Commercial Fisheries News - January 2001

Molting and egg production

Recently, lobsterman James F. King found two freshly molted female lobsters alongside their molt shells in his traps. He saw that there were eggs attached to the empty shells. The females had molted before their eggs hatched — functionally aborting their broods.

Although scientists have observed female lobsters shedding full complements of healthy eggs in the laboratory, it is interesting to learn that this also occurs in nature.

As far as I know, there are no available data on the frequency of occurrence of female lobsters shedding their broods. However, data exist on individual females observed to molt while carrying viable eggs. All of the females were small — probably first-time spawners.

The general problem that lobsters face is that in order to reproduce successfully, female lobsters must brood their eggs between molting events. The mechanisms that control the coordination and reconciliation of molting and reproduction are unknown.

Lobsters continue to grow throughout their lives. Therefore, the relationship between the timing of molting (growth) and spawning (egg extrusion) changes as female lobsters grow older. The time interval between successive molts is greater for larger females. It is therefore highly unlikely that a large female will molt while brooding.

Observations on the timing of molting and spawning events offer clues to relative contributions to egg production. Female lobsters at the smaller end of the maturity spectrum take one of two courses of action. They either molt early in the summer and spawn in the fall, or they molt in the fall and spawn the following summer. These females typically molt again soon after their eggs hatch.

Larger females molt less frequently and therefore have more time for reproduction. Female lobsters weighing more than four pounds also follow one of two spawning patterns. First, the female molts in one year and spawns in the following year. After hatching, she spawns again, either in the same year or in the following year.

To fertilize the eggs without molting, the female uses sperm she has stored since a previous mating or she mates again while she is hard shelled. Whether a female mates again is dependent on the quantity of sperm she is carrying and the maturation stage of the eggs she is producing in her ovaries.

In addition to the reduced likelihood of molting during brooding, various other factors favor egg production in large females. Large female lobsters are more fecund than small females because they produce more broods in the same time interval and carry more eggs on their larger abdomens and the eggs themselves have a higher energy content.

Therefore, depending on the smallest females for egg production is not a favorable option. Fortunately, the protection of large female lobsters continues to be supported by much of the industry.

Special thanks to James F. King, F/V Leslie K, and Carl LoBue of the New York State Department of Environmental Conservation, Bureau of Marine Resources for providing information on the female lobsters shedding their broods in nature.

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