Fisheries-induced evolution of cannibalism

Introduction

Natural populations react to harvesting by showing demographic, phenotypically plastic, and evolutionary responses. The understanding that evolutionary responses to fisheries can be rapid is supported by observational, experimental, and modeling studies. To date, however, research on fisheries-induced evolution has mainly focused on a limited number of life-history traits, including maturation schedules, growth rates, and reproductive investments. Consequently, selective changes in other traits, especially in those related to ecological interactions, have been largely ignored. Cannibalism is such an interaction that is especially frequent in fish populations: many fish species grow considerably in size during their life, which facilitates the predation of small fish by large conspecific fish. The aim of this project is to understand which ecological factors drive the evolution of cannibalism and how this is affected by fishing.

Methods

I use a physiologically structured population model (PSPM) to study the ecology and evolution of Arctic char populations. This species is commercially harvested in some parts of its circumpolar distribution and has a highly variable life history and ecology. Several instances of cannibalism have been documented in Arctic char. The PSPM describes the ecological and bioenergetics processes an individual undergoes throughout its life as a function of its physiological state and the state of its environment. The latter, in turn, is influenced by the joint impact of all individuals in the population. This feedback shapes the selection pressures that drive evolutionary change.

Results

Char populations with a low cannibalistic tendency evolve to a rapid life history with a low size at maturation and without post-maturation growth. The evolution of cannibalism in such populations is hampered by the low maximum size of individuals. An alternative life-history strategy evolves to a high level of cannibalism, a large size at maturation, and substantial post-maturation growth allowing individuals to reach large maximum sizes. Introducing mortality costs for cannibals stabilizes the selection for cannibalism. Harvesting individuals from populations dominated by a cannibalistic life history strategy is expected to increase their cannibalistic tendency. This leads to higher exploitation and stock collapse at lower fishing mortality rates than for non-cannibalistic populations, or to populations in which cannibalism does not evolve.

Conclusions

These results indicate that incorporating cannibalism in fisheries models does not change the predicted population response to harvesting in a qualitative manner. However, when cannibalism evolves, populations become more vulnerable to harvesting and collapse at lower fishing mortality.

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.

Last edited: 02 February 2016