R. Melville-Smith1, R. Gould2 and L. Bellchambers1
1 Department of Fisheries, Western Australian Marine Research Laboratories
P.O. Box 20, North Beach WA 6920, Australia
2 Department of Fisheries
3rd Floor Atrium, 170 St George's Terrace
Perth WA 6000, Australia
In Western Australia several large crab species occur in the offshore waters. However, only three, the giant crab, (Pseudocarcinus giga), the champagne crab (Hypothalassia acerba) and the crystal crab (Chaceon bicolor) are of commercial importance.
The biogeographical boundary separating the cool water of the south coast of the state from the warmer waters of the west coast has provided a logical boundary between crustacean fisheries in Western Australia (Figure 1). These fisheries are managed as the South Coast Deep Sea Crab Fishery (SCDSCF) and the West Coast Deep Sea Crab Interim Managed Fishery (WCDSCIMF). Permit holders in the West Coast Deep Sea Crab Interim Managed Fishery are entitled to take champagne, giant and crystal crabs but not rock-lobsters. The WCDSCIMF operates along side Australia's largest rock-lobster fishery, the West Coast Rock-lobster Managed Fishery (WCRLMF), where fishing generally occurs in 0–200 m. Although managed separately licencees in the WCRLMF are permitted to retain 12 deep-sea crabs, primarily champagne crabs, per day per boat. On the other hand, licencees in the South Coast Deep Sea Crab Fishery are entitled to take champagne, giant and crystal crabs and as a result of the licensing framework surrounding the development of this fishery most fishers are also entitled to take southern rock lobster (Jasus edwardsii).
The Department of Fisheries have records of various fishers from the 1960s, 1970s and 1980s expressing interest in establishing commercial fishing operations based on champagne, giant and ‘deep-sea crabs’ on the west coast. Although most of these proposed ventures did not go any further, some small-scale exploratory fishing targeting champagne crabs by rock-lobster fishers was undertaken between 1985 and 1990 with some rekindled interest in the 1990s. Champagne crab catches peaked between 30 and 45 tonnes from 1997 to 1999, before decreasing to negligible levels (<100 kg) from 2001onwards. The decrease in catches was in part due to a decline in champagne crab stocks, however low beach prices and increased interest in the more valuable crystal crab also contributed (K.Smith, Murdoch University, Australia, pers. comm.). Therefore, on the west coast, management of giant and champagne crabs is primarily focused on ensuring biological sustainability and maintaining breeding stocks of the species rather than developing a viable commercial fishery.
Crystal crabs have only been targeted on the west coast since the late 1990s and the WCDSCIMF is now almost entirely dependent on the size and productivity of the crystal crab resource.
Map of the W.A. coastline showing the crystal crab management zones and depth contours between 500–1000 m
Both giant and champagne crabs landings have been larger and more regular in the South Coast Crustacean Fishery than on the west coast. Since 1990 the combined giant and champagne crab catch has, in most years, been in excess of 30 tonnes, with occasional annual catches reaching 40 to 50 tonnes. In the past, crystal crabs have not formed a significant contribution to the South Coast Crustacean Fishery, apart from one year (2002) when over 10 tonnes were landed before a moratorium was placed on targeting the species pending further research. The size and distribution of the fishable stock in this region is unknown.
In 1991 it was recognized that with increasing interest in deep-sea crabs of all species there was a need to move to more formal management. In January 1992 following a request for expressions of interest, the Minister for Fisheries issued a press release announcing that by 1 April 1992 a plan would be in place to develop the fishery. This resulted in more than 80 expressions of interest for endorsements to take deep-sea crabs outside the rock-lobster fishery. In response, in June 1993, 53 endorsements were approved (49 on the south coast and four on the west coast). A one-tonne catch per year minimum performance criteria was placed on each approved vessel. Following a review of these allocations, in May 1993 a further three endorsements were granted on the west coast. In 1992 a commercial fisherman working in cooperation with the Commonwealth Scientific and Industrial Research Organisation (CSIRO, Hobart, Australia) conducted some limited research fishing. The fishing focused on champagne and giant crabs, but was of limited success due to the size of the fishing vessel used and lack of gear suitable for fishing in depths greater than 150 m.
New complexities were introduced into the management of both the SCDSCF and WCDSCIMF when permit holders realized the potential quantities of crystal crab available and the species' commercial value. The dilemma is one that besets the managers of many new fisheries: i.e. on one hand faced with a previously unfished resource that has a potentially long term yield, together with an industry geared up and keen to exploit it; while on the other hand having no catch history, biological information, or information on the spatial extent of the fishery. Given the current focus in Western Australia on the exploitation of crystal crab, this paper deals only with a description of crystal crab catches on the west and south coasts of Western Australia and the proposed management of this resource.
Crystal crabs belong to the family Geryonidae. Other members of this family are widely distributed on continental shelves throughout the world, generally occurring in depths between 200–1200 m (Hastie 1995). Over the years there have been several fisheries in various locations for deep-water crabs of this family, e.g. the north eastern coast of North America, the central and southern coasts of the South American east coast, the west coast of Africa, the east coast of southern Africa and the Gulf of Mexico. Only the Chaceon (previously called Geryon) fishery off Namibia, on the west coast of southern Africa, has produced large catches (5 000–10 000 tonnes a year) over a sustained period (Melville-Smith 1988). However, even landings in that fishery have decreased to 20% or less of what they were during their peak (Haufiku, Namibian Fisheries Department, Swakopmund, Namibia, pers. comm.). One of the primary reasons for the lack of sustainability of these fisheries is that the crabs live in cold unproductive waters (generally 3–8° C) and are slow growing and long lived making them vulnerable to overexploitation.
Crystal crabs occurring off the Western Australian coast are considered at this stage to be Chaceon bicolor, a species which is also found in the central Pacific from the Emperor Seamount Chain to eastern Australia (Manning and Holthuis 1989) and along the west and north coast of Australia (Jones and Morgan 1994). At this stage Chaceon appears to have a wide distribution, although some systematics experts have suggested that further work may show that the pale coloured specimens found off the Western Australian coast are a different species to the purple, tan and yellowish coloured specimens of C. bicolor found in the Pacific. The depth distribution of Chaceon species is reported to be between 275 and 1 600 m (Manning and Holthuis 1989). However on the Western Australian coast the species has only been reported in commercial catches from 450 to 1220 m (Lance Hand, Bellenden Nominees, Geraldon, Australia, Western Australian Museum records).
2. INTERIM MANAGEMENT CONTROLS IN WESTERN AUSTRALIA'S CRYSTAL CRAB FISHERIES
2.1 The West Coast
Until 1995 the take of deep-sea crabs seaward of the 200 m isobath was the responsibility of the Australian Commonwealth Government and some 22 vessels were licensed by the Commonwealth to fish for deep-sea crabs in Commonwealth managed waters off Western Australia. However, under the Offshore Constitutional Settlement Agreement of 1995, and on the basis of the links with the State managed rock-lobster fisheries, management of deep-sea crab fisheries became a State Government responsibility.
The fishery for crystal crabs began in 1997–1998 when one fisher undertook exploratory fishing for deep-sea crabs on the west coast between 34° 24' and 22° 19 S' in depths of 540 to 1080 m. The promising catches of crystal crabs by this exploratory fishing trip generated more interest in commercially exploiting this fishery on the west coast and by the end of 1999 the catch had increased to almost 25 tonnes.
The fishery was originally open to all 595 West Coast Rock-lobster fishers as the fishery had historically taken small quantities of deep-sea crab (mainly champagne crabs) as byproduct in their rock-lobster traps. However, to take deep-sea crabs out of the rock-lobster fishing season (15 November to 30 June) a specific fishing boat licence endorsement was required. In April 1999, 26 vessels on the south coast and six vessels on the west coast had acquired these licence endorsements as a result of earlier interest and activity related to deep-sea crabs.
The need to more formally manage these fisheries arose in 1998 in addressing reporting requirements that Environment Australia proposed to impose as a condition of export approval under Section 10A of the Wildlife Protection (Regulation of Exports and Imports) Act 1982. The downturn in the Asian economy and concerns about its impact on rock-lobster export prices also resulted in increased targeting of deep-sea crabs by rock-lobster fishers during the 1998–1999 rock-lobster season and increased interest from rock-lobster fishers wanting to target deep-sea crabs outside the rock-lobster fishery. There was also increased attention from rock-lobster processors interested in processing and marketing champagne crabs and other deep-sea crabs. In April 1999 these issues culminated in the existing endorsement holders, through the Western Australian Fishing Industry Council (WAFIC), asking the Minister for Fisheries to restrict the catch of deep-sea crabs by rock-lobster fishers.
In May 1999, in order to prevent overexploitation, the Department indicated its intention to separately manage the crystal crab fishery and obtained support from the Minster for Fisheries to consult with existing licencees regarding how this fishery should be managed. Existing licencees were subsequently advised of the Department's intentions by letter. This letter in part said: “It is envisaged that, depending on the number of applicants, access will be granted to those who best demonstrate a financial and personal commitment to the ongoing development of their nominated fishery.”A subsequent letter of 18 June 1999 referred to access being granted to “those who best demonstrate a personal and financial commitment to developing a sustainable, market-orientated snow (crystal) crab fishery.”
The Department subsequently warned fishers that investment in the crystal crab fishery was at their own risk. A number of risks have been associated with the initial process. Those with an interest in the fishery may have demonstrated their financial commitment to fishing for crystal crabs by arranging to buy, build or otherwise secure vessels suitable for deep-sea crab fishing. Basing eligibility for access to the fishery on financial commitment created the potential for over-capitalisation in an unproven fishery of unknown capacity. Ultimately seven permit holders were authorized to take crystal crabs on the west coast (the original six plus one who secured an endorsement through a formal objection process).
In December 1999 regulations were gazetted preventing fishers bringing ashore or selling only parts of a deep-sea crab. These regulations were designed to discourage the increasing practice of rock-lobster fishers retaining only the large claws from champagne crabs. While these fishers believed that this practice was conserving the breeding stock, the Department was of the view that there was likely to be a high mortality in crabs that had their claws removed.
In August 2000, to ensure the west coast fishery was not overexploited during this development period, the Minister for Fisheries agreed in principle to the Department negotiating arrangements that would allow only three of the seven west coast endorsement holders to fish full time while the other four could fish for a maximum of three months. The intention of this arrangement was to give all fishers the opportunity to fish for deep-sea crabs should they so wish with the understanding that whether they fished or not, all seven permit holders would have equal access at the end of the developmental phase. The proposal also provided for the fishers to contribute aggregate funds of around $A22 000 a year for research to ascertain the capacity of the fishery. It also incorporated a voluntary management policy that was agreed to by the majority of the seven west coast fishers on the understanding that the Department would subsequently develop a formal interim management plan. These arrangements also provided for the existing zoning of the fishery. The proposal was eventually agreed to by the fishers and formalized by being signed by the majority of fishers in May 2001.
It was recognized that, while documenting the agreed arrangements for operation of the fishery, the signed agreement might be unenforceable in law. During 2001 and 2002 the Department continued to liaise with west-coast fishers and other stakeholders about incorporating these arrangement into a formal interim management plan.
An interim Management Plan for West Coast Deep-Sea Crab Fishery was introduced in January 2003. The plan divides the fishery on the west coast into five zones (Figure 1):
Zone 1 - from the WA/NT border to North
West Cape (south of Exmouth)
Zone 2 - from North West Cape to Carnarvon
Zone 3 - from Carnarvon to Geraldton
Zone 4 - from Geraldton to Fremantle and
Zone 5 - from Fremantle to Cape Leeuwin (north of Albany).
The Interim Management Plan endeavours to place limits on fishing pressure while distributing effort as widely as possible over the grounds to expand the knowledge of the fishery's extent. At the end of the interim management phase it is anticipated that data on the biology, spatial extent of the stock and its robustness to fishing pressure, will enable a rational approach towards exploitation of the resource.
Under the Interim Management Plan there are seven permits. Permits are issued as a full time, ‘Class F’, or part time, ‘Class P’ permit, in the latter case prohibiting the holder from fishing more than three months in the year. The Interim Management Plan restricts operations in the fishery to permit holders, creates five zones in the fishery (Figure 1), restricts the number of permit holders in each zone (a maximum of one Class F and one Class P or two Class P), provides for annual permit fees and controls the type and number of the traps used. Fishers are only permitted to retain deep-sea crabs. Although this part of the Interim Management Plan is currently being contested at this stage there is remarkably little bycatch. There is also provision for the Executive Director to close all, or part, of the fishery for any period during the operation of the Interim Management Plan.
Under the interim plan the masters of authorized boats in the fishery are required to supply the Department with daily records detailing the number of traps used, location fished, catch details (numbers, weight, size and sex) and species caught (including bycatch). Fish processors are also required to provide records related to crab processing to the Department.
Currently the interim plan expires on 31 December 2004. At that point the Department will review the management arrangements and long-term sustainability prospects for the fishery before proposing any replacement legislative instruments for the ongoing management of the fishery.
2.2. The South Coast
Development of the crystal crab fishery on the south coast of the state has taken a different course to the west coast. The south coast has a long history of diversified fishing operations. Rock-lobster licencees generally hold other fishing authorisations and rarely depend on a single fishery for their livelihood. This contrasts with the west coast rock-lobster fishery where many rock-lobster vessels are exclusively used for rock-lobster fishing. With crystal crab resources unproven on the south coast there was initially little interest in creating a separate crystal crab or deep-sea crab fishery. Most of the 26 endorsement holders were satisfied with deep-sea crabs remaining an incidental by-product of rock-lobster fishing operations. This changed in 2002 when one of the west coast licences was reported as being on the market for a price in excess of $A2 million and a number of south coast licences were sold to those interested in exploiting the southern crystal crab stock.
A sudden interest in fishing for crystal crabs on the south coast led managers to become concerned about the considerable latent effort in the fishery. It was apparent from the inquiries received that potential investors had very optimistic views about the earning potential of the fishery; some saw this potential new fishery as comparable to the large North American snow crab fisheries. It was also apparent that some of the existing south coast endorsement holders, realizing that the fishery might only be able to support a few full-time vessels, and being aware of the growing outside interest in the fishery, wanted to take steps to secure “pioneer rights”in the fishery. Together these factors were creating a ‘gold rush’ scenario with a number of operators scrambling to secure licences and gear up for crystal crab fishing. While the current size limits ensure maintenance of breeding stock and biological sustainability it was recognized that without well-considered controls in place there was the potential that the crystal crab fishery would be rapidly depleted to levels that were not economically viable. It also appeared that many of the existing 26 endorsement holders would seek to transfer the endorsement to new licencees who were planning to acquire new vessels to fish for crystal crabs on the south coast and there was a serious risk of substantial overcapitalisation in the fishery.
Without any knowledge of the size or productivity of the crystal crab resource to provide a base for setting management controls, fishing for crystal crab was suspended for one year and since then a second year (until 14 November 2004). This moratorium is to allow research fishing to be undertaken to assess the spatial extent of the resource, which in turn will allow appropriate catch or effort limitations to be determined for the fishery. It also dampened interest in new investment in the fishery and helped reduce the risk of overcapitalization.
Funding has recently (September 2003) been approved for a fishing protocol involving a series of cross-shelf slope transects along each line of longitude using traps at 50 m depth intervals, from 300 to 1500 m. The commercial fishers who assist with the research will be able to fish for a limited time period between the lines of longitude that have been surveyed. This will allow for the relative abundance of crystal crabs to be assessed over the potential commercial fishing ground in this zone and will provide some income to participants in the offshore transect surveys. Three fishers have undertaken to participate in these surveys and they will be required to comply with the same minimum size and trap-type restrictions in place on the west coast. Subsequent management arrangements relating to this fishery will be dependent on the results from the planned experimental fishing.
3. FISHING METHODS
Under the WCDSCIMF plan, fishers are restricted to a maximum of 700 traps in the water at any time. Fishers use moulded plastic rock-lobster traps with a 5 kg flat piece of metal wired to the base of the trap to provide ballast. A side slat is removed to provide one or more escape gaps (56 mm high and 137 mm long) for undersized crabs to escape. The traps are usually set on longlines of approximately 100 traps a line and are baited with fish. The traps are generally left soaking for three to seven days before retrieval and approximately 400–500 traps (four to five longlines) are pulled a day.
Biological restrictions require that all crabs smaller than 120 mm carapace width (approx 700 g), as well as egg bearing females, must be returned to the sea. As most females are below the legal minimum size and the catch in the crystal crab fishery is male-dominated. Fishers are required to submit daily log book catch and effort data for each line of traps fished.
Research objectives have been directed towards obtaining relevant information that will enable decisions to be made on the future of the fishery on the west coast once the interim management period is over and on the south coast once the moratorium period is over. On the west coast this means that research has focused on:
spreading effort and catch in an organized way (by way of the five management zones) to record the longshore extent of the fishery and test its robustness to fishing pressure.
4.2 Distribution and reporting of catch and effort
Commercial crystal crab fishing has focused on the central and southern portion of the grounds. Since 2000 there have been three boats fishing full time and two have operated irregularly on a part-time basis, although this is currently (November 2003) changing, with some previously dormant part-time licences being activated. Most of the fishing has taken place in Zones 2 to 5. There have been a few relatively short trips by permit holders to Zone 1 and although some crystal crabs were landed in that zone in the vicinity of Exmouth (Figure 1), the quantities were non-commercial. Results form exploration in this zone have been inconclusive in providing a solid basis for evaluating the zone's potential, therefore it has not been considered further in the analysis presented here.
Fisheries law in Western Australia requires that all commercial fishers complete monthly catch and effort statistics (CAES) using a 60 × 60 nautical mile grid system to report catch locations. Since 1999 fishers in this fishery have, in addition to CAES data, also been required to complete log books which record accurate global positioning system (GPS) line start and end positions of the longlines, discarded catch (i.e. numbers of undersize, ovigerous, soft and dead animals); bycatch and surface current speed and direction. Catch and effort data presented is a combination of these two data sources.
4.3 Extent of the grounds by zone
To date (November 2003) most commercial fishing for crystal crabs in Western Australia has been within the 500 to 1000 m depth range. In most years, over 90% of the catch has been made in the 500 to 800 m depth range.
A comparison of the area of available fishing ground has been provided in Table 1 for Zones 2 to 5. The area of ground between the 500 and 1000 m depth contours has been estimated in square kilometres by GIS software for each of the management zones on the west coast and for the SCDSCF (Table 1). The percentage of available ground has also been calculated by dividing the total area available in the west coast fishery by the area potentially available in each individual zone on the basis of depth. No attempt has been made to provide the proportion of available fishing ground for Zone 1, or for the SCDSCF, because in both of these zones there is a lack of evidence of the grounds having an extensive presence of crystal crabs. The amount of fishing ground in all of the zones is variable (Table 1). Of the total area of Zones 2–5, Zone 3 contains about half the area of the fishery, i.e. seabed between 500–1000 m.
Estimated areas ('000 km2) covering the 500–1000 m depth zones in Zones 1 to 5 of the WCDSCIMF and SCCF in Western Australia, and the proportion of fishing ground in Zones 2 to 5 of the crystal crab fishery on the west coast
|Area calculations for Zone 1 exclude rises in the 500–1000 m zone offshore from the shelf break.|
|Zone||Area ('000 km2)||% of available ground|
4.4 Total catch, effort and CPUE
Significant landings of crystal crabs started in 1998 on the west coast (Figure 2). Effort has to a large extent tracked catch. The only years with crystal crab landings of any consequence on the south coast were 2001 and 2002 when 0.7 and 10.8 tonnes respectively were landed.
Annual catches of crystal crabs 1997 to 2002 in the WCDSCIMF
Catch per unit effort (CPUE) for the WCDSCIMF is presented in Figure 3. Reliable effort data is only available from 1999 onwards, therefore CPUE data are also limited to this period. Catch rates started low while fishers learned the optimal fishing depths and the best way to deploy gear. Catch rates peaked in 2000 and have since declined.
4.5 Depletion and tagging studies
Attempts at depleting locations by repeatedly setting traps over a relatively small area of the grounds (1.7 km2), have shown that there is rapid localized movement of crabs into depleted areas. It appears that crabs move over the grounds and do not remain within specific home ranges. Preliminary tagging results have shown that there are extensive movements, with some tagged individuals being recorded as moving over 100 km within a year. Growth is likely to be slow, with many tagged crabs having been at large for well in excess of a year without recording a moult.
Annual CPUE for crystal crabs 1999 to 2002 in the WCDSCIMF
Catch rates in 2003 are based on incomplete data.
4.6 Deciding on future catch or effort levels for crystal crab
At this stage, without data, nothing can be stated about possible total allowable catch (TAC) or effort limitations on crystal crab fishing on the south coast. In terms of crystal crab fishing in the WCDSCIMF, existing data will at least provide the basis for establishing future management arrangements. For example, several facts seem clear.
The current large legal minimum size (120 mm CW) makes this a highly male dominated fishery. With size at maturity for both sexes being well below the legal minimum size (size at maturity for females is 89.6 mm and for males 84.1 mm CL [Kim Smith, Murdoch University, Australia, pers. comm.]), there would appear to be little chance of recruitment overfishing of the stock whilst the current minimum size is maintained.
It now appears, in the light of the declining catch rates over time as recorded in Figure 3, that the size and potential productivity of this fishery may be limited. The WCDSCIMF is, as a way of acquiring basic commercial information (e.g. catch rates, product marketability and market prices) and biological information (e.g. fishing localities and depths, size composition/sex ratio data, movement patterns and response of the stock to fishing pressure), necessary for long-term management arrangements.
Landings to date suggest that the fishery is not capable of supporting seven full-time fishers. Markets for the crabs have been shown to be good, but limited. Fishing operations show that there are benefits on the open sea to maintaining zones that separate fishers and thereby avoid gear entanglement.
Setting an appropriate total allowable catch (TAC), or a notional TAC with an associated total allowable effort (TAE), designed to achieve the TAC at the end of the interim management phase will be difficult and an adaptive management regime will be required. The time series of fishing is too short to apply traditional biomass-dynamic models leaving only less sophisticated sustainable-yield models. In addition, crabs tagged in this project appear to have extended intermoult periods and therefore the growth information available will be incomplete.
One preliminary indication of the likely maximum sustainable yield (MSY) for crystal crabs in the WCDSCIMF has been made using Gulland's (1971) adaptation to the Schaefer (Schaefer 1954) model:
MSY = 0.5(M) Bo
M = natural mortality
Bo= biomass of an unexploited population.
This method of estimating maximum sustainable yield has been, and continues to be, used by fisheries managers working in data-limited situations (Sparr, Ursin and Venema 1989), despite the acknowledged shortcomings of the assumptions behind the relationship (Beddington and Cooke 1983, Garcia, Sparre and Csirke 1989).
An initial estimate of Bo for the exploitable portion of the WCDSCIMF biomass has been made by treating four years of catch and effort data as a depletion experiment (DeLury 1947) and by assuming that minimal recruitment and mortality has occurred over these years. For the purpose of this estimate of Bo, catch and effort data prior to 2000 has been excluded. This has been justified on the basis of catches prior to this date being comparatively small compared to subsequent years as well as to the fact that the low CPUE values prior to 2000 were probably due to fishers learning how, and where, to fish for this species. If changes in CPUE since 2000 are accepted as reflecting depletion of the unharvested biomass, then extrapolation of the rate of depletion would suggest that the original fishable biomass might have been of the order of 1200 tonnes (Figure 4).
CPUE for 2000–2003 for Zones 2 to 4, plotted against the cumulative catches reported for those zones
Year 2003 is based on incomplete data.
There is no certainty regarding the natural mortality rate for this species. However, tagging results and temperature measurements taken using archival temperature recorders show this to be a cold-water species that is likely to be slow growing and long lived and therefore likely to have a low rate of natural mortality. Cobb and Caddy (1989) have suggested a general value of M for long-lived crabs and lobsters of around 0.1; other authors working on Chaceon maritae, a species with apparently similar maximum size and growth characteristics to Chaceon bicolor, have used a range of natural mortalities. Melville-Smith (1988) used 0.05 to 0.15 for both sexes, while Le Roux (1997) used 0.05 to 0.15 for males and 0.15–0.25 for females. This fishery targets large, predominantly male animals, and therefore a low value of natural mortality (M=0.05) has been assumed to be most realistic for the maximum sustainable yield (MSY) estimates reported below.
Given the above estimates for Bo and M, then using Gulland's (1971) process for calculating MSY, one may estimate that this fishery might have an MSY of around 30 tonnes a year. It should be noted that estimates of depletion from CPUE over four years (Figure 4) would have led to an overestimate of Bo, because an obvious incorrect assumption has been made that there was no recruitment to the size classes being fished over this period. Further, it is generally accepted (Garcia, Sparre and Csirke 1989) that this method is likely to overestimate MSY. However, countering this possible overestimate of MSY is the fact that fishers tended, at least in the first few years of fishing, to treat crabs of some sizes that were well within the accepted size limit as discards and release them live back onto the grounds. Also, M has been assumed to be negligible over the four-year period of depletion.
It is important to stress that the above estimate of MSY for crystal crabs in the WCDSCIMF should be viewed as no more than a preliminary reference benchmark. The estimate for natural mortality is particularly crucial to the above result. For example, if M = 0.1 and Bo is kept at 1200 tonnes, then using the same equation, MSY would be as high as 60 t; however if M = 0.025, then MSY would be only 15 tonnes.
In the light of the limited information available, this fishery would appear to be capable of withstanding exploitation levels of around 30 tonnes a year and unless different information becomes available before then, a TAC or effort controls to produce landings of this level are likely to be proposed when the interim fishery is reviewed in December 2004.
5. FUTURE MANAGEMENT SCENARIOS FOR THE WEST AND SOUTH COAST FISHERIES
The Department of Fisheries' current proposal for the WCDSCIMF is that once the Interim Management Plan has run to term, all existing permit holders will have equal access to the fishery. Those that are fishing during the interim management period are seen as enjoying the benefit of profits from a previously unfished stock as well as bearing the risks of capital expenditure in a fishery with unknown capacity. Those permit holders that do not participate during the interim management period have none of the potential benefits or risks, yet maintain their stake in the fishery should it turn out to be a profitable venture in the future. From a management point of view this has been beneficial as it has encouraged enough effort to explore the fishery but has prevented the gearing up of additional fishing capacity without justification, yet has allowed fishers with existing rights to retain their stake in the future fishery by not fishing in the early exploratory years.
The allocation of fishing rights for crystal crab in the SCDSCF is yet to be determined. If any new fishing area for crystal crabs were allocated to existing participants in the SCDSCF an increase in fishing effort would be unlikely to threaten the biological sustainability given the existing minimum size. However, there is the potential for catch rates to be reduced to levels that are not economically viable to fish on an annual basis.
A number of lessons have been learnt from the WCDSCIMF and there are problems that will require addressing when the fishery moves to full management. These follow.
Given the indicative landings in the future (around 15–60 tonnes compared to around 200 tonnes a year at present, it will not be feasible for seven fishers to fish full time. Several options therefore exist as to how future sustainable yields might be split up and fished by participants in a management plan. To get to that point, however, it will be necessary to consult with the permit holders as to whether they wish to fish the stock on the basis of small but regular annual landings or larger, but less frequent, episodes of pulse fishing.
We thank the Fisheries Research and Development Corporation for a research grant (2001/055) supporting research on this resource. We acknowledge the assistance of Western Australian Fisheries Department staff Sam Norton who has managed the technical aspects of this project and Adrian Thomson and Eva Lai who have assisted with data extraction. Finally, we thank our colleagues, Ms Alison Fleming and Drs Nick Caputi, Lindsay Joll, Mervi Kangas, Jim Penn and Bruce Phillips for their constructive comments on earlier drafts of this manuscript.
7. LITERATURE CITED
Beddington, J. & J.G. Cooke 1983. The potential yield of fish stocks. FAO Fish. Tech.Pap. 242, FAO, Rome. 56 pp.
Cobb, J. S. & J.F. Caddy 1989. The population biology of decapods. In: Caddy, J. F. (Ed). Marine Invertebrate Fisheries: their assessment and management. John Wiley and Sons. 752 pp.
DeLury, D.B. 1947. On the estimation of biological populations. Biometrics 3: 145–167.
Garcia, S., P. Sparre & J. Csirke 1989. Estimating surplus production and maximum sustainable yield from biomass data when catch and effort time series are not available. Fisheries Research. 8: 113–23.
Gulland, J. 1971. The fish resources of the ocean. West Byfleet, Surrey. Fishing News (Books) Ltd., London, 255 pp.
Hastie, L.C. 1995. Deep-water Geryonid crabs: a continental slope resource. Oceanography and Marine Biology: an Annual Review. 33: 561–584.
Jones, D.S. and G.J. Morgan 1994. A field guide to crustaceans of Australian waters. Reed New Holland, Sydney, Australia, 242 pp.
Kurland, J. 2002.Fisheries of the Caribbean, Gulf of Mexico, and South Atlantic; Comprehensive Sustainable Fishery Act Ammendment to the Fishery Management Plans of the U.S. Caribbean.Federal Register 67 (17): 3679–3680.
Le Roux, L. 1997. Stock assessment and population dynamics of the deep-sea red crab Chaceon maritae (Brachyura, Geryonidae) off the Namibian coast. Unpublished M.Sc. thesis, University of Iceland, Reykjavík, Iceland, 88 pp.
Manning, R.B. & L.B. Holthuis 1989. Two new genera and nine new species of Geryonidcrabs (Crustacea, Decapoda, Geryonidae). Proc. Biol. Soc. Wash. 102 (1): 50–77.
Melville-Smith, R. 1988. The commercial fishery for and population dynamics of red crab Geryon maritae off South West Africa, 1976–1986. S. Afr. J. mar. Sci. 6: 79–95.
Schaefer, M.B.1954. Some aspects of the dynamics of populations important to the management of the commercial marine fisheries.Bull.Inter-Am.trop.Tuna Commn. 1:27–56.
Sparre, P., E. Ursin & S.C. Venema 1989. Introduction to tropical fish stock assessment. Part 1 - Manual. FAO Fish. Tech. Pap. 306/1, 2. FAO, Rome.
A.M. Orlov1 and I.N. Moukhametov2
1 Russian Federal Research Institute of Fisheries & Oceanography (VNIRO),
17, V. Krasnoselskaya, Moscow, 107140, Russia
2 Sakhalin Research Institute of Fisheries & Oceanography (SakhNIRO),
196, Komsomolskaya, Yuzhno-Sakhalinsk, 693016, Russia
Pacific black (Greenland) halibut (Reinhardtius hippoglossoides matsuurae), Kamchatka flounder (Atheresthes evermanni), and Pacific halibut (Hippoglossus stenolepis) are important fishery species in the North Pacific Ocean (Fadeev 1984, Kramer et al. 1995) that consume commercially important species, e.g. walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), saffron cod (Eleginus gracilis), Pacific herring (Clupea pallasii), Japanese sardine (Sardinops melanostictus), capelin (Mallotus villosus), Pacific sand lance (Ammodytes hexapterus), Atka mackerel (Pleurogrammus monopterygius), sandfish (Trichodon trichodon), arrowtooth flounder (Atheresthes stomias), yellowfin sole (Limanda aspera), sculpins (Cottidae), salmons (Oncorhynchus spp.), eelpouts (Lycodes spp.), snailfishes (Liparis spp.) and invertebrates (Fadeev 1984, Best and St-Pierre, 1986, Brodeur and Livingston, 1988, Livingston et al. 1993, Yang 1996, Yang and Nelson 2000, St-Pierre and Trumble 2000). They play an important trophic role in ecosystems of the North Pacific basin though the ecology of these species in the western Bering Sea and in Pacific waters off the northern Kuril Islands and southeastern Kamchatka is poorly known.
The feeding habits of halibut in the western Bering Sea have been investigated by Vernidub and Panin (1937), Vernidub (1936, 1938), Novikov (1974) and Shuntov (1966). Recently published papers on feeding and ecology of four halibut species in the western Bering Sea deal mostly with food rations and seasonal changes of feeding intensity (Napazakov and Chuchukalo 2001) or the diet of Pacific halibut (Chikilev and Palm 2000). Other publications have dealt with the feeding habits of the species in the Kuril-Kamchatka area (Novikov 1974, Orlov 2000). However, descriptions of diet in these papers were based on the frequency of occurrence of dietary components in stomachs. A recent paper by Moukhametov (2002) mostly concerned food rations of Pacific halibut. No studies have been conducted recently of the feeding of Greenland halibut, Kamchatka flounder, and Pacific halibut based on quantitative data on stomach contents in the northwestern Pacific. This paper describes diets depending on size, sex, depth of capture and area, of three halibut species inhabiting the western Bering Sea (WBS) and Pacific waters off the northern Kuril Islands and southeastern Kamchatka (NK).
2. MATERIAL AND METHODS
The stomach contents of Pacific black halibut, Kamchatka flounder and Pacific halibut were sampled aboard the Japanese trawlers Kayo Maru No. 28 and Tomi Maru No. 82 during the summer and autumn of 1997. The study area in the western Bering Sea (WBS) was between 168°E and 178°Eand off the northern Kuril Islands and southeastern Kamchatka (NK) between 47°55' N and 51°40' N (Figure 1). The trawl had a soft ground rope; vertical and horizontal openings were about 5 and 25 m respectively. Fishing was carried out around the clock. Stomach contents were sorted, identified to the lowest possible taxonomic level and weighed to the nearest 0.1 g. Prey groups were described in terms of percent total stomach content weight (%W) and frequency of occurrence (%FO). The frequency of occurrence was calculated as the number of stomachs that contained that prey group divided by the number of stomachs that contained food. Fishes showing signs of regurgitation, flaccid or water-filled stomachs or net-feeding were excluded from the analysis. Fork lengths (FL) were measured throughout.
Study area showing bottom trawl stations (hollow asterisks) where stomachs of Greenland halibut, Kamchatka flounder, and Pacific halibut were sampled
A -northern Kuril Islands and southeastern Kamchatka, B -western Bering Sea (lines and numbers show isobaths in metres)
The number of stomachs used in the analysis was: Greenland halibut 589/411 and 203/93 in the WBS and NK, respectively; Kamchatka flounder 446/184 and 1443/300 in the WBS and NK, respectively; Pacific halibut 262/206 and 386/270 in the WBS and NK.
3. RESULTS AND DISCUSSION
3.1 General description of diets
The diet of all three species consisted of a wide spectrum of items (Table 1). Total number of identified organisms in stomach contents of Greenland halibut was ≥ 29, for Kamchatka flounder, ≥ 31 and of Pacific halibut, ≥ 45. The diet of Greenland halibut in the WBS consisted mostly of fish offal (44.4%W), fishes (42.5%W) and cephalopods (13.1%W). Walleye pollock was the major fish species consumed (30.8%W) followed by Pacific herring (8.9%W). Red squid (Berryteuthis magister) (11.2%W) was most common cephalopod prey. In the NK Greenland halibut consumed mainly cephalopods (73.6%W), small crustaceans (10.6%W), shrimps (8.5%W) and fishes (7.3%W). Red squid (69.4%W) was most common prey among cephalopods but the northern smoothtongue (Leuroglossus schmidti) was the most important fish prey (3.3%W). Differences in diet composition between the areas may be explained by the larger size of WBS fish (69.30 cm vs. 58.62 cm) and regional faunistic distinctions.
During the period 1930–1960s walleye pollock composed the bulk of Pacific black halibut diet in the western Bering Sea (Vernidub and Panin 1937, Gordeeva 1954, Novikov 1974). There was no fishery offal in the diet because the Russian walleye pollock fishery there had not developed yet (Shuntov et al. 1993). Red squid was also the most important dietary component of this predator in the NK area (Novikov 1974, Orlov 2000).
The diet of Kamchatka flounder in the WBS consisted mostly of fish offal (53.4%W), fishes (33.3%W) -mainly walleye pollock (15.5%W) and Pacific herring (10.4%W) and cephalopods (12.7%W) mainly red squid (11.9%W). In the NK this species eat mainly shrimps (53.7%W), various fishes (26.3%W), and cephalopods (18.6%W). Walleye pollock (5.1%W) was the most important fish in the diet of Kamchatka flounder off the northern Kuril Islands and SE Kamchatka. Mesopelagic fishes ranked second (approximately 2.4%W) followed by spectacled sculpin (Triglopsscepticus) (2.2%W). Differences in diet composition between the areas may also result from WBS Kamchatka flounders being considerably larger than NK fishes (54.83 and 49.37 cm, respectively).
Stomach contents of Greenland halibut, Kamchatka flounder and Pacific halibut expressed as percent of frequency of occurrence (%FO) and weight (%W) sampled in the western Bering Sea (WBS) and Pacific waters off the northern Kuril Islands and southeastern Kamchatka (NK), summer-autumn 1997
|Greenland halibut||Kamchatka flounder||Pacific halibut|
|% FO||% W||% FO||% W||% FO||% W||% FO||% W||% FO||% W||% FO||% W|
|Mysidacea gen sp.||0.5||< 0.1||-||-||0.5||0.1||1.0||0.6||-||-||-|
|Gnathophausia gigas||0.2||< 0.1||-||-||-||-||-||-||-||-||-||-|
|Euphausiidae gen sp.||-||-||15.1||1.4||-||-||3.0||0.3||-||-||-||-|
|Isopoda gen. sp.||-||-||-||-||-||-||-||-||-||-||3.7||0.3|
|Amphipoda gen. sp.||-||-||2.2||< 0.1||-||-||0.7||< 0.1||1.0||<0.1||0.7||<0.1|
|Ampelisca sp.||-||-||2.2||< 0.1||-||-||-||-||-||-||-||-|
|Pandalus goniurus||1.2||< 0.1||-||-||1.6||0.1||-||-||1.9||0.1||0.4||<0.1|
|P. hypsinotus||0.2||< 0.1||-||-||1.1||< 0.1||-||-||-||-||-||-|
|Pandalopsis dispar||0.2||< 0.1||-||-||-||-||-||-||-||-||-||-|
|Sclerocrangon sp.||-||-||-||-||-||-||0.7||< 0,1||-||-||0.4||<0.1|
|Pagurus sp.||-||-||-||-||-||-||0.3||< 0,1||8.7||1.2||27.0||5.8|
|Majidae gen. sp.||-||-||-||-||-||-||-||-||0.9||0.1||-||-|
|Decapoda gen. sp.||-||-||-||-||-||-||-||-||-||-||0.4||<0.1|
|Buccinidae gen. sp.||0.2||< 0.1||-||-||0.5||< 0.1||-||-||3.4||0.5||0.7||<0.1|
|Gonatopsis borealis||-||-||-||-||-||-||0.3||< 0,1||-||-||-||-|
|Teuthidae gen. sp.||1.2||< 0.1||-||-||0.5||< 0.1||-||-||-||-||-||-|
|Octopoda gen sp.||0.7||1.9||1.1||6.0||1.1||0.8||1.0||3.3||-||-||3.0||0.5|
|Ophiuroidea gen. sp.||-||-||-||-||-||-||-||-||0.5||<0.1||0.4||<0.1|
|Leuroglossus schmidti||0.2||< 0.1||6.5||1.7||-||-||0.3||0.1||-||-||-||-|
|Myctophidae gen sp.||3.2||0.1||3.2||0.2||-||-||3.0||2.7||-||-||-||-|
|Stenobrachius leucopsarus||0.5||< 0.1||-||-||0.5||0.1||0.3||< 0,1||-||-||-||-|
|Salmonidae gen. sp.||-||-||-||-||-||-||-||-||-||-||0.4||2.0|
|Lycodes palearis||0.2||< 0.1||-||-||1.1||1.1||-||-||0.5||0.2||-||-|
|Lycodes sp.||0.5||< 0.1||-||-||-||-||0.3||0.6||-||-||-||-|
|Zoarcidae gen. sp.||-||-||-||-||-||-||0.3||3.1||-||-||-||-|
|Artediellus sp.||-||-||-||-||-||-||0.3||< 0,1||-||-||0.4||<0.1|
|Icelus sp.||-||-||-||-||-||-||0.3||< 0.1||-||-||-||-|
|Cottidae gen. sp.||-||-||-||-||-||-||0.7||2.0||-||-||0.4||0.1|
|Dasycottus setiger||0.2||< 0.1||-||-||-||-||-||-||-||-||-||-|
|Careproctus furcellus||0.2||< 0.1||-||-||-||-||-||-||-||-||-||-|
|Liparidae gen. sp.||0.2||< 0.1||1.1||0.1||-||-||0.7||3.2||-||-||-||-|
|Fish eggs||-||-||-||-||-||-||0.3||< 0,1||-||-||-||-|
|Unidentified organic material||1.2||< 0.1||-||-||5.4||0.2||-||-||-||-||-||-|
|Number of stomachs analyzed||589||203||446||1443||262||386|
|Stomachs with food||411||93||184||300||206||270|
|Length range, cm||43–102||28–91||37–84||23–78||47–154||35–134|
|Mean length ± SE||69.30 ± 0.43||58.62 ± 0.99||54.83 ± 0.37||49.37 ± 0.25||73.92+0.76||61.40+1.00|
|Weight range, g||730–14200||140–7700||450–6700||100–6600||1.05–56.00||0.33–33.00|
|Mean weight ± SE||3537.0 ± 86.2||2385.2 ± 115.1||1828.0 ± 48.5||1452.7 ± 25.4||5.250+0.271||4.001+0.253|
In the 1930–1960s walleye pollock was the most important dietary component of Kamchatka flounder in the western Bering Sea (Vernidub 1938, Gordeeva 1954, Novikov 1974). No fishery offal was detected in stomach contents during previous studies for the same reason as for Greenland halibut. According to Novikov (1974) and Orlov (2000) the most important dietary components of Kamchatka flounder in the NK area were also shrimps, fish and cephalopods.
The diet of Pacific halibut consisted of awide range of prey. The total number of identified organisms (excluding fishery offal) in halibut stomachs was ≥25 in the WBS and 32 in the NK. The diet of Pacific halibut in the WBS area comprised mostly fishes (35.1%W), fish offal (31.3%W) and cephalopods (26.6%W). Walleye pollock represented the major fish consumed (18.7%W) followed by Pacific herring (12.9%W). The most common mollusks were red squid (13.6%W) and octopi (13.0%W).
In the NK, Pacific halibut consumed mainly fishes (38.9%W) and cephalopods (36.8%W). Fish offal in the diet of halibut was less import than in the first area (9.3%W). As was similar to the WBS area, walleye pollock (21.8%W) was most important prey among fishes and octopi were the most significant cephalopod prey (23.5%W). Some differences in Pacific halibut diet composition between the areas may also be explained by the considerably larger size of WBS fish (73.92 cm vs. 61.40 cm).
In the 1930–1960s (Vernidub 1936, Gordeeva 1954, Novikov 1974) walleye pollock composed the bulk of Pacific halibut diet in the western Bering Sea though Vernidub (1936) found crustaceans to be the most frequent prey items. These authors found the occurrence of cephalopods in halibut diet to be insignificant. According to Novikov (1974) the main food items of Pacific halibut in the NK area were fish (27.1%FO), Tanner crabs (16.7%FO) and cephalopods (10.4%FO). Recent studies (Orlov 2000) showed that the most important dietary components were fish following by cephalopods and crustaceans. Most significant prey items among cephalopods were octopi and red squid. Walleye pollock was the most important fish prey species.
3.2 Feeding habits versus size
Diet composition of all three species changed with size (Figure 2). In the WBS, increase in Greenland halibut size was accompanied by an increase of fishes and fish offal and decrease of cephalopods in the diet. In the NK, larger Greenland halibut (size groups 46–80 cm) ate more cephalopods (86.6%W). The role of cephalopods in the WBS fish's diet of the same size group was considerably lower (only 28.0%W). Small NK individuals (FL<45 cm) ate mostly euphausiids, shrimps and fish. The role of fish offal in the diet of WBS Kamchatka flounder increased with size. Fish prey were important for all size groups. Cephalopods played an essential role (34.6%W) in the diet of specimens 41–50 cm long. In the NK an increase in Kamchatka flounder size was accompanied by a decrease in consumption of shrimps and increase of cephalopods and fish.
Considerable changes in the Pacific halibut diet occurred with increasing fish size for both study areas. In the WBS, increase in size of Pacific halibut was accompanied by increased consumption of fishes and decrease of fish offal. The proportion of cephalopods was approximately equal in the diets of various length categories though the importance of red squid decreased and octopi increased with increase of halibut length.
In the NK area variations in length of Pacific halibut were significant. Small fish (<50 cm) ate mostly hermit crabs, small crustaceans (isopods and amphipods), Tanner crabs, shrimps and fish. Hermit crabs in halibut diet decreased with increase in predator length and became insignificant when halibut reached 60 cm in length. Tanner crabs were important in halibut diet in all length categories though their average proportion comprised only 2%W of stomach contents of fish larger than 70 cm. The role of cephalopods, fishes and fishery offal rose with an increase in predator size. The largest fish almost exclusively ate octopi.
Shuntov (1966) documented differences in the occurrence of squids, fishes and invertebrates in stomachs of various size groups for Greenland halibut and Kamchatka flounder. Size-dependent diet differences of Pacific halibut in the western Bering Sea were first described by Napazakov and Chuchukalo (2001) and Novikov (1964) showed differences in the occurrence in stomachs of fishes and invertebrates for three halibut size groups: 30–60, 60–90 and >90 cm. Orlov (1977) reported on distinctions in diet depending on fish size for all three halibut species in the Pacific waters off the northern Kuril Islands and southeastern Kamchatka.
3.3 Feeding habits as a function of capture depth
Differences in fish diet by depth were detected (Figure 3): the stomach contents of WBS Greenland halibut at shallower depths consisted mostly of fish offal and fish, mainly of walleye pollock. With increasing depth fish offal decreased from 63.1%W at 201–300 m to 33.1%W at 401–500 m while cephalopods increased from 5.0%W to 26.3%W. In the NK area at shallower depths Greenland halibut ate mostly euphausiids and shrimps and at greater depths, mainly red squid and predominantly mesopelagic fish.
Kamchatka flounders eat mostly fish offal at shallower depths (201–400 m) and mainly Pacific herring, walleye pollock and other fish at greater depths. In the NK this species fed predominantly on shrimp and fish at shallower depths (101–300 m); at greater deeper depths they ate mainly red squid and fish.
The stomach contents of WBS Pacific halibuts at shallower depths consisted mostly of fish offal and fish -mainly walleye pollock. Fish offal decreased from 63.8%W at 251–300 m to 17.5%W at 401–450 m and cephalopods increased from 9.1%W to 47.5%W. The proportion of fishes in the diet of Pacific halibut increased from 23.5%W at 251–300 m to 56.8%W at 351–400 m and subsequently declined to 9.4%W at greatest depths. In the NK increasing depths were accompanied by decreasing fractions of fish in the diet of Pacific halibut while that of cephalopods increased. Fish offal comprised 9.5–11.1%W of stomach contents at 151–300 m. Hermit crabs were important within all depth ranges (3.7–13.6%W).
Variation in the main food items of Greenlan halibut (left column), Kamchata flounder (center column), and Pacific halibut (right column), by predator size A - western Bering, B - northen Kuril Island (sample size is shown in parentheses)
3.4 Feeding habits vs. sex
Differences between male and female diets were detected for all three halibut species (Figure 4). Female Greenland halibut in the WBS ate more fish offal (47.5%W) and walleye pollock (35.5%W). Males fed mostly on fish offal (35.2%W), red squid (25.3%W) and Pacific herring (17.6%W). In the NK area Greenland halibut females consumed more fish and red squid while males ate larger amounts of shrimps -12.3%W vs. 3.5%W for males and females, respectively.
Female Kamchatka flounders in the WBS fed mostly on fishery offal (64.4%W) while males consumed more fishes (50.6%W), especially Pacific herring -25.1%W and red squid (22.2%W). In the NK, females ate more shrimps (59.8%W) and large fish (27.4%W) while males fed mostly on red squid (26.6%W) and small fish species (25.0%W). Nevertheless, the most abundant prey items of male diets by weight were shrimps -45.8%.
Female Pacific halibut in the WBS ate more fish offal (36.9%W), fish (31.2%W) and cephalopods (27.1%W) while in male fish diets fish represented 38.0%W, fishery offal -27.2%W, and cephalopods -26.2%W. Males consumed no less than nine species while female stomachs contained only four species; the most important components for both sexes were walleye pollock (18.2%W and 19.5%W for males and females, respectively) and Pacific herring (15.2%W and 9.8%W for males and females, respectively). Differences in the proportions of red squid and octopi in male and female diets were also observed -Pacific halibut males eat more red squid then octopi (16.1%W vs. 10.1%W respectively). Females preferred octopi (16.8%W vs. 10.2%W, respectively). In the NK area, Pacific halibut females consumed more cephalopods (42.5%W), fish (31.2%W) and fishery offal (10.8%W) while males ate considerably more fish (45.1%W); cephalopods ranked second in male halibut diets (33.3%W). As for the WBS region, fish found in male halibut stomachs were larger; the main prey of both sexes was walleye pollock. No major differences were detected between male and female consumption of cephalopods, as in the WBS area.
Differences in the diet between males and females are mostly related to size; average size of males in both areas were shorter than females: 63.5 vs. 74.1 cm and 53.8 vs. 55.7 cm for Greenland halibut in WBS and NK, respectively; 52.3 vs. 56.6 cm and 40.9 vs. 42.9 cm for Kamchatka flounder, respectively; and 72.5 vs. 75.9 cm and 59.9 vs. 62.3 cm for Pacific halibut, respectively.
3.5 Feeding habits vs. area
Regional differences were observed in the diets of all three halibut species in the two study areas (Table 2). Fishes (61.4%W) and cephalopods (37.2%W) were more important in the diet of Greenland halibut caught in the western part of WBS while fish offal (59.9%W) and fishes (35.6%) were the most significant dietary components in the eastern part. The diet of Greenland halibut in the NK area changed with increasing importance of small crustaceans and shrimps in the diet and decreasing importance of cephalopods and fishes from south to north.
The diet of Kamchatka flounders in the western part of WBS consisted mostly of fish (71.2%W) and cephalopods (22.7%W); in the eastern part they ate mainly fish offal (73.6%); fish prey ranked second. In the NK area, the importance of cephalopods decreased from south to north while the reverse was true for shrimps. Thus, in the southern part of the study area cephalopods were the most important dietary component (53.7%W), in the mid-part they were second in importance (22.4%W) but in the north, cephalopods were negligible (1.6%W). Shrimp presence increased from 8.6%W in the south to 82.9%W in the north.
Variations in the food items of Greenland halibut (left column), Kamchatkaflounder (center column), and Pacific halibut (right column), by depth range A - western Bering Sea, B - northen Kuril Islands (sample size is shown in parentheses)
Variations in the main food items of Greenland halibut (A), Kamchatka flounder (B) and Pacific halibut (C), by sex
WBS -western Bering Sea, NK -northern Kuril Islands; -males ♂, -females ♀ (sample size is shown in parentheses)
Fishes (43.9%W) and cephalopods (42.9%W) were more important in the diet of Pacific halibut caught in the western part of WBS while fish offal (67.9%W) and fishes (23.5% W) were the most significant dietary components in the eastern part, where the share of cephalopods in the diet was only 5.3%W. Considerable differences occurred in consumption of crabs in the western and eastern parts of WBS area (8.2%W vs. 1.4%W). The consumption of fish and cephalopod by Pacific halibut in the NK area changed from south to north (fish increased while cephalopods decreased). In the southern NK area, fishes represented 12.6% of the diet, third after cephalopods (46.2%W) and fish offal (19.1%W). In the central area fishes ranked second in importance (37.2%W). In the northern part their significance increased to 41.0%W and they were the most important prey item of Pacific halibut. The importance of cephalopods decreased northward reaching 35.9%W in the northernmost area. Differences in consumption of hermit crabs and fishery offal were also found.
Differences in diet between various parts of NK study areas may be explained by differences in predator size (62.2, 55.2 and 39.4 cm for Greenland halibut; 51.9, 40.3, and 35.9 cm for Kamchatka flounder; and 52.7, 54.9, and 65.2 cm for Pacific halibut in the southern, middle and northern parts respectively) and probably by faunal differences.
Regional differences of halibut diets in the western Bering Sea were first considered by Gordeeva (1954), when the walleye pollock fishery in this area was not developed. Napazakov and Chuchukalo (2001) considered regional differences of halibuts in the western Bering Sea, however, they combined their data from areas east and west of 174°E, which we consider separately. Moreover, they did not report fish offal among dietary components of halibuts. It is uncertain whether they excluded fish offal from analysis or included it in the category of unidentified fishes. The importance of offal in the diet of all three species in the eastern part of the western Bering Sea (this study) is probably related to the walleye pollock fishery in this area.
Variations in the main food items of Greenland halibut, by area of samples
WBS -western Bering Sea, NK -northern
e - 174°E–178°W,
s - 47°50'–49°30' N,
m - 49°35'–50°40' N,
n - 50°50'–51°30' N
|Food items||Greenland halibut||Kamchatka flounder||Pacific halibut|
We thank Dr. Sergei Moiseev (Russian Federal Research Institute of Fisheries and Oceanography, Moscow, Russia) and Dr. Yuri Poltev (Sakhalin Research Institute of Fisheries and Oceanography, Yuzhno-Sakhalinsk, Russia) who assisted us in collecting stomachs during research cruises aboard the Japanese trawlers Kayo Maru No. 28 and the Tomi Maru No. 82 in the summer-autumn of 1997.
5. LITERATURE CITED
Best, E.A. & G. St.-Pierre 1986. Pacific halibut as predator and prey. IPHC Technical Report. 21:1–27.
Brodeur, R.D. & P.A. Livingston. 1988. Food habits and diet overlap of various Eastern Bering Sea fishes. U.S. Department of Commerce, NOAA Technical Memorandum NMFS F/NWC. 127:1–76.
Chikilev, V.G. & S.A. Palm. 2000. Commercial importance of Pacific halibut of the northwestern Bering Sea shelf. Biological resources of the Russian coastal Arctic. Materials of Symposium. Belomorsk, April 2001. Moscow: VNIRO, p. 192–198 (In Russian).
Fadeev, N.S. 1986. Halibuts and flounders. In Vinogradov, M.E. et al. (Eds). Biological resources of the Pacific Ocean. Moscow: Nauka, P. 341–365 (In Russian).
Gordeeva, K.T. 1954. Feeding of halibuts in the Bering Sea. Izvestiya TINRO. 39:111–134 (In Russian).
Kramer, D.E., W.H. Barss, B.C.Paust et al. 1995. Guide to northeast Pacific flatfishes. Marine Advisory Bulletin. 47:1–104.
Livingston, P.A., A. Ward, G.M. Lang & M-S. Yang 1993. Groundfish food habits and predation on commercially important prey species in the Eastern Bering Sea from 1987 to 1989. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-AFSC. 11:1–192.
Moukhametov, I.N. 2002. Feeding habits and food rations of halibut, inhabiting Pacific waters of the North Kurils. Water life biology, resources status and condition of inhabitation in Sakhalin-Kuril region and adjoining water areas. Trudy SakhNIRO. 4:149–162 (In Russian).
Napazakov, V.V. & V.I. Chuchukalo 2001. Feeding and some features of ecology of four flatfish of the western Bering Sea in summer-autumn season. Voprosy Rybolovstva. 2(6):319–337 (In Russian).
Novikov, N.P. 1964. Basic elements of the biology of the Pacific halibut (Hippoglossus hippoglossus stenolepis Schmidt) in the Bering Sea. Izvestiya TINRO. 51:167–207 (In Russian).
Novikov, N.P. 1974. Commercial fishes of the North Pacific Ocean continental slope. Moscow: Pishchevaya Promyshlennost, 308 pp. (In Russian).
Orlov, A.M. 1997. Ecological characteristics of the feeding of some Pacific predatory fish of South-East Kamchatka and northern Kuril Islands. Russian Journal of Aquatic Ecology. 6(1–2):59–74.
Orlov, A.M. 2000. Trophic relationships of predatory fishes in the Pacific waters off the northern Kuril Islands and southeastern Kamchatka. Gidrobiologicheskii Zhurnal. 5:19–33 (In Russian).
Shuntov, V.P. 1966. Some peculiarities of vertical distribution of Greenland halibut and arrow-tooth flounders in the North Pacific Ocean. Voprosy Ikhtiologii. 6(1):32–41 (In Russian).
Shuntov, V.P., A.F. Volkov, O.S. Temnykh & E.P. Dulepova. 1993. Walleye pollock in the Far East seas ecosystems. Vladivostok: TINRO, 426 pp (In Russian).
St-Pierre, G. & R.J. Trumble 2000. Diet of juvenile Pacific halibut, 1957–1961. International Pacific Halibut Commission Technical Report. 43:1–16.
Vernidub, M.F. 1936. Some data concerning the Pacific form of Hippoglossus hippoglossus. Trudy Leningradskogo Obshestva Estestvoispitatelei. 65(2):143–184 (In Russian).
Vernidub, M.F. 1938. Arrow-tooth flounders of the Far East seas. Trudy Petergofskogo Biologicheskogo Instituta. 16:182–199 (In Russian).
Vernidub, M.F. & K.I. Panin 1937. Some data on systematic position and biology of Pacific representative of Reinhardtius Gill. Uchyonyie Zapiski Leningradskogo Gosudarstvennogo Universiteta. 3(15) : 250–272 (In Russian).
Yang, M-S. 1996. Diets of the important groundfishes in the Aleutian Islands in Summer 1991. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-AFSC. 60:1–105.
Yang, M-S. & M.W. Nelson 2000. Food habits of the commercially important groundfishes in the Gulf of Alaska in 1990, 1993 and 1996. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-AFSC. 112:1–174.