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Open Access item An assessment of beaked redfish (S. mentella and S. fasciatus) in NAFO division Div. 3M

Authors:Ávila de Melo, A.
Alpoim, R.
Saborido-Rey, Fran
Issue Date:2003
Publisher:Northwest Atlantic Fisheries Organization
Citation:Scientific Council Research (SCR) Document 03/45 (2003)
Series/Report no.:N4863
Abstract:The present assessment evaluates the status of the Div. 3M beaked redfish stock, regarded as a management unit composed of two populations from two very similar species (Sebastes mentella and Sebastes fasciatus). The sum of the absolute length compositions of the 1989-2002 commercial catch with the 1993-2002 by-catch is the Div. 3M redfish catch at length input of this assessment. The VPA assessment used a 1989-2002 catch at age matrix starting at age 4 and having a plus group at age 19. An Extended Survivor Analysis (Shepherd, 1999) was performed using the previous XSA framework. The consistency of the XSA results was checked with a Retrospective Analysis confined to the assessments of the most recent years, 2002-2000. A logistic surplus production model (ASPIC) which does not use the equilibrium assumption (Praguer, 1994 and 1995) was also applied using the 1959-2002 catch coupled with the STATLANT standardised CPUE series (1959-1993) and the age 4 plus EU bottom biomass (1988-2002). The ASPIC results, as regards biomass and fishing mortality trends are comparable to the ones from the XSA but with biomass declining to a lesser extent and increasing at faster rate from 1998 onwards. Either XSA or ASPIC analysis pointed out that the Div. 3M beaked redfish stock experienced a steep decline from the second half of the eighties till 1996. Fishing mortality was kept well above Fmsy over the first half of the assessment period. From 1995 onwards fishing mortality dropped and since 1997 has been kept well below the assumed natural mortality. Despite recent fluctuations biomass and female spawning biomass are generally increasing since 1997 but at slow rates, being still well bellow the levels of the first years of the time series. The stock reproductive potential has increased through the nineties compensating the SSB decline and sustaining a 1998-2002 geo-mean recruitment at age 4 identical to the former years of 1989-1993. The 1998 year-class at age 4, recruiting in 2002, is well above the 1989-2002 geo-mean recruitment (including both 1989 and 1990 above average year-classes). However by-catch mortality continued to act as a buffer on survival of pre recruits and its impact increases with the appearance of good year-classes such as the 1998 and the promising 2000 year-class. Short (2006) and medium term (20012) projections were made with the XSA survivors and recruitment randomly re-sampled, assuming two productivity scenarios: one including all recruitments (observed productivity) and the other excluding the recruitment peaks (low productivity). A single option of fishing mortality was considered, and corresponding to short term catches within an interval defined by the recent level of total catch of 4 000 tons and the actual TAC of 5 000 tons. Such option is given by 40% Fstatuquo. Taking into account the trajectories of the last Mterm projections, further increase of the stock and spawning biomass will continue so far to be dependent on keeping fishing mortality at a low level, below both the assumed natural mortality and 0.1 F . At the present stock size this should correspond to a level of catch not higher than 5 000 tons until the end of the present decade, regardless the recruitment regime that will prevail on the near future
Description:72 páginas, 19 tablas, 17 figuras.-- Scientific Council Meeting
Publisher version (URL):http://archive.nafo.int/open/sc/2003/scr03-045.pdf
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