Evol Ecol Res 16: 133-142 (2014)     Full PDF if your library subscribes.

Contrasting evolutionary and ecological management objectives in the context of sustainable harvesting

Dunja Jusufovski and Anna Kuparinen

Department of Environmental Sciences, University of Helsinki, Helsinki, Finland

Correspondence: D. Jusufovski, Department of Environmental Sciences, University of Helsinki, PO Box 65, FI-00014 Helsinki, Finland.
e-mail: dunja.jusufovski@helsinki.fi


Background: Harvesting of large, old fish can induce evolutionary changes in fish life histories (e.g. reduce age and size at maturation). Although reducing phenotypic selectivity of fishing can minimize the evolutionary impacts of fishing, this can lead to overfishing of immature individuals. The fishing strategy that aims to secure sufficient recruitment for the next generation, and thus targets solely the adult proportion of the population, is called the ‘spawn-at-least-once’ policy. However, this strategy conflicts with the attempt to avoid fisheries-induced evolution.

Questions: What are the ecological and evolutionary impacts of the prevailing hake fishing strategy that can be characterized by low phenotypic selectivity, compared with a strategy that uses a spawn-at-least-once policy? How do these two fishing strategies contribute to the sustainability of hake fisheries from both the ecological and evolutionary perspectives?

Methods: We address the questions using a case study, the European hake fishery. We simulate the eco-evolutionary dynamics of European hake populations under two alternative fishing strategies. The simulation approach is individual-based and describes individual life histories through von Bertalanffy growth curves and life-history invariants. We implemented the two strategies through two alternative fishing selectivity curves: (1) a low selectivity strategy estimated from current European hake fishing, which targets equally both immature and mature individuals, and (2) a spawn-at-least-once strategy of selectivity, which targets mature individuals.

Key assumptions: Growth histories and vulnerability to fishing do not depend on the sex of an individual. Reproductive success depends on female body size. Mature individuals have higher natural mortality owing to the survival costs of reproduction. The model does not incorporate any differences between geographical areas or any behavioural adaptations that may vary among fish.

Conclusions: The two fishing strategies showed opposite responses at the population and phenotypic levels. The spawn-at-least-once policy resulted in life-history evolution towards earlier maturation and smaller adult body size, but the population abundance remained high. In contrast, the prevailing low-selective fisheries strategy led to large reductions in population abundance but no evolutionary changes in life histories.

Keywords: age at maturation, European hake, fisheries-induced evolution, fishing, spawn-at-least-once.

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