Theoretical Consequences of the Adopted-Migrant Hypothesis in a Herring Metapopulation

Forage fish are vital to marine ecosystems and fisheries. In British Columbia, Pacific herring (Clupea pallasii) support important commercial, recreational and food fisheries, and iconic marine and terrestrial predators. Conservation of Pacific herring is a growing concern, and management practices in British Columbia are designed to be precautionary. However, stakeholder perspectives differ on Pacific herring population structure within management areas. In particular, local knowledge suggests fine-scale spatial population structure, realized in differential habitat usage and spawn timing. By contrast, genetic stock identification indicates well-mixed, homogeneous populations on the scale of management regions. To reconcile these observations, we developed a spatially explicit metapopulation model that incorporated the adopted-migrant hypothesis to describe recruitment. The adopted-migrant hypothesis provides a behavioural mechanism for the maintenance of spatial population structure whereby juvenile fish are ‘entrained’ into distinct adult populations by social learning. Importantly, no genetic population structure need be assumed. To assess support for our use of the adopted-migrant hypothesis, we compared model simulations to observed patterns of population abundance and spatial habitat utilization among Pacific herring in British Columbia. To understand potential population consequences of recruitment-by-entrainment, we performed model simulations under realistic fishery and ecological scenarios and compared these to management and conservation targets.