Abstract
Size structure of fish stock plays an important role in maintaining sustainability of the population. Size distribution of an exploited stock is predicted to shift toward small individuals caused by size-selective fishing and/or warming; however, their relative contribution remains relatively unexplored. In addition, existing analyses on size structure have focused on univariate size-based indicators (SBIs), such as mean length, evenness of size classes, or the upper 95-percentile of the length frequency distribution; these approaches may not capture full information of size structure. To bridge the gap, we used the variation partitioning approach to examine how the size structure (composition of size classes) responded to fishing, warming and the interaction. We analyzed 28 exploited stocks in the West US, Alaska and North Sea. Our result shows fishing has the most prominent effect on the size structure of the exploited stocks. In addition, the fish stocks experienced higher variability in fishing is more responsive to the temperature effect in their size structure, suggesting that fishing may elevate the sensitivity of exploited stocks in responding to environmental effects. The variation partitioning approach provides complementary information to univariate SBIs in analyzing size structure.
Highlights
Size structure plays an important role in maintaining reproductive potential and stability of a fish population
We found difference in fishing and temperature effect among regions (Fig. 2) and habitat types (Fig. 3)
We introduced the size-structure based approach relying on variation partitioning to quantify fishing and temperature effects on size composition of exploited fish stocks, instead of focusing on univariate size-based indicators
Summary
Size structure plays an important role in maintaining reproductive potential and stability of a fish population. Previous studies on quantifying fishing or temperature effects on the size structure of fish populations have been focused on univariate size-based indicators (SBI). European Commission Marine Strategy Framework Directive required regional (or local) fishery reports to provide the information of basic SBIs (e.g. the mean length) in order to improve the management and maintain the sustainable development[38]. It remains unclear whether these univariate SBIs could represent the entire size structure and the status of a population. The analysis with the North Sea cod, herring and plaice found L95 failed to reveal the effects of external forces on fish populations, as it was rather insensitive in responding to fishing mortality[36]
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