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Think Tank: Digging for data

Researchers aim to take the guesswork out of lobster habitat, harvests

By Lauren Kramer
November 01, 2010

American lobster is one of the most important fisheries in the United States in terms of value. Landings in 2008 totalled 81.8 million pounds valued at $306.2 million. Two thirds of that came from Maine, which has accounted for the majority of American lobster landings for 27 consecutive years and employs thousands of fishermen.

In an industry this significant, it makes sense to track and predict what lobster numbers will be on a year-to-year basis. But the task of predicting the crustacean's abundance and distribution has, until recently, ignored environmental variables and habitat, says Dr. Andrew Thomas, professor of oceanography at the University of Maine School of Marine Sciences in Orono, Maine.

"Lobster fisheries managers
 have typically used stock assessment models to help them with their strategies," he says. "In the stock assessment model they try to guess how many lobsters are out there based on lobster data from fisheries and scientific surveys. This includes a fisheries recruitment component that tries to guess how many lobsters will grow up to a legal size of 83-millimeter carapace length. However, the whole Gulf of Maine is treated as a single unit."

Until recently, no environmental data has contributed to this model, but that's about to change. Thomas and his team of four other principal investigators are entering the final year of a three-year research project, an environmentally aware and spatially explicit stock assessment model paid for with a $430,000 grant 
from NASA.

The research consists of using water temperatures, currents and winds to predict the number of lobster larvae and where they will settle after they hatch. Then bottom habitat, temperature and salinities are considered to define space patterns for lobster recruitment.

"In their larval stage lobsters are plankton, and they're affected by currents and temperature," Thomas says. "From the stock assessment model we know what kind of habitat lobsters prefer, and our circulation model uses information on temperature and wind in the Gulf of Maine to forecast larval transplant and settlement. By adding environmental variability to lobster information we can hopefully make the guesswork more accurate and predict the most likely settlement places."

While their research has not yielded any surprises to date, it will allow decisions to be made regarding the impact on lobsters of changing environmental properties, or of the impact of a catastrophic event in one location, such as an oil spill.

"We're in a position that if we have a major oceanographic anomaly, that information will be fed into the fisheries model and will allow us to make a more accurate assessment of what the fisheries data will look like and provide space context to this information," he says. "One region of the Gulf of Maine does not necessarily behave the same as a place 50 kilometers away. On the flip side, if we have a good or bad year with lobster fisheries, we can look back into the oceanography data and use it to try and explain why that happened."

While University of Maine 
scientists are studying the environment and its effect on lobster distribution, Diane Cowan at The Lobster Conservancy in Friendship, Maine, has spent the last 18 years examining lobster growth. The research has been frustratingly gradual and highly variable because it takes a lobster anywhere between seven to 11 years to 
 reach harvestable size, she says.

"There's no way to age a lobster the way you can with other animals' hard parts because they shed all their hard parts when they molt," she says. Cowan has inserted tiny tags the size of a grain of sand inside the muscle tissue of up to 20,000 wild lobsters to try to determine age. "It's a data nightmare, and I'm not sure we really need to know how old they are," she says. "The way we manage lobsters by size is a decent proxy, and it's OK to do it that way."

However, Cowan believes the size limit for harvesting lobsters is too small. "The minimum legal size is one full molt group smaller than the size at which half of the animals are mature. To me, I don't care how old the lobsters are," Cowan says. "You try to make it so that some of the animals at least get to reproduce before they're captured. It's not wise to catch too many lobsters before they have a chance to reproduce."

The mark recapture program delivers important information to fisheries scientists, adds Cowan.

"Those scientists who use age-specific models still want the lobster age data to manage fisheries, and it's a good indicator of how well the lobsters are doing in the years before they reach harvestable size," she says.

Her research costs $130,000 a year but has never achieved this level of 
 funding. In the past, donations
 have come from the Darden Restaurants Foundation, Sea Grants from Maine and New Hampshire and community and private foundations, among others. This year the research is being funded by New England Biolabs Foundation, Maine Community Foundation, Davis Conservation Foundation, UpEast Foundation and contributions by members of The Lobster Conservancy.

Cowan's fascination is with the general well-being of the Maine lobster population and how well it is surviving year by year. "I'm really interested in who is with whom, whether they move and how far. One other thing you get out of marking individuals is knowledge about where they're living, how they're growing and how they're interacting," she says.

 

And happy lobsters produce a happy fishery.

 

Contributing Editor Lauren Kramer lives in British Columbia

 

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