Management of the American lobster fishery is inextricably linked to a thorough understanding of their reproductive cycle. In particular, it is vital to know when females reach sexual maturity, where they release their larvae, and how larvae are transported in the water column and where they settle to the bottom, as this information influences the distribution and abundance of lobsters. A major goal of this project is to identify the factors that influence where female lobster release their larvae. If this question can be elucidated, it will greatly facilitate and improve models of larvae transport that are currently being produced by a number of marine biologists and oceanographers (Incze et al., 2003). These data will be invaluable for aiding in the determination of potentially distinct regional lobster stocks, a critical component of an effective management strategy for the American lobster fishery.
Female lobsters incubate eggs on the ventral side of their abdomen for approximately 9 months. However, gestation time can vary between 6 and 13 months, because development of lobster eggs is directly dependent on temperature (Perkins, 1972). In theory, females could speed up, or slow down, egg growth and development by moving into warmer or colder water. In fact, it is generally accepted that female lobsters move inshore during the warmer months and offshore in the colder months in order to expose their eggs to temperatures that cause their eggs to hatch at an optimal time for larval growth and survival (Campbell, 1986). However, recent work by Cowan et al., (in prep.) discovered that, while there was considerable variability in the distance moved by different berried females, the temperatures they experienced were very similar; as was the amount of time it took for the eggs to hatch. Furthermore, no matter how they moved, lobsters experienced at least some portion of the incubation period at temperatures < 5C. This period of time at a very low temperature may serve two purposes; first, it may serve to synchronize their reproductive cycle (Aiken and Waddy, 1976) and, second, it may actually delay development so that the eggs will hatch at the best time for their survival. For example, if a female extruded her eggs on August 1st, and was exposed to a constant temperature of 11C, larvae would start hatching on February 10th, when there are potentially lethally cold surface temperatures, and very little, if any, suitable food. Therefore, the view that most lobster movements can be explained in terms of a drive to seek higher water temperatures may need to be reexamined. The overall goal of this project is to test the long-standing hypothesis that the movements of female lobsters serve to increase the number of degree-days they experience and thus shorten the time period between egg extrusion and hatching.