Research Document - 2001/099
An assessment of the cod stock in NAFO Subdivision 3Ps in October 2001
By . Brattey, N.G. Cadigan, B.P. Healey, G.R. Lilly, E.F. Murphy, P.A. Shelton, D.E. Stansbury, M.J. Morgan, and J.-C. Mahé
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 on 1 April 2002 and evaluates alternative TAC options for the management year 1 April 2002 - 31 March 2003. Assessments prior to 2000 provided scientific advice on a calendar year basis, but the management year was changed during 2000 to begin on 1 April 2000 and end 31 March 2001. Sources of information available for this assessment were: reported landings from commercial fisheries (1959-March 2001), oceanographic data, a time series (1973-2001) of abundance and biomass indices from Canadian winter/spring research vessel (RV) bottom-trawl surveys, an industry offshore bottom-trawl survey, inshore sentinel surveys (1995-2000), science logbooks from vessels <35ft (1997-2000), logbooks from vessels >35ft (1998-2000), and tagging studies (1997-2001). 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 2001 - 31 March 2002 was not available. Several sequential population analyses (SPA) were carried out using reported commercial catches, calibrated with Canadian RV survey data, standardized annual catch rate-at-age indices for line-trawl and gillnet from the sentinel survey, and industry trawl survey data. In some SPA runs, the RV surveys were treated as two indices, one for the eastern and one for the western portion of the stock area, as described in Brattey et al (2000). Spawner biomass estimates for 1 April 2001 from the various sequential population analysis formulations considered covered a wide range, and no single SPA run was considered to best represent absolute population size; however, estimated trends in spawner biomass were similar. All the sequential population analyses indicated that spawner biomass increased during 1993-1998 but declined during 1998-2001. Spawner biomass is not being sustained by recent recruitment and the present assessment predicts that spawner biomass will decline further in 2001-2002 assuming the 15,000 t TAC is caught. However, a notable finding in this assessment was that the 1997 and 1998 year classes appear to be much stronger than those produced during 1991-1996. These encouraging signs of improved recruitment are likely to result in an increase in population biomass and spawner biomass in the next few years. Several risk analyses based on different SPA formulations were used to propagate the uncertainty in the estimated population size to 1 April 2003, under a range of TAC options for the 2002-2003 fishing season. Risk analyses indicate it is unlikely that spawner biomass will decline further in 2001-2002 at catch levels between 10,000 t and 20,000 t. The risk of exceeding the F0.1 limit reference level was greater than 5% in 2 of the 5 formulations for a TAC of 10,000 t and greater than 5% in 3 out of 5 formulations for a TAC of 15,000 t. The risk of exceeding the target reference point of half F0.1 was above 50% for 3 out of 5 formulations at a TAC of 10,000 t and above 50% for 4 out of 5 formulations for a TAC of 15,000 t. These risk analyses do not take into account uncertainties associated with the stock composition of the commercial catch, misreported catches and assumptions about natural mortality.
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