Research Document - 2000/134
An assessment of the cod stock in NAFO Subdiv. 3Ps in October 2000.
By Brattey, J., Cadigan, N.G., Lilly,G.R., Murphy, E.F., Shelton, P.A., Stansbury, D.E.
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 during 1 April 2001 and evaluates alternative TAC options for the management year 1 April 2001 - 31 March 2002. Previous assessments provided scientific advice on a calendar year basis, but in 2000 the management year was changed to begin on 1 April and end 31 March the following year. Sources of information for this assessment were: a time series (1973-2000) of abundance and biomass indices from Canadian winter/spring research vessel bottom trawl surveys, reported landings from commercial fisheries including a 6,000 t interim TAC during 1 January-31 March 2000, a third industry trawl survey on St. Pierre Bank, inshore sentinel surveys (1995-1999), science logbooks from vessels <35', and tagging studies. The fishery was still in progress at the time of the assessment and information from the 20,000 t TAC from 1 April 2000 - 31 March 2001 was not available. Sequential population analysis (SPA) was carried out using reported commercial catches, calibrated with Canadian research vessel survey data, and standardized annual catch rate-at-age indices for line-trawl and gillnet from the sentinel survey. The RV surveys were treated as two indices: the first survey index comprised spring (April) surveys conducted in strata in a known mixing area (Burgeo-Bank/Hermitage Channel) during 1993-2000 (thereby excluding surveys from this area during February-March when mixing with 4R-3Pn cod is thought to be more of a problem); the second survey index comprised survey catches from the remaining strata (1972-2000). The population biomass and spawner biomass on 1 April 2000 are estimated to be 76,000 t and 107,000 t, respectively. Spawner biomass on 1 January 1999 is estimated at 106,000 t, approximately 41,000 t lower than estimated for the corresponding time in the previous assessment. This downward revision is attributed to different treatment of the Burgeo Bank/Hermitage Channel portion of the survey index. Spawner biomass is not being sustained by recent recruitment and the present assessment predicts that spawner biomass will decline further in 2000 assuming the 20,000 t TAC is caught. Risk analyses indicates that there is a greater than 50% probability that spawner biomass will decline further in 2001-2002 at catch levels of 10,000 t or higher. The risk of exceeding 0.21 fishing mortality (the reference level used in the last assessment) with a catch of 10,000 t during 2001-2002 is 2% and with a catch of 20,000 t is 58%. The risk of exceeding 0.1 fishing mortality is 54% with a 10,000 t catch, and 99.6% with a 20,000 t catch. These risk analyses, though more comprehensive than those conducted in the past, reflect only the discrepancies between the survey indices and the particular form of the model used in the SPA; they do not take into account uncertainties associated with the stock composition of the commercial catch, misreported catches and assumptions about natural mortality.
Accessibility Notice
This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.
- Date modified: