Re-opening Criteria for Flemish Cap Cod: a Survey-based Method

One of the main difficulties in the assessment of closed fisheries is the lack of catch data needed to perform a VPA; nevertheless, assessment is necessary in order to advise for re-opening in the framework of the Precautionary Approach. In this situation, advise is usually based on survey trends, and the problem of not knowing the true abundance is translated to the advise as an increase of uncertainty. Nevertheless, when there was a calibration by a VPA assessment in the past, those catchability figures can be used to scale the current survey results and obtaining an estimation of the true abundance, more convenient for a precautionary advise. This paper proposes a way to manage survey information, using the Flemish Cap cod stock as an example. A stochastic simulation including estimates of errors in survey abundance and catchability at age is presented. The method, based in a stochastic design, yields a spawning stock biomass cumulative distribution ready to compare with Blim in probabilistic terms. Some weaknesses of the method as well as the quality of VPA-based assessment with low catches are discussed. Introduction NAFO Scientific Council has implemented the Precautionary Approach (PA) on Fisheries Management in late 90s based on several international agreements, such as the Code of Conduct for Responsible Fisheries (FAO, 1995) or the Agreement on the Management of Straddling Fish Stocks and Highly Migratory Fish Stocks (UN, 1995). Implementation includes recommendations on limit and target reference points, medium term considerations and risk, long-term requirements and criteria for re-opening fisheries. Scientific Council developed a PA framework in 1997 (Serchuck et al., 1997) to include definitions of limit, buffer and target reference points for biomass and fishing mortality. A review of progress on PA was recently developed in the Scientific Council Workshop on that issue (NAFO, 2003); the workshop included an evaluation of present framework as well as a review of methods for determining PA reference points and their application to NAFO stocks. Several fish stocks in the NAFO area are currently recognized as depleted, including some of them for cod supporting traditional fisheries, such as the northern stock and those of Div. 3NO and Flemish Cap. Evaluation of these stocks may include determination of their condition, classification of their stock status in relation to biomass limits and buffers, where available, and description and characterization of uncertainty and risk of the assessment. Taking into account that catches are, or should be, negligible in closed to fishing stocks, estimates of the fishing mortality (F) they support are not of main interest. The main concern for these stocks is the possibility of re-opening once they achieved some objective criteria related with the stock status. Those criteria should be stock specific. Flemish Cap cod is at present a collapsed stock; the reasons for this collapse are unclear, but there were three elements that had contributed to this situation: overfishing, a probable increase in catchability at low abundance levels, and a very poor recruitment since 1995. The stock is under fishing moratorium since 1999, although