The Present Status of Beaked Redfish (S. mentella and S. fasciatus) in NAFO Division 3M and Medium Term Projections Under A Low Commercial Catch/ High Shrimp Fishery By-Catch Regime

Abstract

The present assessment evaluates the status of the Division 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 1989-2001 commercial catch with the 1993-2001 by-catch is the Div. 3M redfish catch at length input of this assessment. The VPA based models used a 1989-2001 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 2001 XSA framework. The consistency of the XSA results was checked with a Retrospective Analysis confined to the assessments of the most recent years, 2001-1999. A Separable/Cohort analysis (Pope and Shepherd, 1982) has also been performed afterwards. Compared with XSA the Cohort/SPA model systematically under estimated both stock biomass and spawning stock biomass over the past thirteen years. Despite an apparent lack of residual patterns, the Separable model has a poorer fit to the commercial catch at age matrix than the Extended Survivor model. A logistic surplus production model (ASPIC) which does not use the equilibrium assumption (Praguer, 1994 and 1995) was also applied using the 1959-2001 catch coupled with the STATLANT standardized CPUE series (1959-1993) and the age 4 plus EU bottom biomass (1988-2001). The ASPIC results, as regards biomass and fishing mortality trends are identical to the ones from the VPA based models though with a faster rate of biomass increase over the final years of 1999-2001. Either VPA’s and ASPIC analysis pointed out that the Div. 3M beaked redfish stock experienced a steep decline from the second half of the 1980s 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 natural mortality. Despite recent fluctuations biomass and female spawning biomass are generally increasing since 1997 but at a slow rates, being still well bellow the levels of the first years of the time series. However the stock reproductive potential has increased through the nineties compensating the SSB decline and sustaining recruitment at the late-1980s and early-1990s level. By-catch mortality continued to act as a buffer on survival of pre-recruits and its impact increases with year-class strength. With the XSA survivors and recruitment randomly resample from the 1999-2001 geometric mean, short- and medium-term projections were made under three fishing mortality options. Keeping fishing mortality at Fstatus quo will allow a moderate increase of SSB but by the beginning of the next decade female spawning biomass will still be far away from the SSB levels higher than 80,000 tons recorded prior to 1991 and associated with strong recruitments. On the contrary, a reduction to 45%-60% of Fstatusquo will anchored in the short term caches to an interval defined by the present level of catches and the adopted 2000-2002 TAC, but will allow a medium term female spawning biomass closer to that 80,000 tons SSB frontier.