The role of “ larval retention” in life-cycle closure of Atlantic herring (Clupea harengus) populations

Following a short summary of the contribution of Hjort's 1914 paper to the subsequent studies on population richness of fish species, the literature on herring larval drift and transport in the northeast Atlantic is reviewed (including the early studies contributing to the Migration Triangle hypothesis, process oriented studies in the field, and oceanographic modelling work). The review indicates that the concept of larval transport, within the context of the Migration Triangle hypothesis (which addresses the location of spawning) and the Common Pool/Adopted Migrant hypotheses (which interpret the degree of population richness of Atlantic herring), is generally supported. In contrast, analyses of the ICES large scale herring larval surveys in the Norwegian Coastal Current, the North Sea, and the shelf seas north and west of Scotland and Ireland (as well as the similar survey off southwest Nova Scotia in Atlantic Canada) indicate that there is limited displacement in the centres of distribution of different length classes of larvae. Given that larval length is a proxy for age, the analyses suggest that during the first two to three months of the larval phase the Centres of Mass (CoMs) for the progeny of the different spawning areas are relatively fixed. The results support the interpretation that location of spawning is not defined in relation to transport of larvae from the spawning area to the juvenile nursery area, but rather due to the minimisation of drift and transport (i.e. “larval retention”) at the early life history stage (as outlined in the Member/Vagrant hypothesis). The minimisation of drift and transport in the areas of spawning are interpreted as being important to the definition of the spatial scale of philopatry (and thus life cycle closure) in herring populations.