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A comparative assessment and medium term projections of redfish (S. mentella and S. fasciatus) in NAFO division 3M

AuthorsÁvila de Melo, A.; Alpoim, R.; Saborido-Rey, Fran
Issue Date2001
PublisherNorthwest Atlantic Fisheries Organization
CitationScientific Council Research (SCR) Document 01/45 (2001)
AbstractThe present assessment evaluates the status of the 3M beaked redfish stock, regarded as a management unit composed of two populations from two very similar species (Sebastes mentella and Sebastes fasciatus). Survey bottom biomass and survey female spawning biomass were calculated based on the abundance at length from Canadian (1979-1985) and EU (1988-2000) bottom trawl surveys, and on the length weight relationships derived from EU survey data. The analytical assessment used a 1989-00 catch at age matrix starting at age 4 and incorporating the 1993-2000 redfish by-catch in the shrimp fishery at age. An Extended Survivor Analysis (Shepherd, 1999), including a 2000-1994 Retrospective Analysis, was first performed and complemented further by a Separable/Cohort analysis (Pope and Shepherd, 1982). Both models gave similar trends of stock biomass, spawning stock biomass and fishing mortality over the past twelve years. However the full weight of the former high catches of adult beaked redfish (greater than 30cm) on the SPA fit of the correspondent fishing mortalities lead to higher 1989-1993 F’s from the Cohort analysis and lower 1989-1998 SSB’s than those from XSA. A logistic surplus production model (ASPIC) which does not use the equilibrium assumption (Praguer, 1994 and 1995) was also applied using the 1959-2000 catch coupled with the STATLANT standardised CPUE series (1959-1993) and the age 4 plus EU bottom biomass (1988-2000). These last results, as regards biomass and fishing mortality trends are identical to the VPA based ones though with a faster rate of biomass increase over the final years of 1998-2000. Either VPA’s and ASPIC analysis pointed out that the 3M beaked redfish stock experienced a steep decline from the second half of the eighties till 1994-1996. Biomass is increasing since then but is still well bellow the level estimated by each model for the beginning of the time series (1989). Till 1996 fishing mortality was kept well above Fmsy, due to a period of extremely high commercial catches from the direct fishery (1989-93) followed by an extremely high level of redfish by-catch in numbers from beginning of the 3M shrimp fishery (1993-94). From 1997 onwards fishing mortality dropped to values well below natural mortality allowing the survival and growth of the remainders from all cohorts, namely from those most abundant ones, and forcing a discrete growth of the biomass and female spawning biomass. Meanwhile, no new pulse of recruitment has occurred since 1990-1989. With the XSA survivors and recruitment randomly resampled from the 1998-00 geometric mean, short and medium term projections, under F and TAC status quo, were made for several probability levels. The underlying assumption of these projections was that no pulse of recruitment would be foreseen in the next coming years. Maintaining in the short term the catches at the TAC level will represent a 50% reduction on Fstatus quo. Under this scenario, and considering a high probability given by the 20% percentile profiles, catches will be anchored to levels between 4,000 tons and 5,000 tons till the end of this decade but female spawning stock biomass should reach in 2010 the vicinity of the 1990 SSB, that generated the last abundant cohort seen in this stock. Until 3M beaked redfish stock returns to a “normal” rhythm on the pulse of recruitment, the future increase of the female stock biomass will continue to be dependent on keeping fishing mortality well below F0.1. At the present magnitude of the exploitable stock biomass, and at least in the short term, this will correspond to an annual catch not going beyond 5,000 tons
Description66 páginas, 19 tablas, 10 figuras.-- Scientific Council Meeting
Publisher version (URL)http://archive.nafo.int/open/sc/2001/scr01-045.pdf
Appears in Collections:(IIM) Artículos
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