Report of the Workshop on Testing the Entrainment Hypothesis (WKTEST)

What is Entrainment? Fish can learn and memorise. Entrainment is a behavioural mechanism based on fish learning from other fish to ensure that migration routes and habitat uses are maintained over generations. It can explain conservatism as well as changes in life-cycle patterns. ICES SGRESP 2006 stated the entrainment hypothesis in a way that could be tested. The objective of the workshop was to screen a variety of case study populations to support or contradict the entrainment hypothesis.Evidence from case studies. None of the case studies were in conflict with the entrainment hypothesis. All showed overlap in size across ages as well as in space and time, which were necessary conditions for entrainment to happen. Entrainment relies on the behavioural interactions between groups of fish at certain critical periods during their life cycle. It could occur at any time in the life of a fish and for any type of migration. Major changes in life-cycle spatial patterns were related to major changes in abundance and in the proportion of naive to experienced fish. Highly abundant recruiting yearclasses could numerically dominate the standing stock, creating the opportunity for rapid changes of life-cycle patterns as a large fraction of the young fish would not be entrained to the classical migration pattern. Entrainment was demonstrated in herring by showing that spring- and autumn-spawning contingents were able to share progeny.