The impact of seasonal movements by ovigerous American lobsters (Homarus americanus) on egg development and larval release
The American lobster (Homarus americanus) supports one of the most economically successful fisheries in the Gulf of Maine. The continued success of this fishery is attributed in part to vigilant broodstock conservation through the preservation of ovigerous (egg-bearing) females. Previous studies of ovigerous lobster movements indicate that some, if not most, display seasonal inshore-to-offshore movement patterns. While it has been assumed that these movements serve to expose eggs to thermal regimes that are optimal for development, this theory has never been rigorously tested. In Chapter 1, I present results from ultrasonic tracking studies designed to determine if lobsters in coastal New Hampshire waters exhibit this inshore-offshore pattern and also to identify where ovigerous females overwinter. In Chapter 2, I assess how the movements of ovigerous lobsters would influence the temperature regimes they experienced and thus the development of their eggs. I evaluate this question using a combination of laboratory and field experiments that expose animals to seasonally fluctuating water temperatures they would experience if they remained inshore or moved offshore; data from these experiments were then used to determine the influence of these thermal regimes on egg development, time to hatch, and larval survival. Finally, in Chapter 3, I present results from a study using experimental ocean drifters deployed in areas where ovigerous females were located when their eggs hatched, to determine where these larvae might drift. Ultrasonic tracking revealed that most lobsters move offshore in the fall and ovigerous lobsters tend to remain there until after their eggs hatch the following summer (Chapter 1). Eggs exposed to disparate thermal regimes (inshore and offshore) demonstrated that eggs carried by lobsters that moved offshore actually hatched later than those exposed to inshore temperatures (Chapter 2). Finally, most drifters released in offshore hatching locations were carried south or to offshore locations at the time when larvae would settle (Chapter 3). Taken together, these results suggest that seasonal movements of ovigerous lobsters have a strong influence on when and where eggs hatch and, subsequently, where larvae may settle. These findings have significant implications for population connectivity and management of the lobster fishery.
Biology, Zoology, Agriculture, Fisheries and Aquaculture, Oceanography
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