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An XSA based assessment of beaked redfish (S. mentella and S. fasciatus) in NAFO division 3M

AuthorsÁvila de Melo, A.; Saborido-Rey, Fran ; Alpoim, R.
Issue Date2007
PublisherNorthwest Atlantic Fisheries Organization
CitationScientific Council Research (SCR) Document 07/47 (2007)
SeriesN 5399
AbstractThe 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. 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. Very high fishing mortalities until 1996 forced a rapid and steep decline of abundance, biomass and female spawning biomass of the 3M beaked redfish stock. With low fishing mortalities since then the stock decline was halted and the survival and growth of the existing cohorts allowed a discrete but continuous growth of 4+ biomass and female SSB from 1998 onwards. Meanwhile the income of a sequence of weak year classes (1991-1997) kept the 4+ abundance stable at a low level till 2001. However on the most recent years (2003-2006) a sequence of above average year classes from 1998 to 2002, each one greater than the previous, recruit each year to the 4+ stock, pumping abundance and biomass at the beginning of 2006 to a maximum and a second high of the 1989-2006 interval, respectively. At the same time the stock reproductive potential has increase substantially and above average year classes are being generated by parental female stock with biomass sizes well bellow the ones that produced the previous abundant 1989-1990 cohorts. Nevertheless these results of the present XSA assessment don’t change the perception of previous assessments, that this is still an unbalanced stock strongly leaning to the younger age groups and that female spawning stock biomass should be allowed to recover to the former 1989-1990 level, in order to stabilize the stock and the fishery at a safe zone. Short and medium term projections of female spawning stock biomass under a gradient of F status quo percentages, as well as SSB and yield medium term probability profiles under F status quo were obtained with the Mterm program of the CEFAS laboratory (Lowestoft/UK). In order to low the impact of retrospective bias on the Mterm projections, the XSA 2006/2005 average abundance and fishing mortality at age ratios estimated in the retrospective analysis were used to get a proxy of a retrospective-corrected population at age at the beginning of 2007 and of F status quo at age. The results of the present Mterm projections showed that the recent population growth and the survival of the abundant year classes that meanwhile joined the exploited stock will drive SSB over the 40,000 tons target in the short term if fishing mortality is kept at its present low level. Taking into account the recent biomass increase, a medium term constant fishing mortality at F status quo will imply in the near future a catch level not exceeding 10,000 tons
Description43 páginas, 11 tablas, 8 figuras.-- Scientific Council Meeting
Publisher version (URL)http://archive.nafo.int/open/sc/2007/scr07-047.pdf
Appears in Collections:(IIM) Artículos
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