How Does Winter Mortality Determine Population Abundance and the Potential for Range Expansion for Species Near Their Poleward Range Limits?

It is important to understand the processes that control the abundance and distribution of marine populations, especially at the northern edges of their range. For example, blue crabs, Callinectes sapidus, in the northern Atlantic have been poorly studied in comparison to their southern counterparts. It is assumed that winter mortality defines the northern range limit and controls the productivity of the population. In order to understand the population dynamics of blue crab, which is a growing fishery in the north, we paired summer field sampling with overwintering mortality experiments.  These experiments determined the time to death of juvenile and small adult blue crabs under four different temperature and salinity regimes, which reflect realistic conditions in mid-latitude estuaries. Combining these results with field temperature and salinity data, we will predict winter survival in Great South Bay, a northern latitude lagoonal estuary and in Chesapeake Bay, a southern partially mixed estuary. The implications of these results are useful because regional quotas can be based on winter severity and the subsequent predicted survival rates.