The first season of a two-year lobster research project co-sponsored by Sea Grant and Island Institute was completed last fall.
The aim of the study is to improve trap-based methods of quantifying lobster, by employing newly developed mark-recapture methods. Estimates of abundance by these new methods are to be ground-truthed against diver-based counts.
The research team, lead by Dr. Rick Wahle of Bigelow laboratory, benefited from assistance by local fishermen. Wahle’s assistant, Mike Dunnington, along with Nate Geraldi and Corrie Roberts of the Island Institute, carried out the project.
The study was conducted outside of Carver’s Harbor, Vinalhaven, from June through December 2001, using 64 non-vented research traps set in a grid pattern over a square kilometer area. The research traps were set every four weeks for four three-day soaks. All captured legal and sublegal lobsters were tagged, measured and released. The tags, small plastic yellow or green streamers inserted between the carapace and abdomen, are retained through the annual lobster molts. Each tag contains a toll-free number on one end and an identification number on the other.
The research team completed over 250 dives in the study area in order to obtain lobster abundance estimates on the sea floor. Maps of the substrate (bottom) in the study area were generated using sidescan sonar. The sonar enables the determination of the substrate type — sand, mud, cobble and ledge. Finally, sea sampling of the commercial catch was conducted in the same square kilometer with the assistance of lobstermen.
Diver-counts done on sand, ledge and cobble were compared to the areas of these substrates determined from the sonar. Through the comparison it will be possible to determine whether the trap-based estimates of abundance are accurate.
Preliminary results show that the abundance estimates from the non-vented research traps are similar to the “ground truth” observations: from 25,000 to 50,000 lobsters within the area, depending on the time of season. The promising initial results suggest that trap-based mark-recapture methods used in this way maybe a good way to estimate lobster abundance.
Another objective of the study is to determine movement and growth of lobsters after release outside of the study area. Results are completely dependent upon cooperation from commercial lobstermen. Lobstermen who catch tagged lobsters can call the phone number on the tag and report the tag number, size of lobster, location and date of capture.
Information about the movements of tagged lobster is an excellent opportunity toward understanding lobster behavior in the Gulf of Maine. It allows movement to be calculated and mapped over a much larger scale.
Over 300 tags have been called in since mid-June. Some of the callbacks have tracked lobsters’ movements as far as Matinicus and Sprucehead. (The record breaker was a call report of a tagged lobster from a Wal-Mart in Wisconsin!)
As results emerge they will be available on the Island Institute’s web site, www.islandinstitute.org. A feature of the web page will be an interactive map (eAtlas) that will give information on date of captures, distance moved, and size of the lobster. The project will continue in June for its second and final year. For further information, contact Nate Geraldi at the Institute, (207) 594-9209, ext. 125.