for Answers in Lobster Pounds
by Andrea Cohen, MIT Sea Grant
Telltale markers of the
lobster industry are endemic along much of the Maine coast: multicolored
buoys peppering the ocean surface, muscular lobster boats steaming
out to haul in traps, the bright crustaceans clambering over each
other in bubbling tanks at fish markets and seaside restaurants. But
there's one critical step in the process of bringing lobsters to market
of which most consumers are unaware, and that's the lobster pound.
These pounds are holding
areas in which lobstermen keep their catch to avoid glutting the market
with lobsters — and driving down the price per pound. In New England,
most lobsters are harvested in the autumn, when the animals' shells
are hard, and the weather has not yet turned too harsh for fishing.
Lobstermen generally begin filling the pounds in October and have
emptied them by April. The pounds themselves are dammed-off inshore
areas, often up to two acres large and a few feet deep. Aerators are
used to ensure good water quality, and ingoing and outgoing tides
assure nearly complete water exchanges. The lobsters are fed a feed
similar to the bait used to catch them.
Tlusty taking sediment cores.
courtesy of Michael Tlusty.
little is known about the ecological effects of placing perhaps
thousands of lobsters in an area that might naturally contain a
dozen crustaceans. So Michael Tlusty, a research scientist with
the New England Aquarium, has been studying the sediments in lobster
pounds. The research is funded by MIT Sea Grant.
"I'm very interested
in seeing how aggregating animals in certain areas impact the environment,"
says Tlusty. Having conducted such research with salmon in Newfoundland,
Tlusty was aware that no similar studies had been conducted with
lobsters. And while his salmon study was a $4 million project with
a full ecosystem analysis of how aquaculture interacts with the
environment, for the pound study, he opted for the far less expensive
approach of examining sediments. Tlusty's colleagues in the project
are Diane Cowan, senior scientist with the Lobster Conservancy in
Maine, and Jean Finney-Crawley, a researcher in the Department of
Biology at Memorial University of Newfoundland.
Basically, Tlusty is
looking at the feed being put into the pound, how much the lobsters
are taking up, how much they are excreting, and how much is being
deposited on the bottom. His work includes taking sediment cores
three times a year from each of 10 locations in Maine, each of which
has six to eight collection sites. These include pounds currently
in use and those no longer active, in order to make comparisons
between active and inactive pounds. (Tlusty notes that coastal waters
in Massachusetts are too crowded for pounds.)
"At each site we take
cores of the sediment to see how much organic matter has accumulated
in the layers. We also dig down 10 cm over a .25-square-meter area
and look at all the large organisms that we can find," says Tlusty.
"Finally, we skim the top 2 cm and look at the nematode [a type
of worm] abundance." Finney-Crawley is the nematode expert and her
effort, says Tlusty, will add an important additional layer to the
Back at the lab, Tlusty
burns the core samples at 500 degrees C to determine the amount
of organic matter present. The feed provided to lobsters in pounds
is typically 80-90 percent organic matter. Tlusty has found that
adult lobsters excrete roughly 40 percent of that organic matter,
and about 5 percent shows up in the sediments. "It's easy to account
for the loss from the feed to what comes out of the lobster," he
says. "But what is happening to that other 35 percent? Some of it
is washed out. Some is getting eaten by anthropods or bacterial
degradation. We are looking at this loss. If the lobsters are really
putting out 40 percent, why aren't we seeing higher levels in the
The answer, says Tlusty,
may be that the organic compounds are being flushed out of the pounds
with outgoing tides. This would also explain why the researchers
have not found a significant difference in the level of organic
compounds in active and inactive pounds. In looking at the presence
of larger animals, Tlusty has found many fewer mussels inside pounds
than outside of them—not a surprise given that they are a lobster's
What was a surprise,
says Tlusty, were some findings from lab experiments conducted to
learn about how lobsters process food. "People have suggested that
food can get through a lobster's digestive track in 18 hours," says
Tlusty. However, when the researcher starved the lobsters, then
fed them 3 percent of their body weight, he found that the animals
were still processing the same meal for 20 days.
Do lobster pounds impact
the environment? "Yes, just by the sake of damming the area you
are affecting it," says Tlusty. "Even if you don't put a lobster
in it, you are impacting the system." But, he also adds that he
and his colleagues have tried to identify inshore areas that look
like they could be used as pounds, and so far, these pristine areas
have all had higher levels of organic matter than the pounds. "When
you are dealing with the coast, you're dealing with these naturally
mucky areas," he says.
Tlusty is now anxiously
awaiting the nematode findings, which will present another way to
index how the ecosystem responds to any change in function. "The
abundance and diversity of nematodes gives you an idea of how much
a location is being disturbed," explains Tlusty. "Highly disturbed
or high energy places have nematodes that are 'colonizers,' while
calm and undisturbed sites have 'persisting' nematodes." Overall,
he says, he had expected the impact of pounds to be much greater.
But he's quick to add: "Anytime you look at nature you're going
to get surprised by something. I'm always surprised by doing this
work at how resilient ecological systems are."