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Crustacean brawls caught on camera

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Going to pot: scientists are re-assessing their lobster traps
© Winsor H. Watson, III



Kitchen confidential: surveillance cameras crack down on lobster trap layabouts

Underwater video reveals lobsters behaving badly.

A lobster-pot is more like a Wild West saloon than a cunningly laid snare. Lobsters show up for food and a fight, and only the unlucky few get reeled in, underwater video footage is revealing.

Camera recordings show that lobster traps catch a mere 6% of the animals that enter them. The result suggests that lobsters’ rowdy behaviour could be confusing attempts to count and size them, and so to manage the fishery¹.

"Predicting the future of the population is difficult," says Stanley Cobb, who studies lobsters at the University of Rhode Island in Kingston. "Traps may not be sampling all parts of the population." Egg-bearing females, for example, seem to avoid them, says Cobb.

Lobster numbers are usually estimated from the catches of experimental traps. To gauge

The traps soon attracted a crowd of brawling crustaceans. "They hate each other," says Watson. "They compete outside the trap for the next opportunity to enter, and occupants fight off those trying to come in."

Traps have a ’kitchen’ where bait is kept. This leads to two ’parlours’ where lobsters are supposedly held. They also have emergency exits to let undersized animals out.

Lobsters, however, don’t play fair: "75% of them went right back out the entrance," says Watson. The few that were caught tended to be larger specimens that could fight off intruders, and were interrupted mid-meal. "We call it the restaurant hypothesis," Watson says.

What’s the catch?

"A lot of lobstermen feel that traps are really feeding stations," says Cobb. New England’s lobster fishery is in good health - perhaps, says Cobb, because of all the bait that fishermen put out. Lobster catches worth about $200 million are landed each year in Maine alone.

But researchers are not sure how long the good times can go on. "We catch about 90% of lobsters bigger than the legal size limit. I’m concerned we’re fishing too heavily," says Watson. Catches are beginning to decline in the southern area of the fishery, and there are signs that disease is damaging the crustaceans.

Researchers would like to be able to read any warning signs, so that they can move to avert possible crashes, rather than have to repair a shattered fishery. To do this, they may need new ways of counting lobsters - one possibility Watson suggests is a trap that can catch multiple lobsters by moving them away from the entrance, "like a maze".


References

1. Jury, S. H., Howell, H., O’Gradt, D. F. & Watson, W. H. III Lobster trap video: in situ surveillance of the behaviour of Homarus americanus in and around traps. Marine and Freshwater Research, 52, 1125 - 1132 , (2001).
   
   

   JOHN WHITFIELD | Quelle: © Nature News Service
   

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