Evidence of mating by sexually immature female American lobsters Homarus americanus (H. Milne Edwards, 1837) (Decapoda: Nephropidae)

Recent findings indicate that female American lobsters, Homarus americanus (H. Milne Edwards, 1837), are either reaching sexual maturity at smaller sizes than in the past, due to ocean warming or fishery-induced selection, or they are mating before they are sexually mature. To test the second hypothesis, we determined the mating status (i.e., presence of sperm in seminal receptacles) and physiological maturity (i.e., ovary stages) of 208 females captured off the coast of New Hampshire, USA. We found that 27.8% of the females with immature ovaries had sperm in their seminal receptacles, indicating that some females mate while still immature. We proceeded to record the behavior of immature females that were about to molt after placing them in tanks with mature males to determine if mating was consensual. A mature female that is about to molt typically approaches a male in a den, exchanges chemical signals (pheromones) with the male, enters the den to cohabitate with the male, and then molts, mates, and remains with the male while her soft, post-molt, exoskeleton hardens. Previous studies have demonstrated that in order for this sequence of behaviors to take place normally, the exchange of chemical signals is important, and probably necessary. In this study, 11 of 14 immature females exhibited normal mating behavior and successfully mated. It therefore appears that some female lobsters become sexually active before they are physiologically capable of reproducing. Moreover, these females might use "dishonest signals" to trick males into mating to gain protection from them while their exoskeleton hardens.