Advection-diffusion models of spiny lobster Palinurus gilchristi migrations for use in spatial fisheries management

摘要

Advection-diffusion models were constructed to simulate migration patterns of juvenile and adult spiny lobsters off southern South Africa. Models based on tag-recapture information collected between 1978 and 2005 (2665 tag recaptures) were used to quantify directional movements and to estimate distances moved along a bathymetric gradient. Sex, length at tagging, tagging area and time at large were the main explanatory variables considered. Empirical tests showed that tagging did not delay the onset of advective movements. Lobsters were advected from west to east, and no return migrations were observed. Advection was strongly size dependent, with juvenile and small mature individuals moving further than larger adults. Advection was also area dependent, decreasing from west to east, and lobsters at the easternmost site were not advected and did not receive immigrants from elsewhere. Juvenile lobsters tagged at a recruitment hotspot at the westernmost site migrated 100 to 250 km onto the Agulhas Bank (90% probability after 5 yr at large), or continued along the coast to more distant sites (400 to 900 km; 10% after 5 yr). This effect was stronger in males, but we could not detect a trade-off in growth rate. Two theories are advanced to explain these migration strategies: evolutionary effects of past range expansions and density dependence. A novel approach for quantifying migrations in spiny lobsters is demonstrated, for potential use in spatial fisheries management.