Commercial Fisheries News - July 2002
In June, as lobstermen wait anxiously for the start of the summer run of shedders, several questions often come up regarding molting. Let's take a look at some of them.
Q: What are some of the signs that lobsters will start molting?
A: Behavioral signs include increased activity and movements, as well as building shelters and barricading entrances. Physical signs include: softening around joints and at carapace's margin; growth of limb buds for regenerating missing parts; and darkening of the shell.
Q: Is there a size issue related to molting?
A: Actually, there are several. The smaller the lobster, the more frequently it molts. For example, a typical lobster embryo molts 35 times inside the egg and completes four molts in its planktonic stage. The number of molts before winter that first year depends on when the post larva settles to bottom. The post larva molts into a fifth stage when it settles to the bottom. If settlement occurs in July, the lobster will keep growing until November and may molt up to about once a month or about four more times. That's 35 times in the egg, four in the water column, one when it reaches the bottom, and four more times that season, totaling 44 molts before the lobster has reached one year of age! During the second year, juvenile lobsters molt about every other month from May through November, completing four molts in that year. After that, molts get further and further apart. A typical third- and fourth-year juvenile molts two or three times a year. Fifth- and sixth-year lobsters molt once or twice. By the seventh year, molting takes place no more than once a year. From then on, lobsters molt only once every two or three years. Ultimately, the frequency and time between molts depends on how long it takes the lobster to fill the empty space in its new, larger shell. The bigger the shell, the longer between molts.
Q: Is water temperature a factor?
A: Temperature has a great deal to do with when and how often a lobster molts. In the laboratory, scientists have speeded up the process to raise a one-pound lobster in two years by elevating temperature and providing adequate food. These fast-growing lab lobsters don't taste nearly as good as their wild counterparts, which typically take about seven years to reach a weight of one pound. Molting is seasonal. The bulk of the spring molt for the adult population occurs with the rapid increase in water temperature as well as daylight hours. The corresponding fall molt coincides with a rapid decrease in water temperature and shortening of daylight hours. Winter molting is rare, but it does happen. It takes longer for the new shell to harden in cold water. The duration to hardening depends on water temperature, nutrition, water quality, and the size of the lobster.