Lobster Research Questions
Intertidal zones: Lobster nurseries?
Diane Cowan of the non-profit Lobster Conservancy has been conducting research since 1992 on the presence of baby lobsters in rocky tidepools along the shore. She has tagged nearly 4,700 of the 7,000 baby lobsters she has found hiding under rocks and seweed. Using a hypodermic needle, she inserts a tiny tag one millimeter long into a small leg joint. Between five and ten percent of the lobsters she finds have been tagged before.
The purpose of her research, for which she is not paid, is to monitor the health of the lobster resources and to document the importance of coastal habitats in the lobster's life cycle. One surprise finding was to discover as many as eight tiny lobsters huddling together, despite the fact that lobsters in close quarters are known to cannibalize each other.
Q: How far do lobsters travel?
A: Most inshore lobsters migrate closer or further from shore depending on the seasons. They may move up to five or six miles in a year, going closer to shore in warm weather, and offshore to stable, deeper water in late fall.
Offshore lobster stocks may move greater distances. They may spawn in the deepest waters of the Gulf of Maine. A tagged lobster that traveled 273 miles between Maine and Nantucket holds the long-distance record!
Tagging and tracking studies reveal that many large lobsters congregate in the deeper canyons of the Gulf of Maine off the New England coast. Why is not yet understood, although some lobstermen claim that it is a breeding area for lobsters.
Sonar tagging may be the 21st-century alternative to traditional methods of tracking the movements of lobsters. Plastic tags coded with individual numbers have long been used to document where lobsters are released and captured. However, after one or two molts the tags fall off, and they can only provide information on the lobsters' destination, not how they got there. Sonar tags attached to lobsters' shells transmit back continuous messages about the lobsters' movements. Tagging studies done by both American and Canadian researchers indicate that the larger the lobster, the farther it is likely to travel. One lobster wandered 250 km!
Q: How much of a lobster's diet comes from trap bait?
A: Lobster bait is apparently an important food supply for lobsters. In one cooperative effort to learn more about the impact of lobster traps on lobster ecology, 48 lobstermen voluntarily removed their traps for 6 weeks from a productive lobstering area along the coast of Maine known as the "Thread of Life." Dr. Robert Steneck of the University of Maine concluded that baited lobster traps may actually be the largest aquaculture effort in the world. Shortly after all the traps were removed from the fishing grounds, the lobsters left, too. In another experiment called the "Fate of Bait," lobsters were observed crawling into and out of the forward chambers of lobster traps to feed on redfish, herring, and other bait fish or stealing pieces of bait through the slats of the traps. They were even observed crawling into empty traps.
Another modern method of scientific inquiry into lobster behavior is underwater videotaping. An underwater camera silently recording the action is much less inhibiting to the subjects than the presence of SCUBA-clad graduate students taking notes. And the graduate students seem to prefer it, too.
Q: How can we predict future lobster harvests?
A: Developing an early warning system for trands in lobster harvest: wouldn't it be great, if we could predict the size of a year's harvest from the strength of the pulse of larval settlement 5-7 years earlier? Researchers from the University of Maine, Bigelow Laboratory, the University of New Hampshire, the University of Rhode Island, and NMFS are collaborating with the lobster industry to develop such predictive tools as has been done in Australia with their wetwern rock lobster fishery.
Q: Crustacean age determination (How old IS a lobster?)
A: A basic problem for researchers is that there's no way to positively determine the age of lobsters or other crustaceans. They don't have growth rings and growth rates vary so much that size can be misleading. Scientists at Bigelow Laboratory are studying the accumulation of a brain pigment called lipofuscin that accumulates with age. It is relatively easy to quantify because it fluoresces under ultraviolet light. If it works, it would help scientists follow year classes through time.
Q: How do circulation and wind influence larval transport and patterns of settlement? (How much does Maine's lobster fishery depend on larval production elsewhere?)
A: Scientists find that settlement patterns vary a great deal locally and regionally in large part because of currents and wind. Still, they see that annual fluctuations in settlement in the Southwest Gulf of Maine and Rhode Island are more highly correlated than the two ends of the gulf itself. Scientists think that cold temperatures and/or circulation may limit larval settlement more downeast than they do to the south and west. This is relflected in lower harvests. Research also shows that wind-driven currents pile larvae up on windward sides of islands. Population densities on the west side of Damariscore Island, for example, are substantially higher than on the east side, as a result.