DMC research aims to validate lobster aging technique

Dr. Rick Wahle and graduate student Carl Huntsberger are testing a new technique for aging lobsters at the University of Maine’s Darling Marine Center in Walpole.

Wahle pointed out that unlike fish, mollusks and trees, lobsters and other crustaceans molt, casting off their skeletons and discarding any outer signs of growth bands.

That means a lobster’s age is estimated solely on size, but it’s a rough estimate because a lobster’s growth rate is affected by ocean conditions. Not knowing a lobster’s true age is a problem for scientists and fishery managers trying to measure the animal’s health and stock sustainability.

Recent research by Dr. Raouf Kilada, of the University of New Brunswick, has shown that lobsters and other crustaceans have internal structures that exhibit growth pattern similar to tree rings.

Dr. Kilada found tree-ring like microscopic bands, less than 1 millimeter thick, within the gastric mill of lobsters and crabs, a part of the stomach that grinds up food. He is now working with labs like the Darling Marine Center to validate that they do indeed show annual growth.

Kilada visited the DMC this winter to share his technique with Wahle and Huntsberger.

“At this point we are able to dissect lobsters that have been held in captivity for three years after staining the gastric mill with a florescent dye, which marks when we began our observations,” said Huntsberger, a graduate student in Dr. Wahle’s lab who is processing the samples.

The growth bands he is examining are located in the ossicles, tiny plate-like structures in the stomach that facilitate grinding of food. These are embedded in epoxy then cut into 150 micron sections to count the bands under a microscope. (For reference, a human hair is about 75 microns.)

Huntsberger, who said that preliminary data was proving that the bands show annual growth patterns, was glad to have Dr. Kilada’s hands-on instruction to perform the processing, which Kilada has perfected through many hours of trial and error.

“He had anecdotes about difficulties he has had with processing samples,” said Huntsberger. “I can only imagine how tedious that must have been.”

The lobster aging project is jointly funded by the Maine Department of Marine Resources and Maine Sea Grant.