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Research Document - 2003/092

An assessment of the Atlantic cod (Gadus morhua) stock in NAFO Subdiv. 3Ps during October 2003

By Brattey, J., Cadigan, N.G., Healey, B.P., Lilly, G.R.,
Murphy, E.F., Stansbury, D.E., and Mahé, J.C.

Abstract

This document summarizes scientific information used to determine the status of the cod stock in NAFO Subdivision 3Ps off the south coast of Newfoundland. The current assessment provides revised estimates of the abundance of fish on 1 April 2003. Numbers-at-age are projected to 1 April 2004 by accounting for recorded catch up to the end of September 2003 and assumed catch for the remainder of the season to 31 March 2004. Sources of information available for this assessment were: reported landings from commercial fisheries (1959-March 2003), oceanographic data, a time series (1973-2003) of abundance and biomass indices from Canadian winter/spring research vessel (RV) bottom-trawl surveys, an industry offshore bottom-trawl survey (1997-2002), inshore sentinel surveys (1995-2002), science logbooks from vessels <35ft (1997-2002), logbooks from vessels >35ft (1998-2002), and tagging studies (1997-2003). The fishery was still in progress at the time of the assessment and complete information on catch rates and age compositions from the 15,000 t TAC from 1 April 2003 - 31 March 2004 was not available. Several sequential population analyses (SPA) were carried out using reported commercial catches, calibrated with various indices. Spawner biomass estimates for 1 April 2004 from the various SPA formulations considered covered a wide range (82,000 to 185,000 t), and as in the 2002 assessment, no single SPA run was considered to best represent absolute population size. However, estimated trends in 3+ population numbers and spawner biomass were generally consistent; the SPA's indicated 3+ population numbers increased during 1998-2000 but have tended to decline slightly during 2001-2003. Spawner biomass increased during 1993-1998, declined during 1999 to 2001, and increased slightly between 2002 and 2003. The 1997 year-class was well represented in fishery catches as 5 year olds and the 1998 year class also appears strongly in many stock indices, whereas catches and catch rates of many older age classes declined. The sizes of the 1997-1999 year classes were estimated to be lower than determined during the 2002 assessment; consequently, the outlook about the short-term productivity of the stock is less optimistic. Medium term (3 yr) deterministic projections were also conducted to provide managers with general insights into possible stock trends over the next three years. At a TAC of 20,000 t four of five formulations indicate that spawner biomass would decline by 1 April 2006. At a TAC of 15,000 t or 10,000 t three of five formulations indicated that spawner biomass would decline. The medium term projections do not take into account any uncertainties, such as those associated with the stock composition of the commercial catch, misreported catches and assumptions about natural mortality. The trends in the projections are particularly sensitive to recent changes in estimates of the proportion of females that mature at young ages and become part of the spawning population, as well as estimates of the 1997-1999 year classes and their subsequent survival and recruitment to the fishery.

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