A Revised Assessment of Beaked Redfish (S. mentella and S. fasciatus) in NAFO Division 3M Using the Original EU Survey Indices Converted to the New RV Vizconde de Eza Units

Abstract

The 3M beaked redfish stock is regarded as a management unit composed of two populations from two very similar species (Sebastes mentella and Sebastes fasciatus). In June 2003 a new Spanish research vessel, the RV Vizconde de Eza (VE) replaced the RV Cornide de Saavedra (CS) that had carried out so far the EU survey series with the exception of the years of 1989 and 1990. In order to preserve the full use of the 1988-2002 survey indices available for beaked redfish, the original time series were converted to the new RV units. An Extended Survivor Analysis (Shepherd, 1999) was performed using the previous XSA framework and the revised EU survey abundance’s at age as the tuning input file. In order to evaluate the effect of the conversion of the original 1989-02 survey abundance at age matrix to the new RV units the original 2003 XSA results are compared with the results of the present analysis. The update of the survey abundance at age tuning matrix kept the general trends of either biomasses and fishing mortality, but re-scaled each stock parameter to a new dimension that has proven to have a much better fit to both survey and commercial data. Very high fishing mortalities until 1996 forced a rapid and steep decline of abundance, biomass and female spawning biomass of the Div. 3M beaked redfish stock. From 1997 onwards, low fishing mortalities allowed a slow but continuous growth of both 4+ Biomass and female SSB. Abundance was kept stable at a low level from 1996 to 2001, increasing afterwards with the recruitment of the above average 1998-2000 year-classes to the 4+ stock. Medium term trajectories of female spawning stock biomass under a gradient of Fstatusquo percentages were obtained. Despite the re-scaling of the results between the 2003 and 2005 XSA’s due to the conversion of the tuning survey data in accordance to the new RV units, the present Mterm trajectories of female spawning biomass and yield under a low fishing mortality regime confirm the advice from the 2003 assessment that the prevail of stock recovery on a foreseeable future is dependent of an average medium term catch level of 5 000 tons.