Cruel new fact of crustacean life: lobster cannibalism

Researchers studying Maine's lobster population, booming in recent years amid warming waters and disappearing predators, have detected something never before seen in the wild: lobster cannibalism.

It has long been known that lobsters will attack and eat each other if confined together in a small space - hence the banding of claws on lobsters in supermarket tanks.

That aggressive behaviour had not been thought to occur in the wild, but with the increasing density of the crustaceans in the Gulf of Maine it seems big lobsters are feasting on little lobsters once the sun goes down.

"We've got the lobsters feeding back on themselves just because they're so abundant," said Richard Wahle, a marine sciences professor at the University of Maine, who is supervising the research. "It's never been observed just out in the open like this," he said.

Maine's lobster catch rose to a record 104 million pounds (45 million kilograms) last year, compared with 23 million pounds in 1981. The 2012 catch is expected to shatter that record as overfishing and other factors have led to the collapse of populations of cod, halibut and other groundfish that feed on lobsters.

Warming waters in the Gulf of Maine due to climate change have also bolstered the population even as the same phenomenon has led to more disease and lower populations in Long Island Sound and southern New England, Wahle said.

A graduate student working with Wahle, Noah Oppenheim, has been documenting the phenomenon using a special infrared camera that allows him to observe a juvenile lobster tethered with a rope to a spot on the ocean floor.

During the daytime, it is fish that typically feed on the tethered juvenile lobsters, but at night the researchers were stunned to see that most of the attacks on the small lobsters were by their larger brethren.

"The population of lobsters in Maine has skyrocketed and there have been some interesting changes in abundance, demographics and, we believe, behavior," Oppenheim said. "Eight out of nine times at night, predation is due to cannibalism."

Wahle said Canadian researchers studying the contents of lobsters' stomachs had also recently found evidence of cannibalism in the wild.

"There are these cases where encounters with each other are becoming so frequent, they result in more than just a bit of competition but in a predator-prey interaction," Wahle said.

Falling lobster prices due to this year's abundant catch have led to tensions between Canadian and US lobstermen. In August, New Brunswick lobstermen picketed processing plants and temporarily blocked shipments of inexpensive Maine lobster from being brought to the maritime provinces in Canada for processing.