DEMOGRAPHIC CONSEQUENCES OF AGE-SPECIFIC DISPERSAL IN MARINE FISH POPULATIONS

The fundamental model of marine fish population dynamics assumes that major events occur within the census area and that immigrants and emigrants can be safely ignored in the evaluation of stock dynamics. Dispersal is generally assumed to be associated with the movement of immature individuals away from their home area. Such a process may produce vagrants that have a low probability of surviving or successfully reproducing elsewhere. An alternative view, developed here, proposes that dispersal can have profound demographic consequences not only for the resident stock but for neighbouring stocks. A review of the fisheries literature and an analysis of data for two Scotian Shelf haddock stocks provided support for the hypothesis that the spatial magnitude of postlarval dispersal is generally density dependent, that vagrants flourish as juveniles outside the home area in neighbouring stocks, that they subsequently return home when mature, and that the recruitment dynamics of the neighbouring stocks are seriously misinterpreted when such movements are ignored. Additional implications of these findings, including synchronous recruitment patterns commonly observed between stocks, density-dependent growth, and groundfish stock management practices, are discussed.