ICES advises on the basis of the MSY approach a TAC of not more than 54 000 individuals of salmon. As the perception of the stock status has not changed markedly since last year’s assessment, the advice for the fishery in 2013 is the same as the advice given in 2011 for the 2012 fishery and, therefore, a decrease in exploitation with respect to the TAC implemented in 2012 is required.
The share of the total catch that is mis- and un-reported was estimated to be about 30% in 2011. Reducing these unaccounted removals would allow a higher TAC recommendation.
Salmon management should be based on the assessments of the status of individual stocks in the rivers. Fisheries on mixed stocks that cannot direct fishing only to those stocks that are close to or above their targets, present particular threats, and effort in such fisheries should be reduced. Fisheries in open-sea areas or coastal waters are more likely to pose these problems than fisheries in estuaries and rivers.
Salmon stocks in the rivers Rickleån and Öreälven in the Gulf of Bothnia, Emån in southern Sweden, and in a majority of the rivers in the southeastern Main Basin are especially weak and need longer-term stock rebuilding measures, including fisheries restrictions, habitat restoration, and removal of physical barriers. In order to maximize the potential recovery of these stocks, further decreases in exploitation are required along their feeding and spawning migration routes. The offshore fishery in the Main Basin catches all weak salmon stocks on their feeding migration. The coastal fishery catches weak stocks from northern rivers when the salmon pass the Åland Sea and Gulf of Bothnia on their spawning migration.
Assessment ModelQuality consideration
A considerable amount of total catches consists of estimated unreported catches (Table 22.214.171.124), which introduces uncertainties in the assessment. Catch per unit effort in the Polish offshore fishery and deviations in the reported species composition between Polish and other countries’ longline fisheries indicate large-scale misreporting of salmon as sea trout in the Polish fishery, and this misreporting constitutes a significant amount of the unreported catches (Table 126.96.36.199). However, there are some indications that the presented misreporting in the Polish fishery may be overestimated, especially in recent years. Internationally coordinated landing inspections are probably necessary to minimize the presumed substantial mis- and unreporting of catches in the offshore longline fishery.Scientific basis
The assessment uses a Bayesian estimation procedure. This technique allows an explicit incorporation of prior knowledge (from previous studies, literature, and/or expert opinions) about parameters in the assessment. With this approach uncertainties about estimated quantities are formulated as probability distributions.
The estimation of potential smolt production capacity is based on expert knowledge (prior information) and the spawner/smolt estimates (river-specific stock–recruit relationships) which are derived by fitting the assessment model with various data. The model incorporates new information annually and, thus, updates both smolt production historically and the potential smolt production capacity for each river. Inclusion of new information causes annual changes in these as well as in other parameter estimates.
|Working group report