Pelagic fishery for Sebastes mentella in the Irminger Sea

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1 3.2.6.d Pelagic fishery for Sebastes mentella in the Irminger Sea The stock structure of deep-sea redfish S. mentella in Sub-area XII, Division Va and Sub-area XIV and NAFO Div. 1F remains generally uncertain. There is a difference in the depth distribution of the two pelagic redfish types, namely the oceanic S. mentella, mainly above 500 meters, and the pelagic deep-sea S. mentella, mainly below. State of stock/exploitation: The stock appears to be at or below 50% of the biomass in the early the 1980s, which was estimated to be around 3 million tons, although stock indicators are uncertain. The 1999 survey indicated a continued reduction in the stock abundance and biomass above 500 m, with a major portion of the stock found in the NAFO Div. 1F for the first time. The survey estimated an additional biomass index of around t below 500 m. A negative trend is seen in the CPUE shallower than 500 m. A recruitment pulse to the fishable stock was observed in 1999, both below and above 500 m. The recent catches might be above the 5 % exploitation rate considered sustainable. Management objectives: There is no explicit management objective for this stock. However, for any management objective to meet precautionary criteria, U (index for trawl-acoustic surveys) should be greater than the proposed U pa. Advice on management: ICES again advises a reduction of catches in 2002 to below t (including NAFO Div. 1F). In addition, ICES advises that management measures are required to ensure that the possible stock components in the pelagic fishery in the Irminger Sea will not be overexploited. These measures are necessary because of the large decline in biomasses and CPUE during the 1990s, the low productivity of the stock, and the need to prevent further declines in the stock. Comparison with previous assessment and advice: The most recent survey information is derived from The next international hydroacoustic survey is planned for June/July Special requests: NEAFC has requested ICES as follows: There are uncertainties about the stock structure of pelagic redfish in the Irminger Sea. Genetic studies suggest that Sebastes mentella in this area, like many other species of Sebastes, has a complex stock structure. However, the number of separable units, and the degree of exchange among them, both genetically and in terms of their population dynamics, is largely unknown. Moreover, their relative productivities are also unknown, but may not be equal. In light of these sources of uncertainty and the risk of local depletions of populations, which would recover very slowly, if at all, management should emphasize distributing effort widely, and monitoring local units for evidence of depletion. Associated risks in overexploitation of the different stock components managed under a common TAC cannot be quantified. Since 1998 a) the fisheries in the northeastern area in the first half of the year occurred at depths greater than 500 m and catching larger fish, and b) the fisheries in the southwestern area in the second half of the year occurred mainly at depths shallower than 500 m catching smaller fish. Relevant factors to be considered in management: The advised catch of t is 75% of the average, a period when catches were unsustainable. The estimated biomass in the 1999 acoustic survey was between 10 and 20% of that estimated in the early 1990s. However, the 1999 acoustic survey estimate is considered an underestimate due to significant changes in horizontal and vertical stock distribution patterns. Changes in fishery patterns in recent years forming 2 almost distinct fishing grounds in terms of geographic distribution and trawling depth, and unknown stock structure provide further cause for concern. In 2000, substantial catches were taken for the first time from the pelagic S. mentella aggregations discovered recently in NAFO Div. 1F. There are, as of yet, no indications that the pelagic S. mentella in NAFO Div. 1F are distinct from the stock(s) or components in the adjacent Irminger Sea, so these catches may represent an increase in exploitation of the stock that has supported the fishery in the Irminger Sea. There may be a relationship between the demersal deepsea S. mentella on the continental shelves of the Faroe Islands, Iceland, Greenland and the pelagic S. mentella components in the Irminger Sea and this should be kept in mind in the management of these components. Management action should be taken to prevent a disproportional high exploitation rate of any one component. Since this is a relatively new fishery on a long-lived, slow-growing species, ICES notes that monitoring of the stock is essential in order to keep track of biomass changes as they occur. Similarly, it is important to gather the information needed to evaluate the productivity of the stock. This includes information on ICES Cooperative Research Report No

2 recruitment, nursery areas, stock identification and biomass estimation. Nursery areas for both of the pelagic stock components are likely to be found at the continental slope off East Greenland. The juvenile redfish in these areas should, therefore, be protected and appropriate measures to reduce the by-catches in the shrimp fishery need to be taken. Elaboration and special comment: The pelagic fishery in the Irminger Sea is conducted only on the mature part (approximately 95% mature) of the stock. The fishery started in After decreasing from , landings increased. The decrease was mostly due to a reduction in Russian effort. The increase in the catches from is a direct consequence of increased fishing effort due to new fleets entering the fishery. However, the catches have been significantly lower during the last 4 years; at the same time the fishery has expanded into deeper water and the season has expanded from March to December. New survey information will be available after the June/July 2001 survey has been carried out. Given the technical, seasonal, geographical and depth changes of the fishing activities, the relevance of the estimated reduction in CPUE as indicator of stock abundance remains difficult to assess both above and below 500 m. Data on maturity at length, and at weight and some agereading experiments were available from both the survey and from the fishery. CPUE series are available for some fleets (Figures d.1 2). Source of information: Report of the North-Western Working Group, April/May 2001 (ICES CM 2001/ACFM:20). 136 ICES Cooperative Research Report No. 246

3 Catch data for oceanic and pelagic deep-sea S. mentella combined (Tables d.1-2): Year ICES Advice Predicted catch corresp. to advice Agreed TAC 1987 No assessment No assessment TAC TAC TAC Preference for no major expansion of the fishery TAC TAC TAC No specific advice No specific advice TAC not over recent ( ) levels of t 1999 TAC to be reduced from recent ( ) levels of t TAC set lower than recent ( ) catches of t 2001 TAC less than 75% of catch TAC less than 75% of catch Set by NEAFC. 2 Preliminary. (Weights in '000 t). ACFM Catch Pelagic fishery for Sebastes mentella in the Irminger Sea Landings 200 Landings in 1000 t ICES Cooperative Research Report No

4 Table d.1 fishery. Results of dividing the Icelandic pelagic redfish catch according to the Icelandic samples from the Year Total catch Catch oceanic Catch deep-sea Not classified % oceanic % % % % % % Table d.2 Pelagic S. mentella. Landings (in tonnes) by area as used by the Working Group. Due to the lack of area reportings for some countries, the exact share in Divisions XII and XIV is approximate in latest years. The Table includes catches in NAFO Div. 1F. Year Va Vb VI XII XIV NAFO 1F Total ,783 20,798 60, , , ,643 4,189 64, ,300 54,371 71, ,131 80, , ,948 88,221 91, ,772 81,647 91, ,233 21,551 38, ,039 24, , ,061 17, , , ,249 40,745 65, , ,529 40, , , ,189 39, , , ,039 42, , , , , , , ,822 87, , , ,446 53, , , ,085 48, , , ,172 51,451 10, ,244 1 ) Provisional data 138 ICES Cooperative Research Report No. 246

5 CPUE (t/h) Bulgaria Germany Iceland Norway Spain Biomass <500 m Biomass (1000 t) Year 0 Figure d.1 Trends in CPUE of pelagic S. mentella fishery in the Irminger Sea, shallower than 500m, and estimated acoustic biomass from surveys. 2.5 Jan-Jun; >500 m CPUE (t/h) Germany Iceland Spain Year Figure d.2 Trends in CPUE of pelagic S. mentella fishery in the Irminger Sea, deeper than 500m, and estimated acoustic biomass from surveys. ICES Cooperative Research Report No