The lobster is New England’s most commercially valuable marine resource (landings bring in the neighborhood of $250 million annually). Add to that figure the crustacean’s unquantifiable worth as a marketing icon and you¹ll begin to understand why it’s important to forecast the health of future crops.
It’s a task that falls somewhere between art and science. And some will tell you that success depends on not a small measure of luck.
A large part of the challenge involves the random nature of the marine environment. Early on, lobsters exist as microscopic particles, subject to the ebb and flow of wind, tide and temperature. If they survive for a month or two they’ll seek shelter on the bottom in fields of cobble and boulder. It will take another six to eight years before they grow large enough for the dinner table.
The odds of accurately predicting how many lobsters will survive the journey from hatch to catch are improved greatly by analyzing large quantities of information about the factors that influence settlement.
Over the years, biologists working with commercial fishermen, who observe lobsters every day, have expedited the data collection process.
“Working with the industry substantially improves the volume and quality of data we collect — vastly improving our forecasts,” said Richard Wahle, a scientist at the Bigelow Laboratory in Boothbay Harbor.
Wahle noted that lobstermen frequently call attention to changes in the marine environment that can lead to important new research.
For example, several years ago, lobstermen from across the region began noticing high numbers of juvenile lobsters residing in deep water.
This observation ran against conventional wisdom, which had long held that early stage lobsters almost exclusively settle in water less than 10 meters, where the temperature is relatively warm.
But few surveys had measured settlement in deeper places where temperatures might be also warm enough to trigger settlement.
For example, deep waters off Rhode Island are substantially warmer than equal depths in Maine. And, in places like the Bay of Fundy currents can keep the sea temperature surprisingly warm.
What’s more, previous studies deployed scuba divers to collect larvae between rocks and debris, a technique that is not safe in deep water.
To help fill in the research gaps, lobstermen Mark Parkhurst from Boothbay Harbor and Skip O’leary of Wakefield, R.I., partnered with Wahle and Carl Wilson of the Maine Department of Marine Resources to develop a device capable of evaluating the settlement of young lobsters in deep water.
They were supported by a $25,000 grant from the Northeast Consortium. Another Maine lobsterman, Norbert Lemieux, joined the project after it was underway.
Parkhurst built a device capable of sampling for larvae at depths greater than 10 meters. The design reflected improvements to larvae collectors used in a previous Sea Grant research project. It is made of 10-gauge vinyl-coated wire with 2-inch mesh and measures 24 by 33 inches in the floor and six inches deep.
For strength, the upper edge was bent over to clasp the wire cover. The bottom was fitted with oak runners and the floor and walls were lined with plastic mesh to help prevent newly settled lobsters, crabs and other organisms from escaping.
Before being deployed the devices were filled with cobbles ranging in diameter from 10 to15 centimeters. The cover was constructed of two-inch wire mesh that retained the rocks, but was designed not to deter lobsters or crabs from settling.
To learn how many larvae might be lost when the device was retrieved, divers seeded 20 collectors with 10 “stage V” lobsters each. Stage V is the first fully bottom-dwelling stage of the lobster’s life cycle. Larvae were obtained from the New England Aquarium.
The next morning, divers returned to cover 10 randomly selected collectors with the mesh. The intervening period gave lobsters the opportunity to stay or leave. If losses during recovery were substantial, the researchers knew there would be significantly fewer lobsters in the uncovered collectors.
If losses were significantly greater from uncovered collectors, researchers had planned to develop a mechanism that would cover the collectors upon retrieval. Then 40 collectors were distributed along the shore of two islands in the Midcoast area that are monitored annually, and known to receive high settlement over the past 17 years.
At the beginning of the settlement season, collectors were placed directly adjacent to the natural cobble surveyed at these sites. At the end of the season, divers sampled the sites as part of the government supported New England Lobster Settlement Index Survey (an annual diver-based suction sampling survey supported by Maine, Massachusetts and Rhode Island, and DFO Canada. Visit: www.bigelow.org).
The placement provided an opportunity to compare the performance of the collectors to natural settlement densities in the preferred habitat.
The results suggest that the densities of newly settled lobsters in the collectors is comparable to densities found in natural nurseries; and that it will not be necessary to incorporate a mechanism to cover the collectors prior to hauling.
For further information visit www.northeastconsortium.org.