Age of Lobsters

Research professor Rick Wahle and graduate student Carl Huntsberger are testing a technique at the University of Maine Darling Marine Center to determine the age of lobsters.

Unlike fish, mollusks and trees, Wahle says lobsters and other crustaceans molt — or cast off their skeletons, thereby discarding external signs of growth. That means a lobster’s age is estimated on size, but it’s a rough determination because ocean conditions affect the crustacean’s growth rate.

Knowing a lobster’s age is important for scientists and fishery managers seeking to measure the health of the fishery and sustainability of the stock.

Recent research by Dr. Raouf Kilada of the University of New Brunswick revealed that lobsters and other crustaceans have internal structures that exhibit growth patterns similar to tree rings. Kilada found tree-ring-like microscopic bands, only a fraction of a millimeter thick, within a lobster or crab’s gastric mill — a part of the stomach that grinds food.

Kilada recently visited the Darling Marine Center to share his technique with Wahle and Huntsberger.

The growth bands are located in the ossicles, which are tiny, bony, plate-like structures. To process a sample, ossicles are embedded in epoxy and cut into 150-micron sections. The number of bands can be counted using a microscope. (For reference, the thickness of a human hair is about 75 microns.)

Huntsberger, who is processing samples as part of a project funded by the Maine Department of Marine Resources and Maine Sea Grant, says preliminary data indicate the bands do show annual growth patterns.