97
Off New South Wales the narrowness of the Continental shelf limits the area of habitat suitable for gummy shark and school shark and so those stocks support only a few longline vessels. Monofilament gillnets are banned off New South Wales and most sharks are taken as a bycatch in trawl and inshore scale fisheries. Demersal trawl vessels take mainly dogfish and angel shark and only small quantities of gummy shark and school shark.
During 1970–97, the overall catch comprised 47% gummy shark, 41% school shark, 7% saw shark, 2% elephant fish, and 3% other species. Of this overall catch, landings were 49% for Victoria, 20% for Tasmania and 31% for South Australia (Table 1). Trends in production of the less important species of saw shark, elephant fish and ‘other species’ are given in Figure 2. The increase in ‘other species’ in recent years is mainly a result of increased catches of dogfish. While the total catch over this period remained remarkably constant for Victoria, it varied considerably for South Australia and Tasmania.
|State||Percentage of 1990–97 catch||Percentage of 1997 catch|
Source: Walker et al. (1998a).
2.4 Fleet characteristics, evolution of the fleet and fishing effort
When the fishery began, shark fishing was undertaken from small wooden ‘couta’ boats fitted with sails but these were soon replaced by larger wooden vessels powered by diesel engines as fishers moved further off shore and remained at sea for several days. Since the 1960s there has been a trend to replace the wooden vessels with steel vessels.
Catch of minor species of shark during 1970–97
During the early stages of the fishery the boats were engaged primarily in the rock lobster fishery taking southern rock lobsters (Jasus edwardsii) and shark fishing was done on a part-time basis. Later, as the fishery developed, there was a trend towards specialization, but even today most of the catch is taken by a relatively small number of specialist vessels. A large number of vessels take small quantities of shark, but are primarily engaged in the inshore scale fish and rock lobster fisheries with a few in the commercial scallop (Pecten fumatus) and trawl fisheries.
There were 301 vessels with a Commonwealth Fishing Boat Licence that reported shark on at least one monthly catch and effort fish return during the 3-year period from October 1981 to September 1984. Of these 301 vessels, 175 took the majority of their catch using gillnets and 126 using longlines. In addition, several hundred vessels took small quantities of shark within the State proclaimed waters, some with shark monofilament gillnets or shark longlines, but also as a bycatch with other types of gear in other fisheries (Walker 1989b).
The 301 vessels with Commonwealth Fishing Boat Licences had a mean length of 14.5m and ranged from 5 to 32m with the majority (86%) from 10 to 20m. The vessels remaining at sea for several days possess ‘ice-holds’, ‘refrigerated-holds’ or ‘brine-tanks’ for storing the catch, whereas smaller vessels returning to port each day tend to carry the catch either on the deck without ice, in an ‘ice-hold’ or in a ‘wet-well’.
During the 25-year period 1973–97, 11% of gummy shark, 23% of school shark, and 16% of gummy shark and school shark combined was taken by longline. Of the overall catch of gummy shark and school shark combined, 10% was taken by longline in Tasmania whereas about 3% was taken on longlines by each of Victoria and South Australia. The proportion of gummy shark captured by longline has remained relatively constant during 1973–97, whereas the proportion of school shark has been much more variable and declining. The school shark catch taken by longline was 31% during 1973–81 and 23% during 1982–95; by 1997 it had declined to 8%.
Nominal ‘equivalent gillnet effort’ peaked during 1987 at 120 000km-lifts1. This was determined by weighting up the nominal total gillnet effort of 99 000km-lifts during 1987 from the gillnet catch to the combined gillnet and longline catch. This peak followed an increase from 25 000km-lifts (21% of peak effort) during 1973 and was subsequently followed by a decline to 56 000 km-lifts (47% of peak effort) during 1996. This returned to 66 000 km-lifts during 1997 (Walker et al. 1998a).
School and gummy shark are the most important species in the SSF. At the Melbourne Fish Market, prices varied between A$5.50 and A$8.50/kg during 1994, with an average price of around A$7.00/kg. Larger shark received around a 10%/kg lower price then those in the 4–6 kg range. The other major species of shark caught in the fishery, elephant fish and angel shark averaged under A$2.00/kg while saw shark averaged around A$3.00/kg. This pattern of price was similar through to 1997.
Most of the Victorian landed product is wholesaled as carcasses on the Melbourne Fish Market where it is sold to fish and chip shops, the retail sector and through restaurants as ‘flake.’. Sharks landed in Tasmania, South Australia and Western Australia are often first sold to local processors before marketing in Victoria. Prices for shark are generally higher for product marketed directly on the Melbourne Fish Market than those marketed to local processors in Tasmania, South Australia and Western Australia. This pattern of distribution and pricing has persisted for much of the history of the fishery. Shark meat is often imported from other parts of the world but rarely exported.
2.5.2 Revenue from the fishery
The gross value of the catch from the SSF has been steady at about A$15 million to A$17 million during 1993–97. The value is estimated from catch and mean price per kilogram of shark carcass received by the fishers.
2.6 Economics of the fishery
Effort has been markedly reduced in the SSF in recent years and economic surveys of the fishery during 1992/93, 1993/94 and 1994/95 indicate that there was a strong improvement in the performance of those operators who were most heavily reliant on shark receipts. For specialist shark operators (defined as those earning more than 80% of their total receipts from sales of shark per vessel turned from a loss of nearly A$11 000 during 1993/94 to a profit of over A$31 000 during 1994/95.
A major influence on the financial performance of vessels in the SSF are gear entitlements and income from fishing operations in other fisheries. During 1994/95, for example, the average total cash receipts for operators in the SSF was A$265 000. Of this, A$124 000 was from shark while the rest came from other fisheries. The southern rock lobster fishery provided 36% of the total, the commercial scallop 6%, and other fisheries or non-fishing activities 10%. Average cash receipts from sale of fish varied across the fleet, i.e. receipts were A$202 000 total (A$25 000 from shark) for vessels with 2–5 units under their Commonwealth Shark Gillnet Permits, A$275 000 total (A$123 000 from shark) for vessels with 6 units, A$307 000 total (A$250 000 from shark) for vessels with 10 units, and A$301 000 total (A$78 000 from shark) for vessels with 1000 or 2000 hook units under their Commonwealth Shark Hook Permits. Average vessel profit after wages, vessel running costs, interest and vessel depreciation was A$44 000 (ABARE 1996).
1 A km-lift is one lift of one kilometre of gill netting, e.g. a 4200m gillnet lifted twice gives 8.4km-lifts.
2.7 The fisheries workforce
While average crew numbers varied between the categories of vessel, most vessels carried one or two crew members in addition to the skipper. Smaller vessels had generally fewer crew. About two-thirds of the skippers are owner operators while the rest are employed skippers.
3. MANAGEMENT OBJECTIVES
3.1 The fisheries within the context of national fisheries policies
The Southern Shark Fishery is currently managed under four separate jurisdictions. State fisheries agencies in Victoria, Tasmania and South Australia have jurisdiction over State proclaimed waters (out to 3 nautical miles or more for some enclosed waters) and the Australian Fisheries Management Authority (AFMA) has jurisdiction from this limit to the edge of the Australian Fishing Zone (200nm offshore). Co-ordination of management between the Commonwealth and States is done through the Ministerial Council on Forests, Fisheries and Aquaculture, which includes the membership of the Commonwealth and State Ministers of Government with responsibility for fisheries.
To simplify management arrangements the Commonwealth and State Ministers responsible for fisheries in Victoria, Tasmania and South Australia have agreed to place the majority of the fishery under a single jurisdiction. This can be achieved under the Commonwealth Fisheries Amendment Act 1980, which is part of a parcel of 14 Acts termed the Offshore Constitutional Settlement (OCS) and enacted on 14 February 1983. This makes provision for managing fisheries under joint authorities of the Commonwealth and one or more States, or by the Commonwealth only, or by one State only (Anon 1989). The Fisheries Ministers have agreed that the fishery be managed under Commonwealth law. Resolution of these jurisdictional arrangements will be incorporated into an Offshore Constitutional Settlement agreement and a Memorandum of Understanding between the Commonwealth and States that is close to finalization.
State Internal Waters will continue to be managed by the States. These are waters inside the baselines defining the inner edges of the States' 3-mile limits. The baselines run from point to point, enclosing considerable bodies of water where coastlines are indented or where there are islands or rock outcrops. Substantial areas of internal State proclaimed waters occurring adjacent to the SSF include Spencer Gulf and Gulf of St Vincent in South Australia, and areas of Bass Strait around Tasmanian islands and most of the inshore and estuarine areas around south-eastern Tasmania. The bays and inlets of Victoria all form internal waters but the main ones where school and gummy shark occur are Port Phillip Bay, Western Port and Corner Inlet. The State fisheries agencies and AFMA have agreed to apply complementary management arrangements in the areas under their jurisdictions.
Objectives for fisheries managed by Australia's National Government are outlined in the Australian Government Policy Statement of December 1989 ‘New Directions for Commonwealth Fisheries Management in the 1990s’.
Ensure the conservation of fisheries resources and the environment which sustains those resources
Maximize economic efficiency in the exploitation of those resources
Collect an appropriate charge from fishers exploiting a community resource for private gain.
The Australian Government Policy Statement is cognizant of the global experience that unregulated fisheries tend to be over-exploited and over-exploitation, at the least, means lower returns from the fisheries and, at worst, can lead to elimination of biological species. Management controls that maximize economic efficiency involve a lower level of fishing effort and lower costs than in an uncontrolled situation, and are consistent with the objective of biological sustainability of the resources.Because of the lower costs associated with the reduced effort under controlled management the profits from exploiting fisheries resources are increased. As fisheries resources are the property of the Australian people it is appropriate for a charge to be imposed when individuals gain significant benefits from the exploitation of a public resource.
The guiding principles adopted to achieve the overriding objectives are that management controls should not distort the way economic resources are allocated (economic efficiency), similar people in similar circumstances should receive similar treatment (social equity), management controls should be straight forward and clear-cut (administrative efficiency), and management programmes should contain clear objectives and the controls should be periodically tested against management's aims (management effectiveness).
The Australian Government Policy Statement recognizes fishing is usually constrained by restrictions on catches such as quota, or on inputs, such as number of vessels or net sizes. Each fishery has special characteristics such that in some input controls are appropriate and in others, output controls are appropriate. In some situations, regulations such as restrictions on driftnets are essential to protect the environment. In general, to allow market forces to operate, the preferred management option is the use of individual transferable quotas. Before other management controls are used, fishery manages have to demonstrate that these controls are superior to transferable quotas for a particular fishery.
3.2 Objectives for the management of the fishery
The Southern Shark Fishery is currently managed under a range of stated goals, immediate objectives and long-term objectives.
To ensure that management arrangements in place in the southern Australian shark fishery result in the conservation and sustainable use of the resources in the fishery
To promote the rebuilding of depleted fish stocks and identify and facilitate commercial exploitation of alternative species of demersal sharks
To encourage the efficient exploitation of resources of southern Australian shark fishery
To implement effective and efficient management of the fishery.
3.2.2 Immediate objectives
Develop an environment where industry, managers and scientists work together in a co-perative and open way to address management issues in the best interests of the fishery, its participants and the wider community
Identify stock structure and movement patterns for school and gummy shark
Implement management arrangements which will aim to: (1) stabilize stocks of gummy shark at the 1994 level; (2) ensure that there is an 80% probability that in 2011, the mature biomass of the school shark stocks are above the 1996 level.
3.2.3 Long-term objectives
Maintain each individual stock in the fishery at a level (which may be determined by AFMA from time to time with advice from the Southern Shark Fishery Management Advisory Committee) at or above 40% of the initial biomass
Provide management arrangements that will encourage industry profitability and the best possible return from the resource.
3.3 The objective setting process
The Southern Shark Fishery Management Advisory Committee (SharkMAC) advises the AFMA Board on the management of the fishery. SharkMAC comprises an independent Chairman, five industry members, a State Government member, a research member, a member who represents the conservation interests the public and an AFMA member.
SharkMAC has several subcommittees. The Shark Industry Research Liaison Committee (SIRLC) sets research priorities for the fishery and evaluates applications for funding from various research funds. The Southern Shark Fishery Assessment Group (SharkFAG), which works closely with SIRLC, undertakes and reviews stock assessments and economic assessments of the fishery and recommends further research required to improve assessments and resolve uncertainties. Both SIRLC and SharkFAG are comprised of scientists, shark industry members and the AFMA Manager of SSF. To provide for equitable quota management an Allocation Advisory Panel will be established to provide advice to the AFMA Board on the most appropriate allocation process for the fishery.
The history of multiple jurisdictions over the SSF has complicated and often slowed negotiations and implementation of management changes and industry restructure. Also it has raised costs of managing the fishery and complicated fishery monitoring data sets through different spatial and temporal resolutions and quality of the data.
Consultative processes implemented by AFMA for dialogue between the SSF managers, industry members, economists and scientists involved in shark biology and stock assessment during the last 5 years have proved to be effective. Interaction between AFMA, SharkMAC, SharkFAG and SIRLC has produced stock assessments accepted by scientists, industry and the managers. Management goals and objectives have been set and are reviewed as stock assessments are updated and harvest strategies developed. Industry meets most of the cost of management and monitoring of the fishery and some of the cost of research through industry levy.
4. MANAGEMENT POLICIES AND THE POLICY SETTING PROCESS
4.1 Management policies adopted
4.1.1 Resource access
Apart from the requirement for vessels to be registered as fishing vessels by the Commonwealth and State fisheries agencies and the prohibition on the use of shark fishing gear in some areas, the Southern Shark Fishery was an open access fishery until 1984. Following the first meeting of the Southern Shark Task Force in September 1984, the Commonwealth began endorsing Commonwealth Fishing Boat Licences (subsequently replaced with Commonwealth Fishing Permits) with ‘shark gillnet endorsements’. An endorsement allowed an operator to use a vessel to take shark with gillnets of mesh-size exceeding 150mmin Commonwealth waters.
Later, in April 1988, the use of gillnets in the prescribed area of the SSF was controlled by the Southern Shark Fishery Management Plan established under the Fisheries Act 1952 (now repealed and replaced by the Fisheries Management Act 1991). The objective of this plan was to reduce the fishing mortality of sharks to provide for sustainable catches through reduction of gillnet fishing effort. This reduction of effort was implemented by controlling the number, size and construction of gillnets and the number operators who were permitted to use them.
4.1.2 Gear restrictions
Under the management plan, a unit of gillnet fishing capacity, referred to as a ‘net unit’, was created. Each net unit permitted the use of a standard gillnet defined as a monofilament gillnet with a head-line length of 600m, 20 meshes deep and with a mesh-size no less than 150mm. Mesh-size was defined as the distance between opposite knots of the mesh diamond when pulled apart taut. The depth of a gillnet could be increased to more than 20 meshes provided there was a corresponding decrease in its head-line length and approval to make the alternation was given by the manager of the fishery (i.e. overall area of the gillnet had to be the same).
Net units in the fishery were issued to each operator on the basis of catch history and number of gillnets used during the 5-year qualifying period from September 1979 to September 1984. Based on a vessel's catch history during the qualifying period, each shark gillnet endorsement was classed as either a Category A endorsement or a Category B endorsement. Operators who had a total catch history of 45t or more taken during any 3 of the 5 years of the qualifying period were considered to be engaged full-time in the fishery and given a Category A endorsement and 6 net units. These were referred to as A6 endorsements. The operators who did not qualify for a Category A endorsement were considered to be engaged part-time in the fishery and given a Category B endorsement and either 5, 4, 3 or 2 net units depending on the number of gillnets used during the qualifying period. These were referred to as B5, B4, B3 and B2 endorsements, respectively and most operators with these endorsements were licensed to operate in other fisheries, notably rock lobster and scallop.
A total of 241 endorsements and 1234 net units were issued. An annual levy, payable to the Australian Fisheries Service (predecessor of AFMA), was charged for each unit. These units were non-transferable outside immediate family members. Non-transferability of shark gillnet endorsements, in conjunction with the policy enforced by the Commonwealth and State fisheries agencies of prohibiting the splitting of licence packages, markedly reduced the number endorsements and net units in the fishery.
To reduce the number of full-time vessels engaged in the fishery, the management plan allowed for amalgamation of two A6 endorsements to provide for an A10 endorsement with 10 net units. An amalgamation involved the forfeiture of 2 of the 6 net units attached to the A6 endorsement on one licence and the transfer of the remaining 4 net units to a second licence. The amalgamation process, which ended on 30 May 1990, created 40 separate A10 endorsements and removed 40 vessels and 80 net units from the fishery.
The requirement by all Category A and Category B endorsement holders to pay levies also contributed to a decline in the number of vessels and gillnet units in the fishery as it became less profitable to continue in the fishery at a low level. This levy was based on the number of net units and was collected to meet management costs. There was no difference in the cost per net unit between Category A and Category B endorsements. Any endorsement holder who failed to pay the levy within 60 days of the due date had their endorsement and net units cancelled and could not participate in the gillnet fishery from that time. At present there are 125 vessels with net units in the fishery. Of these, 40 vessels have A10 endorsements, 28 have A6 endorsements and 57 have Category B endorsements.
During February 1991, the former Southern Shark Research Group (subsequently replaced by SharkFAG) advised SharkMAC that, in spite of effort reductions, the shark fishery was in danger of collapse without further reductions. Government and scientific members of SharkMAC recommended an across-the-board net reduction of 50%. The Minister met with industry representatives and on 15 April 1991 the former Australian Fisheries Service implemented interim net reductions of 30% for A10 endorsements, 33% for A6 endorsements, 40% for B5 endorsements and 25% for B4 endorsements. B3 and B2 endorsements were not altered. This reduced the number of net units in the fishery by about one third. Later, on advice from SharkMAC in April 1993, the AFMA Board restored the number of net units and applied a uniform 30% reduction on all shark endorsements by reducing the standard net length for a net unit from 600m to 420m.
On 3 February 1992, the Fisheries Act 1952 was superseded by the Fisheries Management Act 1991 which replaced the Australian Fisheries Service with the Australian Fisheries Management Authority (AFMA) as the Commonwealth's fisheries management agency. Under the new Act Commonwealth Fishing Boat Licences were replaced with a system of Commonwealth Fishing Permits and more permanent Statutory Fishing Rights. In replacing the Fisheries Act 1952, legislation established under this Act, such as the Southern Shark Fishery Management Plan became void. Until a Management Plan under the Fisheries Management Act 1991 is developed, the fishery will be controlled through conditions on Commonwealth Fishing Permits. The conditions on these Permits reflect the Southern Shark Fishery Management Plan under the Fisheries Act 1952. It is anticipated that the Fishing Permits will be replaced by Statutory Fishing Rights when a new Southern Shark Fisheries Management Plan is determined under the Fisheries Management Act 1991.
During 1993, SharkMAC developed entry criteria and management arrangements to apply to the hook sector from 1 January 1994. AFMA advised all holders of Commonwealth Fishing Permits allowing the use of demersal hook fishing methods that they would be required to meet prescribed entry criteria to take school and gummy shark by hook methods after 1 January 1994. By 1 July 1995 31 applicants had been granted Shark Hook Permits to use either 2000 or 1000 hooks depending on catch history. By 6 June 1996 this had increased to 35 Shark Hook Permits.
The Shark Hook Permits are referred to as H2000 and H1000 Permits (Table 2) and the holders of these contribute to the cost of management through the payment of levies. Levies for the hook sector are set relative to levies for the gillnet sector on the basis of the relative catch of gummy shark and school shark combined between the two sectors. An H2000 Permit holder pays double the levy of an H1000 Permit holder and where a Permit holder has both a Shark Gillnet Permit and a Shark Hook Permit levies are paid on both in recognition of the greater access for the fishery.
|State||Number of net permits||Number of hook permits|
Source: AFMA (6 June 1996); Four boats have both net and hook permits.
Applicants unsuccessful in gaining access to the hook sector of the SSF are permitted to continue to use demersal hook fishing methods in Commonwealth waters but are limited to a trip by catch of five carcasses of gummy and school shark combined.
4.1.3 Vessel regulations
Vessel regulations are not applied for management of the fishery, but all vessels must possess a maritime survey certificate.
4.2 Biological regulations
A number of biological regulations proclaimed under Commonwealth law, or State law, or both, are either currently in place or have been adopted and subsequently abandoned. These regulations include legal minimum lengths, a legal maximum length, legal minimum and maximum mesh-sizes of gillnets, closed seasons and closed areas.
Legal minimum lengths were phased in by the States and Commonwealth during 1949 and the early 1950s and remain current. The legal minimum length for school shark was 91cm total length throughout the range of the fishery but for gummy shark was 61cm in Victoria and 77cm in Tasmania and South Australia. Because sharks are landed headed and gutted, during 1975–77 the lengths were revised to partial lengths (fifth gill-slit to base of caudal fin) of 40cm (equivalent to 71cm total length) for school shark and 45cm (equivalent to 75cm total length) for gummy shark.
A legal maximum length on school sharks marketed in Victoria, designed to reduce the average concentration of mercury in the catch, applied during 1972–85. It was 104cm total length but was revised during 1976 to 63cm partial length (equivalent to 112cm total length). The legal maximum length was abandoned in June 1985 following revision of the Australian food standard for mercury in fish from a statutory limit of 0.5mg/kg to a mean of 1.0 mg/kg (i.e. 1.0mg of mercury/kg of shark meat expressed as a wet weight of 80% moisture).
Closed seasons during October or November (the months prior to when school sharks give birth) to protect pregnant female school sharks were adopted during 1953–67. More recently, during 1993 and 1994, seasonal restrictions were imposed to provide some protection to pregnant school sharks migrating to nursery areas. During 1993 the landing of shark was limited to five carcasses during November in the area west of the South Australia-Victoria border and during December in the area east of this border. During 1994, the taking of gummy and school shark and the use of gillnets were prohibited during the period from 8 October to 22 November for the area west of the border and during the period from 11 November to 25 December for the area east of the border, except for a small number of vessels targeting blue warehou (Seriolella brama) off eastern Victoria with gillnets of large mesh-size.
A legal minimum gillnet mesh-size of 150mm was first adopted in 1975 and is still current. This is designed to complement the legal minimum lengths. A maximum mesh-size for the fishery of 165mm took effect from 1 January 1997. This is designed to discourage fishers targeting pregnant and other mature school sharks.
Closed areas to commercial gillnetting in inshore waters of Tasmania have been variously implemented since 1954 to protect new-born and juvenile school sharks on nursery areas. A more extensive closed area was adopted during 1988 when all Victorian proclaimed waters (inside 3-mile limit) were closed to the use of shark gillnets and longlines. There are several marine parks and reserves in southern Australia where shark fishing is prohibited. Most of these are in State proclaimed waters.
4.3 Catch/quota allocation
So far the fishery has been managed through input controls. AFMA's preferred method of management is through output controls and following a review of management options for the fishery (FERM 1997), it has set early 1999 as the goal for implementation of Individual Management Quota (ITQ) management. However, through SharkMAC, industry has requested a number of preconditions be met before its adoption (see Section 4.4).
Catch limits on shark bycatch have been imposed in some other fisheries. For example fishers granted Commonwealth Fishing Permits to target scale fish in Commonwealth waters with hooks are limited to a bycatch limit of five school and gummy sharks. In Victorian coastal waters (outside State internal waters) all commercial fishing licences are limited to a shark catch of 50kg of school and gummy sharks.
There are several long-standing major management issues confronting the SSF in the immediate future that are being addressed by SharkMAC and AFMA. These include (1) measures to facilitate the rebuilding of school shark stocks without hampering fishermen targeting more productive and healthy gummy shark stocks; (2) implementation of a management plan under the Fisheries Management Act 1991 and establishment of a single Commonwealth jurisdiction for the fishery that incorporates State coastal waters; and (3), removal of latent effort from the fishery, introduction of Commonwealth fishing concession transferability, and minimization of the flow-on effects to the SSF from management initiatives adopted in associated fisheries.
A revised school shark assessment was prepared during 1996 for the fishery, and SharkMAC and AFMA are continuing to develop appropriate management arrangements for school shark. There is a wide difference in the status of the school and gummy shark stocks and the major challenge is to develop management methods that encourage the rebuilding of school shark stocks while minimizing the impact of these measures on operators who principally target the gummy shark which has healthy stocks.
One of the other major tasks for SharkMAC and AFMA is to develop and implement a new management plan under the Fisheries Management Act 1991. One of the major concerns of managers and industry is the lack of sufficient stability and planning horizons for the fishery to permit operators to make long-term decisions about their involvement in the fishery. This problem will be alleviated through the implementation of a Management Plan for the fishery. Further consideration must be given to lifting the restrictions that have applied on transferability in this fishery since 1986. The major concern in implementing transferability for the fishery is that it may increase effort in the fishery; however, SharkMAC and AFMA have agreed that any form of transferability for the fishery must minimize any increase in effort.
The third issue facing managers is the integration of fishermen currently operating in State waters and those in Commonwealth waters which will place the vast majority of the fishery under a single Commonwealth jurisdiction. Other than Victoria where shark fishing is prohibited in State waters, each State has a large number of operators who take shark on a part-time or opportunistic basis. Whilst the States have implemented management arrangements for their waters which are complementary to those in Commonwealth waters, they are not always identical to those applied by the Commonwealth or in other States. AFMA and the State fisheries agencies are currently identifying the operators who will come under Commonwealth jurisdiction and developing options to integrate State operators.
These last two issues are linked. Much of the latent effort in the SSF arises from the large proportion of operators who are engaged for much of the year in other fisheries, such as the rock lobster fishery. Management changes in these fisheries, like the adoption of quota systems or shortened seasons, could activate latent effort in the SSF. Similarly changes in the relative value of shark and other fishery products could also activate latent effort.
In its December 1989 Policy Statement ‘New Directions for Commonwealth Fisheries Management in the 1990s’ (Anon 1989), the Commonwealth Government viewed the biological problem of overexploitation as being due to an inefficient allocation of economic resources and the absence of exclusive individual rights. Individual Transferable Quotas (ITQs) were identified as the preferred form of management control to prevent over-exploitation and dissipation of potential resource rent (Anon 1989). AFMA considers ITQs to be a highly effective tool for fisheries management and has continued to adopt them as a management regime where appropriate. Such an approach is consistent with AFMA's key legislative objectives of ecologically sustainable development and economic efficiency in fisheries management (Anon 1998b).
A key feature of this arrangement will be the setting of a Total Allowable Catch (TAC) for each of school shark and gummy shark. The TAC will set an upper limit on the annual catch for the fishery and for individual operators through the allocation of ITQs. The AFMA Board has ultimate responsibility for determining TACs but will consider advice from SharkMAC and SharkFAG.
Whilst AFMA has set early 1999 as the goal for implementation of ITQ management through SharkMAC, industry has requested a number of preconditions be met before its adoption.
That establishment of a single jurisdiction under arrangements of the Fisheries Amendment Act 1981 Offshore Constitutional Settlement and implemented on 14 February 1993) be acceptable to Commonwealth licensed shark fishers.
That the Memorandum of Understanding between the Commonwealth and States defining the mechanics of the OCS arrangement be considered and agreed to by SharkMAC.
That the option of continuing some input controls to enhance the harvesting of the school shark stock be retained.
That all school shark catchers, who do not hold an entitlement to take school shark be placed on bycatch limits to restrict their school shark catch as soon as possible.
That the ITQ system cost no more than the total cost industry currently pays for the management of the fishery and be integrated with other ITQ fisheries to receive benefits from economies of scale.
An independent Allocation Advisory Panel be appointed to undertake the quota allocation process.
5. THE MANAGEMENT PLANNING PROCESS
5.1 Provision of resource management advice
Fishery management advice for the SSF has always been provided by one body and research, monitoring and fishery assessment advice has been provided by another. Historically these functions have been coordinated through a management committee or research working groups with representatives from the Commonwealth and southern States. The committees were established under the auspices of the Standing Committee on Fisheries and Aquaculture (or predecessor bodies) which reported to the Ministerial Council on Forests, Fisheries and Aquaculture (or predecessor bodies). However, following the establishment of AFMA, the management advisory role has been adopted by the Southern Shark Management Advisory Committee (SharkMAC) which reports to the AFMA board. SharkFAG provides scientific and stock assessment advice to SharkMAC.
Whilst the early research working groups comprised only Government scientists, SharkFAG comprises Government and industry scientists, fishery managers, economists and shark fishers. SharkFAG holds several 3–5-day meetings each year to review data and update stock assessments. An important element of SharkFAG meetings is the active participation of industry members with their practical fishing experience. They have provided valuable insights into targeting practices, fish movement, stock structure and the validity of the assumptions used in the stock assessments. Research and monitoring of the fishery has been, and continues to be, undertaken by several research agencies. These agencies include State Government research institutes, CSIRO Marine Laboratories, the Bureau of Resource Sciences and the Australian Bureau of Agricultural and Resource Economics.
5.2 Fishery statistics
5.2.1 Methods used for collection of catch and effort data
Shark catch data and some effort data available for the period 1932–56 are collated by Olsen (1959), catch data for period 1957–69 are published in the Fisheries Newsletter by the Commonwealth, and catch and effort data for the period 1970-present are managed in the Southern Shark Fishery Monitoring Database (SSFMDB) maintained by the Marine and Freshwater Resources Institute at Queenscliff in Victoria.
Until 1997, the State fisheries agencies of Victoria, Tasmania and South Australia issued and Collected logbook forms from fishers, partly validated and key punched shark catch and effort data along with data from other fisheries, into the State catch and effort computer databases. These databases are called CandE in Victoria, MAPPER in Tasmania and GARFIS in South Australia. Each year, copies of shark gillnet and longline data from these databases are transferred to the SSFMDB.
Computer validation of the data is undertaken in the SSFMDB to check that forms are complete, codes are valid, and values in selected fields and the ratios of values between selected fields fall within prescribed ranges. This is additional to various checks made in the State databases and is used as a basis for querying fishers on data completeness and accuracy.
The catch and effort data have been collected variously at the resolutions of month, day and shot. In Victoria, the data were collected by month during 1970–72, by day during 1973–78 and by shot during 1978–97. In South Australia, they were collected by day during 1970–72 and as a mixture of month and day during 1973–97. In Tasmania, the data were collected mainly by month. During 1988, a second source of shark catch and effort was introduced in Tasmania to include shot data. These data were not entered into MAPPER, but entered directly into the SSFMDB. In March 1995 this return was replaced by a different shot-by-shot log book.
During 1997 a major change in the data collection process occurred. AFMA introduced a shot by shot log book return (GN01) to collect data from vessels licensed with Commonwealth Fishing Permits and began developing the AFMA database called GENLOG. During early 1997, AFMA issued the GN01 logbook return for vessels engaged in the Non-trawl Sector of the South East Fishery. Vessels licensed with Commonwealth Shark Fishing Permits engaged in both the Southern Shark Fishery and Non-trawl Sector were also issued GN01 logbook returns and required to begin using the new return. Later, during July 1997, remaining vessels licensed with Commonwealth Shark Gillnet Permits or Commonwealth Shark Hook Permits were issued the GN01 logbook return. The GN01 logbook has been issued to 125 operators with Commonwealth Shark Gillnet Permits and to 35 operators with Commonwealth Shark Hook Permits. This logbook covers most of the catch and will reduce the amount of catch passing through the State databases. Nevertheless, it is likely that catches by State-only licensed vessels will continue in the short-term at about the 1997 level, i.e. 477t was produced by 455 vessels without Commonwealth Shark Fishing Permits.
5.2.2 Evaluation of the data collection process
The shark catch and effort data are extremely complex and difficult to merge and manage because they have been collected by the three States using 13 different logbook returns during the period 1970 to 1996. These logbooks have different formats, different spatial (area and depth) and temporal (month, day and shot) resolutions and multiple reporting occurs (i.e. same data reported to more than one fisheries agency). Adequate effort data for gillnets are not available from any State before 1973 or from Tasmania during 1977–87. In all three States the logbook formats and the resolution of the data have been changed several times and all have had different formats concurrently during 1970–97. All logbook returns have had facility to record location of fishing within a grid of 1° of latitude by 1° of longitude, and in some cases within one quarter of the 1° by 1° grid. Only Victorian logbook returns have had facility for recording depth of fishing.
The Commonwealth GN01 logbook return adopted during 1997 has a shot resolution. In addition to facility for recording depth of fishing and fishing location within a grid of 1° of latitude by 1° of longitude, or within one quarter of the 1° by 1° grid, the GN01 return has facility for recording start and finishing positions of each shot.
Data reported by fishers have been checked from time to time against records collected from fish buyers and auctioneers but this has not been comprehensive or systematic. Systems currently being implemented by AFMA for reporting of catches prior to the vessels entering port and proposed docketing systems required for the implementation of quota management will improve the timeliness, completeness and quality of the data.
5.2.3 Data processing and storage and accessibility
The SSFMDB is a database developed under the Scientific Information Retrieval Database Management System. Initially developed at the Marine and Freshwater Resources Institute (MAFRI) during 1986 (Gason and Walker 1991), this system has been continually modified to cater for changing logbook returns and demands for data. The system has also been gradually upgraded to take advantage of improvements in computer hardware and software. These enhancements have enabled improved data accessibility, validation and audit checks. Modifications to the SSFMDB began during 1997 in preparation to receive data from the Commonwealth GN01 logbook return.
After loading data from the State databases, the SSFMDB provides additional data validation, correction for multiple reporting from fishers, standardization of landed catch weights, and reporting of data summaries for management, licensing, monitoring and stock assessment purposes. Landed catch weights of sharks are standardized to ‘untrimmed carcass weight’ (i.e. headed and gutted shark with all fins attached) whereas weights of scale fish taken by shark gillnets and shark longlines are standardized to live weight. In addition, the SSFMDB can weight for missing data and can, through date of landing and vessel distinguishing mark, match catch, fishing gear and fishing locality from the logbook data with commercial catch sex-length-frequency data and ageing data from vertebral samples collected ashore.
The SSFMDB provides up-to-date catch and effort data summaries and data files essential for management, stock assessment and licensing. High-level data summaries are required by AFMA, other fisheries agencies associated with management of the fishery, SharkMAC and SharkFAG. Detailed files of data on shot, daily and monthly bases are required by SharkFAG for stock assessment purposes. Data on a vessel and fisher basis are required by AFMA and licencees for establishing fishing histories and access rights, and by the Australian Bureau and Resource Economics for economic survey purposes. There is also a need for rapid response to requests for additional data extractions and validation by SharkFAG and to ad hoc requests for data files and data summaries by AFMA, SharkMAC, SharkFAG and other agents acting on behalf of AFMA.
The commercial confidentiality of data provided by fishers and fish processors is protected by reporting data summaries for statistical fishing cells, or fishing ports, when the catches are taken from five or less fishing vessels. A pseudonym is used when providing data at the level of fishing vessel for research purposes.
5.3 Stock assessment
5.3.1 History of assessments in SSF
Olsen (1954) drew attention to the slow growth rate and low reproductive capacity of school sharks and stressed the need to safeguard the recruitment processes of the stock. He recommended (1) protection of pregnant sharks during the 2-months prior to birth, (2) declaration of known ‘pupping’ areas as sanctuaries for young sharks, and (3) adoption of legal minimum lengths. Later Olsen (1959) argued that the life history characteristics of school shark makes the stock vulnerable to the effects of heavy fishing and drew attention to the collapse of the Californian soupfin fishery during the 1940s which at the time was believed to have been closely related to the school shark of southern Australia and is now classified as the same species. He further argued that the school shark stock should be compared with sea mammals, such as whales and seals, rather than the stocks of the more fecund and faster growing teleost and invertebrate species. While Olsen (1959) was careful to point out that the data for school shark did not show that the population was depleted, he believed there was sufficient evidence to ‘discuss measures to conserve the stocks in order to maintain a maximum steady yield’. He presented evidence of a decline in abundance of juvenile sharks in the inshore waters of Port Phillip Bay in Victoria during 1943–54 and of Pittwater and Port Sorell in Tasmania during 1948–52. He also showed a decrease in catch per hook, a decrease in the mean landed weight of sharks, an increase in the amount of gear carried by each fishing vessel, and a change from an inshore to an offshore fishery involving increases in distances travelled from port.
During the late 1960s and early 1970s, a series of quantitative assessments were undertaken based on CSIRO tagging data. Advice to the fishery managers from these assessments varied according to the scientists' acceptance of various assumptions underlying the data analyses. Opinion varied on likely biases in estimates of fishing mortality and natural mortality caused by initial tag mortality, loss of fin tags and under-reporting of recaptured tagged sharks. Apart from one analysis which included reproduction parameters of school shark, most of these early assessments were based on the Beverton and Holt yield per recruit analysis which depended on the assumption that recruitment was independent of stock size.
By the early-1970s there was general concern that the school shark stock was being depleted. However, the ban on the sale of large school shark in Victoria during 1972–85, and the switch in targeting from school shark to gummy shark coinciding with the switch from predominant use of longlines to predominant use of gillnets in Bass Strait alleviated much of this concern. Hence much of the interest in stock assessment also switched from school shark to gummy shark.
The first stock assessment for gummy shark was undertaken by walker (1977) based on (1) catch per unit effort trends, (2) a yield per recruit analysis which was extended to in corporate information on reproduction, and (3) an alternative equilibrium model developed by Holden (1974). This equilibrium model incorporated parameters for growth rate and the peculiarities of shark' reproductive biology for estimating the maximum total mortality a shark population might with stand before affecting recruitment. However, the weakness of the model was that it did not include density-dependent regulation. It was generally accepted at the time of this assessment that there was a need to limit effort and the number of vessels in the fishery.
This assessment, and later assessments, were complicated by the effects of gillnet mesh selectivity. Earlier assessments had been free of this complication because until the early 1970s most sharks had been caught on hooks. On hooks, all sharks of length longer than the legal minimum length are equally vulnerable to capture, but in gillnets, sharks of different size are not equally vulnerable. Small sharks swim through gillnets but become progressively more vulnerable to capture as they grow. After reaching the length of maximum vulnerability sharks then become progressively less vulnerable as they tend to be deflected from the nets because their heads cannot so readily penetrate the meshes (Kirkwood and Walker 1986). Other difficulties identified with the stock assessments included the use of catch-per-unit-effort (CPUE) as an index of relative abundance of stocks, stock structure and distribution, the movement patterns of the sharks and the effects of using fixed growth, fecundity and natural mortality parameters values independent of stock size.
These issues were addressed through a series of eight scientific workshops held during 1983– 91 by the Southern Shark Research Group which reported to the former Standing Committee on Fisheries (predecessor of the current Standing Committee on Fisheries and Aquaculture) through the former South East Fisheries Research Committee. Each workshop ran for several days and was attended by fisheries scientists from the Commonwealth, Victorian, Tasmanian, and South Australian fisheries agencies and by fisheries scientists with special expertise in fisheries population dynamics or shark biology. These workshops reviewed data, data analyses, and research and monitoring proposals, and provided scientific advice on conservation of the stocks.
The early workshops considered Schaefer biomass dynamics analyses of gummy shark and school shark and DeLury estimates based on stock reduction, Deriso delay-difference and Beverton and Holt yield-per-recruit analyses of gummy shark (see Walker 1986). Although various adaptations were made to the models, it was generally agreed that either gillnet selectivity or the peculiarities of the sharks' biology did not satisfy many of the assumptions of these models (Walker 1986). It became clear that special models had to be developed for the SSF for more rigorous assessments.
Walker (1986) developed a dynamic pool model to incorporate the length-selective mortality of gillnets and, following Holden (1974), included the peculiarities of shark reproduction. Based on the results of analyses from this model, trends in CPUE and life history characteristics of sharks, following the Third Southern Shark Assessment Workshop held during April-May 1986, the Southern Shark Research Group recommended that fishing effort be reduced to 1982 levels and that the development of new modelling and assessment techniques appropriate for gummy shark and school shark be undertaken as a matter of high priority.
Density-dependent regulation was subsequently incorporated into the model by assuming natural mortality of various juvenile age-classes varied with biomass or stock number in all, or selected, age-classes (see Prince 1991; Walker 1991, 1992). This became the model underlying the specially developed computer graphics package ‘Sharksim’ for simulating the fishery (Sluczanowski 1991; Sluczanowski et al. 1992). Using a general computer software framework initially programmed by C.J. Walters (University of British Columbia) and subsequently adapted by N. Hall (Western Australian Marine Research Laboratories), Prince (1991) used a range of parameter values for catchability, natural mortality, and initial biomass, and compared catches predicted by the model with catches reported by fishers. All initial assessments assuming single stocks with these models indicated that both gummy shark and school shark were severely depleted. More optimistic scenarios could be produced where the stocks were divided into regional substocks.
During February 1991, following the Fifth Southern Shark Assessment Workshop, the Southern Shark Research Group concluded that the stocks had been depleted to levels where catches of only 650 and 550t, untrimmed carcass weight, could be sustained for gummy shark and school shark, respectively. However the Group stressed that there was a high degree of uncertainty associated with these estimates.
Subsequent separate stock assessments of gummy sharks in Bass Strait and waters off South Australia based on revised parameters estimates for growth and reproduction, and where natural mortality and catchability were estimated by the model, gave much more optimistic outlooks for the fishery (Walker 1993b, 1994a,b). Smith (1993) obtained similar results when he reviewed this work and then applied a stock depletion model developed by Francis (1992) and the biomass dynamics model developed by Fox (1975).
Consequently, when the Southern Shark Research Group met in March 1993, it revised the estimate of sustainable catch for gummy shark from 650 to 1250t, untrimmed carcass weight - 800t for Bass Strait, 200t for Tasmania, and 250t for South Australia. The Group reiterated its recommended catch of 550t, untrimmed carcass weight, for school shark. These recommendations represent reductions to the current catch of gummy shark of about 40% across the fishery and reductions to the current catch of school shark by more 50% across the entire fishery.
SharkFAG, established by the newly formed AFMA, replaced the Southern Shark Research Group and held its inaugural meeting on 11 October 1993. SharkFAG's one assessment of gummy shark in 1995 remains current. Most of SharkFAG's efforts have been devoted to improving the school shark assessments. SharkFAG's 1995 assessment was based on Schaefer production and delay-difference models.
For the 1995 school shark assessment raw fishing effort data were standardized through a generalized linear model with raw CPUE as the dependent variable and year (1973–93), region (Tasmania, Bass Strait, South Austrialia, and Western Australia), and gear type (hooks and 6,7 and 8-inch mesh-sizes of gillnets) as the independent variables. Model assumptions were that errors in raw CPUEs follow independent, identical log-gamma distributions (Xiao 1995a). SharkFAG concluded that there are problems standardizing for the effects of gear type. This is partly because the gears take different components of the population (e.g. gillnets of 7-inch mesh-size tend to take larger sharks than gillnets of 6-inch mesh-size). These problems, along with the relatively short period of available effort data (from 1973 to the present), compared with catch data which cover the entire period since the shark fishery began, reduce the varacity of biomass dynamics and dely-differnce models.
Xiao (1995a) undertook a stock assessment of school shark applying the Schaefer production model. The model was applied in a difference form by assuming that errors in the catches follow independent, identical log-normal distributions for a range of intrinsic rates of population growth, r (0.01 to 0.10 by 0.01 yr-1). Catch data for the period 1930–93 and target fishing effort for the period 1973–93, standardized by Xiao (1995b), were applied and forward projections from the model were provided for the period 1994–2045. Initial biomass, B1930, was assumed to equal the environmental carrying capacity. Thus, 11 sets of initial biomass, B0, and catchability coefficient, q, were estimated and used, by bootstapping, to simulate 1000 sets of catch to project future levels of biomass in a risk analysis. The assessment indicated that the biomass dropped from its initial biomass in 1930 through about 50% of inital biomass in 1973 to about 25% of inital biomass in 1993. The risk analysis suggests that if the future level of catch is maintained at the current level of C1993=1889t live weight, the level of biomass would continue to decrease. It was concluded that fishing effort, as translated into net catches, not be increased beyond the current level, and, if possible, should be reduced.
Walker (1995b) undertook a stock assessment of school shark applying the delay-difference model derived by Deriso (1980) and elaborated by Schnute (1985, 1987). The model requires a time series of catch and effort data and can either use or estimate natural mortality, catchability, Brody growth and stock-recruitment parameters. In this assessment exogenous parameter estimates for natural mortality and the Brody growth parameters were entered into the model and the model was used for estimating catchability and the two Beverton and Holt (1957) stock-recruitment parameters. Catch data for the period 1930–93 and target fishing effort for the period 1973–93, standardized by Xiao (1995a), were applied and forward projections from the model were provided for the period 1994–2050. Both sensitivity and risk analyses were performed.
The delay-difference model has the advantage over the biomass dynamics models in that it incorporates biological information while having fewer parameters than many of the other potentially over-parameterized age-structured models. The disadvantages of the model for a school shark assessment are that it does not incorporate all available information on reproduction and it assumes ‘Knife-edge selection’. The model predicted that the stock was reduced to 15–25% of initial biomass and that recruitment was stable and the stock could stabilize at the level of fishing effort during the early 1990s. Although uncertainly about the form of the stock-recruitment relationship increases uncertainties in forecasting, risk analyses with best estimates of key population parameters suggest rebuilding the stock to 30–40% of initial biomass within 15 years would require reductions in fishing effort to below half the current level.
5.3.2 Measures of stock abundance
The main measure of stock abundance used is catch per unit effort obtained from mandatory fish catch and effort returns submitted by fishers. Although catch is available since the beginning of the fishery (i.e. 1927–97), fishing effort data and hence catch per unit effort data, are currently readily available only for the period 1973–97 (Walker et al. 1998b) (see Section 5.2).
Sex and partial length measurements from shark landings to provide sex-length-frequency composition data for the landed catch have been collected in Victoria for the period 1970–97 and in South Australia for the periods 1973–76 and 1986–97. Less continuous data have been collected in Tasmania (Walker et al. 1998c). Length-at-age data for males and females separately are available for gummy sharks sampled from Bass Strait during the periods 1973–76 and for both gummy shark and school shark sampled from Bass Strait and South Australia during 1986–87 and 1990–1993. Ideally length-at-age data are collected annually (Walker et al. 1998c).
The length-at-age data have been combined with the time series of length-frequency and catch and effort data to produce time series of catch-at-age and effort data which have been used in catch-at-age analyses for estimating mortality and recruitment. These analyses have been used to estimate mortality of gummy shark (Walker 1986, 1992).
The length-at-age data have also been combined with length-frequency composition data to contribute to the validation of the gummy shark model. The data will eventually be used in more complex age-structured models. These data provide trends in sex and length-frequency composition of the catch and can be applied in various fishery assessment models. Mean length or mean weight of gummy sharks in the catch have been determined from the length-frequency data and used in SharkFAG's 1995 gummy shark stock assessment model for estimating mortality parameters (Walker 1994a, 1994b). The length-frequency data could be used directly in length-structured models, but so far they have not been used for this purpose.
SharkFAG is currently exploring the feasibility of adopting fishery-independent surveys for providing a time series of indices of relative stock abundance. A pilot survey undertaken during late 1998 will provide the basic data required to design a full-scale survey whereby selected vessels would be engaged to undertake fishing with a standard set of gillnets at selected fixed-sites at a particular time of the year. The pilot survey will provide data on inter-shot variability as a basis for determining the number of sets of the gear needed to give sufficient statistical power to detect changes in annual catch rates over time at various levels of probability. The pilot survey will also help determine appropriate spatial distribution of the sets and the cost of such a survey.
A similar fixed-site sampling scheme was undertaken in Tasmania by CSIRO during 1991–97 and in Victoria by MAFRI during 1994–97 to provide abundance indices of newborn and young juvenile sharks in school shark nursery areas. Variance in the catch rates was found to be too high to detect a change in abundance from year to year during the sampling periods. Whilst the data will provide valuable baselines for future comparisons, the approach is considered impractical for monitoring pre-recruits (Stevens and West 1997).
The stock assessments in the SSF have depended on time series of catch and CPUE. The CPUEs were initially used as raw CPUEs and then attempts were made to separate fishing effort targeted at gummy shark from fishing effort targeted at school shark. More recently the data have been statistically standardized to avoid effects of differences in fishing power of vessels, season and region. For the purpose of display, the data are presented for three separate regions for each fishing method and each mesh-size for the gillnet method. The three zones are refered to as Bass Strait, South Australia and Tasmania and refer to waters on the continental shelf and continental slope.
Bass Strait is defined as waters bounded by the Victoria coastline, the north coast of Tasmania and by latitude 41°S to the west and to the east of Tasmania. Tasmania is defined as waters south of latitude 41°S South Australia is defined as waters off South Australia.
Gummy shark total catch during the 25-year period 1973–97 is 66% (67% in 1997) from Bass Strait, 25% (26% in 1997) from South Australia and 9% (7% in 1997) from Tasmania. In Bass Strait, 81% of the gummy shark catch was taken by 6-inch mesh-size, 1% by 61/2-inch mesh-size, 8% by 7-inch mesh-size and 10% by hooks, whereas in South Australia 10% was taken by 6-inch, 12% by 6 1/2-inch, 56% by 7-inch, 12% by 8-inch and 10% by hooks. Total school shark catch during 1973–97 is 37% (33% in 1997) from Bass Strait, 45% (52% in 1997) from South Australia and 18% (15% in 1997) from Tasmania. In Bass Strait, 72% of the school shark catch was taken by 6-inch mesh-size, 1% by 61/2-inch mesh-size, 4% by 7-inch mesh-size and 22% by hooks, whereas in South Australia 10% was taken by 6-inch, 5% by 61/2-inch, 56% by 7-inch, 17% by 8-inch and 11% by hooks.
Trends in catch (Figure 4), fishing effort (Figure 5), catch per unit effort for gillnets and catch per unit effort for hooks (Figure 6) are presented for gummy shark and school shark, for the Bass Strait Zone and South Australia Zone. These trends for gillnets are given for each mesh-size separately. Appropriate data are not available to present similar information for the Tasmanian Zone. In Bass Strait, gillnets of 7-inch mesh-size were the main method used during the early 1970s but since 1976 most of the catch of both gummy shark and school shark from Bass Strait has been taken by gillnets of 6-inch mesh-size. In South Australia, on the other hand, most of the catch of both species has been taken by gillnets of 7-inch mesh-size (Figure 4). Fishing effort has declined markedly in both zones since adoption of the Southern Shark Fishery Management Plan in 1988. With the general decline in both 7-inch and 6-inch gillnet effort in South Australia, the relative importance of the 6-inch mesh-size is rapidly increasing (Figure 5). Catch per unit effort for gillnets and for hooks (Figure 6) show marked increases for both gummy shark and school shark in Bass Strait but no increase in South Australia since introduction of the Management Plan. The trends in South Australia, however, appear to be stabilizing.
5.3.3 Biological advice review process
SharkFAG, which is comprised of shark biologists, fishery modellers, shark fishers, an economist and the manager of the SSF, undertakes the assessments. Although there are no prescribed review processes in place for external review of the assessments, specialist fishery modelers from Australia and overseas have been engaged from time to time to provide advice or to review an assessment (e.g. see Section 188.8.131.52).
5.3.4 Biological management reference points
From limited early discussions, SharkFAG believed that the biomass of each of the major species in the fishery should not fall below 40% of initial biomass. It was considered that this should provide and adequate safety margin for shark species, which tend to have lower fecundity than telcost and invertabrates. More recently, as a result of dialogue between SharkFAG and SharkMAC, when revising and improving the school shark assessment, risk has been expressed in terms of the probability of the mature biomass being below current biomass levels in 15 years in the future under alternative harvest strategies. In this regard, SharkFAG intends to review the issue of biological management reference points.
5.3.5 Sustainability of the resource
184.108.40.206 Gummy shark assessment
The current gummy shark assessments undertaken by SharkFAG during 1995 assume a separate stock for each of the three zones of Bass Strait, South Australia and Tasmania defined above. The Bass Strait assessment indicates that the current biomass level of gummy shark in this zone is between 40% and 55% of the initial biomass level. Various analyses indicate that recruitment of juveniles to the Bass Strait fishery has been relatively stable for the last 20 years, despite large variations in fishing effort over this period (Walker 1994a,b; Prince 1994).
Catch of gummy and school shark by method and region during 1973–97
Fishing effort by method (and mesh-size) and region during 1973–97
Catch levels of gummy shark in Bass Strait since 1973 (when it was 1361t, untrimmed carcass weight) have varied from a low of 738t in 1979 to a high of 1272t in 1992. The catch was 1239t in 1993 (Figure 4). While there is some variation in the annual availability of recruits, the apparent long-term stability in levels of recruitment indicates that the current catch levels are sustainable. CPUE decreased during the 1970s and into the 1980s but increased markedly since 1987. This is probably due largely to management measures which reduced fishing effort in Bass Strait by a third (Figure 5), but the large increase during 1992 and 1993 (Figure 6) is likely to be due in part to annual variability.
Analysis of the effects of mesh-size of gillnets on sustainable yields from the Bass Strait component of the gummy shark fishery indicates that 6-inch mesh-size provides a marginally higher sustainable yield than 7-inch mesh-size. Both the 6-inch and 7-inch mesh-sizes provide much higher sustainable yields than either 5-inch or 8-inch mesh-sizes (Walker 1998a).
The South Australia assessment indicates that the biomass of gummy shark in this zone is between 40% and 50% of the level before fishing began. Despite no new assessment being available, the SharkFAG considers that the changes in understanding of the status of gummy shark in Bass Strait may be relevant to understanding the stocks in South Australia. The dominant mesh-size of gillnets in South Australia has been 7 inches but this has been reduced to 61/2 inches since 1 January 1997. This may enable more effective targeting of gummy shark in regions that have been previously only lightly exploited, particularly west of Port Lincoln. The potential for increased catches is unknown at present.
The Tasmanian Zone has a lack of accurate long-term effort data and this prevents a detailed assessment in the short-term. The catch of gummy shark in the Tasmania zone has averaged 9% of the total gummy shark catch during 1973–97 and remains at about this level.
CPUE for gummy and school shark by method and region during 1973–97
220.127.116.11 School Shark assessment
Deficiencies of the Schaefer production and delay-difference models adopted for the 1995 assessment led SharkFAG to favour age-structured models. SharkFAG is now of the view that the soundest approach to school shark stock assessment is to adopt fully age-structured models that incorporate the peculiarities of shark biology, the selectivity of the fishing gear, the movement patterns of the sharks and the use of spatially-disaggregated data. In proceeding with this approach SharkFAG is addressing the dificiencies of the 1991 assessment which was also based on an age-structured model. The deficiencies of the 1991 assessment include the lack of a statistically-based method to fit the adopted model to the data, use of unstandardized CPUE data and inadequate consideration of uncertainty.
SharkFAG completed an assessment during April 1996 (Southern Shark Fishery Assessment Group 1996a) which was subsequently reviewed by R. Deriso of the Inter-American Tropical Tuna Commission. The purpose of the review was to provide SharkMAC and the AFMA Board with independent advice on the adequacy of the data and methods used, and whether the results of the stock assessment provide an adequate basis for management decisions. Dr. Deriso completed his review during August 1996 and supported SharkFAG's conclusion that a reduction in the catch of school shark is required. Dr. Deriso did however suggest improvements that could be made both to the current assessment and to the longer-term research programme (Deriso 1996). SharkFAG incorporated his suggestions into the assessment and used it to evaluate a number of scenarios that involve phasing in any required reductions in catch. This revised assessment was presented to SharkMAC during November 1996 (Southern Shark Fishery Assessment Group 1996b) and henceforth will be referred to as the 1996 Assessment. Details of model structure, parameter values and risk analyses are given in Punt and Walker (1998). Key findings of the assessment are as follows.
The median of the posterior frequency distribution for the size of the mature biomass of the school shark resource at the start of 1995 is estimated to lie between 15% and 46% of the unfished level.
Despite the uncertainty in these biomass estimates, catches have been substantially larger than the estimates of MSY.
There is a high probability that current effort will lead to further reductions in population size. To achieve the objective that there be an 80% probability that mature biomass is above the 1996 level of mature biomass in 15 years time, a catch reduction of around 35% will be required.
It is possible to phase-in the required reductions, however this will result in a lower long-term sustainable catch.
18.104.22.168 Uncertainties in the assessments
One of the greatest uncertainties in the assessment of both species, particularly gummy shark, surrounds the spatial structure of the populations. The issue of single versus regional stocks is complicated and cannot be resolved in the short-term. Current genetics and tagging studies are addressing this uncertainty.
The 1995 assessment of gummy shark attempted to take account of this spatial structure by partitioning the available data. Two separate stocks or substocks were assumed, one in Bass Strait and the other in South Australia (data around Tasmania south of 41°S were excluded due to an inadequate time series of fishing effort data). Differences in CPUE trends between gillnets and hooks and between different mesh-sizes of gillnets are not easily explained. The significance of natural refuges such as areas not fished because of rough terrain or refuges created by closed areas cannot be easily evaluated.
The 1996 assessment for school shark examined alternative hypotheses and SharkFAG identified several factors that could substantially affect the results. Some of these have been identified because SharkFAG has attempted to examine a broader range of modelling hypotheses than is commonly the case.
The results are highly sensitive to the selection of a method for standardizing the catch and effort data. In particular, the results depend markedly on whether a log-normal or Poisson error-model is used, and how zero catches are handled (Punt et al. 1996). None of the analyses conducted by SharkFAG currently permit discrimination among the alternatives, so SharkFAG advised that these should be considered to be equally likely. Another factor which may affect these results is assumptions about movement. The group identified several distinct types of movement: (1) vertical movement, which results in a possibly substantial fraction of the population being unavailable to the fishing gear at any one time, (2) movement between close inshore and offshore, (3) movement to and from New Zealand, and (4) movement across the fishery itself. These issues can only be dealt with using a fully spatially-structured population dynamics model for the SSF.
The majority of the model predictions are based on the assumption that fishers who use 7-inch and 8-inch mesh-size changed to 61/2-inch mesh-size from 1 January 1997. This has been implemented by assuming that these fishers will continue to target shark in the way they have in the past. This assumption seems to be the ‘best’ possible at present but will be violated to some extent because of the differences among the various regions withing the fishery.
The results of the stock assessment are highly imprecise if no constraints are placed on the parameter that determines the productivity of the resource (MSYR—the fraction of the biomass that can be taken at MSY). This is a consequence of the uninformative nature of the catch and effort data for this species. The alternative probabilities assigned to different values of MSYR reflect a consensus within SharkFAG based on estimates for other shark species and intuitive judgements. These probabilities are the best currently possible, but may be substantially in error. Information is lacking about productivity for most shark species, so making inferences about likely ranges in MSYR for school shark is exceedingly difficult.
SharkFAG attempted to specify the full range of plausible modelling hypotheses. Although the hypotheses specified cover a wide spectrum, there are probably several hypothese that were not identified but are nevertheless plausible. Furthermore, it was impossible, due to time and data constraints to consider all of the hypotheses quantitatively. Some of these hypotheses (e.g. the degradation of some historical pupping grounds) could have a substantial impact on long-term population projections.
22.214.171.124 The manager's perspective
The fishery managers, the industry and the scientists are all integrally involved in the management process of the fishery, assessment of the stocks, harvest strategy evaluation and setting of research priorities. Through these processes there is a general concensus that the gummy shark stocks are sound and the school shark stocks are markedly depleted. This has led to the current situation where the emphasis is on improving the school shark assessment and managing the fishery in a way that will first arrest the current trend of declining biomass and then begin a rebuilding of the stock. Hence, from the fishery managers' perspective there has been a need to focus on stock assessment and harvest strategy evaluation for school shark.
Fishery managers need stock advice that is scientifically defensible, up-to-date and accepted by the industry and the community. This has been achieved for school shark through a transparent process of stock assessment and management involving representative participation and consultation with all the key stakeholders. Stock assessments have gained scientific credibility through the active participation of sevearl government and industry scientists and a favourable review by a non-Australian scientist.
Although less urgent the fishery managers need similar assessments undertaken through similar processes for gummy shark and the minor species such as saw shark and elephant fish. The managers also need an evaluation of bycatch, discards and fishery interaction with mammals, birds and other fauna.
126.96.36.199 The user's perspective
The school shark assessment has had active input from industry, which has given them a first-hand view of the inputs, assumptions and associated uncertainty. Various views of industry and the scientists have been formulated as alternative hypotheses and tested as part of the uncertainty analysis of the assessment. This has all contributed to raising the credibility to the assessment in the eyes of industry.
The shark industry is complex in its diversity. Most shark fishers use gillnets while others use hooks, and while most target gummy shark, others target school shark. Also, while some fishers are involved in the SSF on a full-time basis with maximum gear entitlements, others are involved on a part-time basis with less gear entitlements. This has resulted in a number of separate sectors in the industry.
Differences between sectors in the fishery have created tensions. Allocation of gear entitlements on the basis of documented historical catches led to numerous appeals during the gear allocation process. Differences in gear allocation and differences levels of participation, or representation, for the various sectors in the consultative processes have at times led to dissatisfaction by some users of the resource. Most attempts by the managers to reduce fishing effort have been resisted by industry through the consultative processes.
188.8.131.52 Evaluation of the management process
The current management processes are necessary and work. There is an ongoing need for stock assessment, harvest strategy evaluation, structural readjustment of industry, consultation and evaluation of the effectiveness of changes. Through these processes one-third of the fishing effort has been removed from the fishery, the economic viability of the industry has been markedly improved and the decline in school shark biomass is biomass is being arrested. Despite these positive outcomes, some do regard the processes as time consuming and costly.