Abstract
Climate forcing in complex ecosystems can have profound implications for ecosystem sustainability and may thus challenge a precautionary ecosystem management. Climatic influences documented to affect various ecological functions on a global scale, may themselves be observed on quantitative or qualitative scales including regime shifts in complex marine ecosystems. This study investigates the potential climatic impact on the reproduction success of spring-spawning herring (Clupea harengus) in the Western Baltic Sea (WBSS herring). To test for climate effects on reproduction success, the regionally determined and scientifically well-documented spawning grounds of WBSS herring represent an ideal model system. Climate effects on herring reproduction were investigated using two global indices of atmospheric variability and sea surface temperature, represented by the North Atlantic Oscillation (NAO) and the Atlantic Multi-decadal Oscillation (AMO), respectively, and the Baltic Sea Index (BSI) which is a regional-scale atmospheric index for the Baltic Sea. Moreover, we combined a traditional approach with modern time series analysis based on a recruitment model connecting parental population components with reproduction success. Generalized transfer functions (ARIMAX models) allowed evaluating the dynamic nature of exogenous climate processes interacting with the endogenous recruitment process. Using different model selection criteria our results reveal that in contrast to NAO and AMO, the BSI shows a significant positive but delayed signal on the annual dynamics of herring recruitment. The westward influence of the Siberian high is considered strongly suppressing the influence of the NAO in this area leading to a higher explanatory power of the BSI reflecting the atmospheric pressure regime on a North-South transect between Oslo, Norway and Szczecin, Poland. We suggest incorporating climate-induced effects into stock and risk assessments and management strategies as part of the EU ecosystem approach to support sustainable herring fisheries in the Western Baltic Sea.
Highlights
The EU Marine Strategy Framework Directive and the recently revised EU Common Fisheries Policy requires the development of sustainable ecosystem-based management strategies to reach the goal of Good Environmental Status
To test for indirect effects mediated through spawning-stock biomass (SSB), we examined the cross correlation factors (CCF) between SSB versus all-year Atlantic Multi-decadal Oscillation (AMO), winter North Atlantic Oscillation (NAO) as well as Baltic Sea Index (BSI) with lags of up to seven years (
Given our findings from cross-correlation and the underlying 1st order integrated recruitment and climate processes, we identified the following structure of the Cushing-type stock– recruitment model as a predictive generalized transfer function being extended by winter BSI: (1{B)loge(Rt)~mz(c0{c1B{c2B4)|(1{B)winter ð8Þ BSIt{1zd|(1{B)loge(SSBt{1)zgt where the term (1–B) indicates that 1st order differences have been taken for all variables, m is the mean term (corresponding to loge(a) in our original model), ci (B) the ith numerator polynomial of the transfer function for winter BSI and d is the 2nd numerator of the tgrta~ns1fe(r1{fuBn)c(t1i{onq1fBo2r)|SeSt,B.witThheet noise term is given by being the independent random error, and (1–Bd) = a differentiation parameter of order d = 0, 1, 2, ... years
Summary
One important constraint is the limited understanding of highly fluctuating recruitment processes of exploited fish populations and how they interact with exogenous factors. A major problem in assessing fish populations is that ecosystem effects are most often ignored when fisheries advice is formulated. One important limit set by latent factors is the carrying capacity of the ecosystem. This complex of limiting factors, which is most likely the shaping source of density dependence, can by itself be considered predominately driven by global-scale forces such as climate. Climate related changes in complex ecosystems can have profound implications for ecosystem sustainability in many ways and may challenge a precautionary ecosystem management. Taking into account climate forcing in models may significantly reduce the degree of non-explained ecologically induced variation and as such lowers predictive certainty
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