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Case Study 3, Approach 4, Analysis of dependency of salmon productivity on environmental variables

Objective

The objective of approach 4 is to improve short-term predictions of the M74-syndrom (and potentially also those of post-smolt mortality), based on sprat stock predictions and relevant environmental variables and then to update the OM to facilitate the evaluation of alternative mgmt ref. points and HCR’s that take M74-risks into account based e.g. on the indices of sprat abundance.

Results

The relevant environmental data have been compiled (months 1-36), but the preliminary analyses indicate that this approach may not be a modelling priority in the CS (Grzebielec 2007).

One important paper related to approach 4 has however been recently finalized (Michielsens et al. 2006). The paper explores how the M74 mortality affects the productivity and the stock-recruit relationship of the salmon stocks. The results have also been taken into account in the analysis of the river specific reference points (Approach 3).

Michielsens, C.G.J., Mäntyniemi, S. and Vuorinen, P.J. (2006). Estimation of annual mortality rates caused by Early Mortality Syndromes (EMS) and their impact on salmonid stock-recruit relationships. Canadian journal of fisheries and aquatic sciences, 63: 1968-1981.
Abstract: In this paper, we demonstrate how information from broodstocks can be combined with lab information on alevins to obtain annual stock-specific mortality estimates from early mortality syndromes (EMS) using a probabilistic approach, how a hierarchical model structure can be used to predict these mortality rates for related, partly sampled, or unsampled stocks, and why these estimates should be used to remove the effect of this mortality on stock–recruit estimates. The approach has been illustrated for Atlantic salmon (Salmo salar) stocks in the Baltic Sea affected by the M74 syndrome. Results indicate that data on the proportion of M74-affected females, commonly used to approximate M74 mortality, overestimate actual M74-related mortality because of a declining trend in mortality among offspring of these females. The stock-specific M74 mortality estimates are used to account for nonstationarity in the stock–recruitment relationship caused by this fluctuating mortality. Because hierarchical meta-analyses assume exchangeability, the effect of M74 mortality is removed before including these stocks within hierarchical stock–recruit analyses of Atlantic salmon stocks, which are commonly unaffected by M74 mortality. Failure to remove the effect of M74 mortality on the stock– recruit data results in underestimation of the stock’s productivity and resilience to exploitation, especially in the case of stocks with steep stock–recruit curves.

Dissemination and References

Michielsens, C.G.J., Mäntyniemi, S. and Vuorinen, P.J. (2006). Estimation of annual mortality rates caused by Early Mortality Syndromes (EMS) and their impact on salmonid stock-recruit relationships. Canadian journal of fisheries and aquatic sciences, 63: 1968-1981.

Grzebielec, R. Statistical analysis of the dependence of smolt production for Baltic salmon on SST and other climate variables in 1987-2006 by management units 1-4. EFIMAS Working paper (in writing-up phase.

Grzebielec, R. Post-smolt survival of wild salmon in relation to SST and other environmental factors. EFIMAS Working paper (in writing-up phase).

 
efimas1/wp4/cs3/appr4/main.txt · Last modified: 2008/11/16 00:38 by admin
 
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