Discrepancies between population genetic structure and adult migration patterns in cod (Gadus morhua) and whiting (Merlangius merlangus): evidences for entrainment ?

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Whiting and cod are two closely related gadoids, sharing the same grounds in the northern European waters as well as most of their life-cycle features. Many studies have investigated the level of mixing of adults in both species for more than one century, using a wide spectrum of methods such as tagging experiments, parasitic tags, otolith analysis, meristics and morphometrics. This large amount of data is particularly valuable to evaluate the migration patterns of adults and to detect homing behaviour, but do not allow to draw any conclusion about the natal origin of the fish and thus to discriminate natal homing from entrainment. Since the last decade, several studies have depicted the population genetic structure of cod and whiting in the NE Atlantic, providing useful informations about the extent of gene flow between populations through the passive drift of eggs and larvae or the active migration of adults. Population genetic structure and adult migration patterns displayed substantial discrepancies, and the purpose of this talk is to review all these discrepancies reported in the literature for cod and whiting. The comparison of gene flow and adult migration patterns in both species offers a very interesting opportunity to disentangle natal homing from entrainment.