Fisheries-induced disruptive selection

Pietro Landi assesses how the interplay between natural and artificial selection, in the simplest setting in which fishery and stock co-evolve, could lead to trait diversification due to disruptive selection.

Introduction

Commercial harvest is recognized as inducing adaptive responses of life-history traits in fish populations, in particular, shifting the age and size at maturity due to directional selection. In addition to evolution of the target stock, the fishery itself can adapt, in terms of fishing policy, technological progress, fleet dynamics, and adaptive harvest. The aim of this study is to assess how the interplay between natural and artificial selection, in the simplest setting in which fishery and stock co-evolve, could lead to trait diversification due to disruptive selection.

Methodology

We build an eco-evolutionary model for a size-structured population, in which both the stock maturation schedule and the harvest rate are adaptive, and fishing is subject to a selective policy on fish size and maturity stage. Using numerical bifurcation analysis, we study the effect on disruptive selection of fishing policy with different fishing mortality and degree of harvest specialization, life-history trade-offs of early maturation, and demographic and environmental parameters.

Results

We report the following findings. First, fisheries-induced disruptive selection is readily caused by commonly used policies, and occurs even for policies that are not specific for fish size and maturation state, provided that the harvest is sufficiently adaptive and large individuals are targeted intensively. Second, disruptive selection is more likely in stocks in which selective pressure for early maturation is naturally strong, provided life-history tradeoffs are sufficiently high. Third, when a fish stock is overexploited, fisheries targeting only large individuals can slightly increase sustainable yield by diversification (although such an increased yield is still lower than the maximum sustainable yield under low fishing mortality, for which selection is not disruptive).

Conclusions

Fisheries-induced disruptive selection seems to be a rather plausible phenomenon. Our results can be taken into account for the evolutionarily informed management of fisheries.

Figure 1. Evolutionary scenarios of fisheries-induced disruptive selection.

Supervisors

Cang Hui, Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch, University, Matieland 7602, South Africa
Ulf Dieckmann, Evolution and Ecology Program (EEP), IIASA

Note

Pietro Landi of the Politecnico di Milano, Milano, Italy, is an Italian citizen. He was funded by IIASA's South African National Member Organization for the YSSP.

Please note these Proceedings have received limited or no review from supervisors and IIASA program directors, and the views and results expressed therein do not necessarily represent IIASA, its National Member Organizations, or other organizations supporting the work.


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Last edited: 23 March 2015

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