Benefits To Migratory Fish Populations Of Entrainment And Its Potential Role In Fisheries Collapse

According to the entrainment hypothesis, traditional migratory routes develop in fish populations through social interactions. First-time migrants learn migratory routes by following experienced conspecifics and, by repeating the migration, contribute to guiding future cohorts along the same route. The loss of collective memory of migratory routes may be a precursor to fisheries collapse. The survival value of entrainment has not been convincingly demonstrated, and this possibly explains why there has not been greater interest in this putative migratory mechanism. I propose that the relative frequency of demonstrators of alternative contingents provides information to first-time migrants on relative survival rates. Using simulation, I show that a population in which contingent adoption is regulated by entrainment can achieve higher overall survival rates than a comparable population with fixed rates of contingent adoption in the situation where mortality rates differ among contingents. In certain cases, the advantage could be even larger in the presence of fishing mortality. I also compare the responses of the entrainment-based and fixed-rate migration populations in a scenario intended to mimic the cessation of fishing after a period of high fishing mortality, such as might occur after the collapse of a fishery.