Spatial and temporal genetic patchiness in marine populations and their implications for fisheries management

A degree of genetic patchiness has been demonstrated in a variety of marine populations. When this "chaotic genetic patchiness" exists, populations a few kilometers apart may differ genetically by as much as those hundreds of km apart. Such genetic patchiness could be caused by any of several factor s, including natural selection acting on a local level before or after sett lement, and genetic drift before settlement. Hedgecock's "sweepstakes-chanc e matching hypothesis" addresses the latter explanation, and is based in pa rt on the observation of reduced genetic variability in young-of-the-year, relative to adult populations. This reduced genetic variability among recru its suggests that surviving young-of-the-year are the products of spawning by only a small fraction of the adult population, which, according to Hedge cock's hypothesis, happened to produce their offspring at a place and time that was suitable for survival. The succession of such cohorts would then l ead to the shifting genetic mosaic that is characteristic of marine populat ions displaying chaotic genetic patchiness. If generally true, this phenome non has implications far all forms of fisheries management, including marin e harvest refugia. To the extent that spawning success is spatially unpredi ctable, fisheries management should practice a degree of "spatial bet-hedgi ng." That is, within a biogeographical region of potentially panmictic larv al transport, spawning biomass should be conserved broadly, in an attempt t o ensure that propagules are available when and where favorable conditions for survival happen to occur.