Commercial Fisheries News - March 2002

Part II: More males than females

What happens when there are more lobsters of one sex than the other confined in a small area?In the February CFN, we looked at the phenomenon of “serial monogamy ” that I observed in a controlled situation where female lobsters outnumbered males.

Now let ’s look at what happened when the situation was reversed.

To recap,I stocked four 3,000 gallon aquariums with different ratios of male to female lobsters and found that varying the sex ratio had a dramatic effect on courtship and the timing of female molting and mating.

Slanting the sex ratio toward males in the tanks resulted in utter chaos.Initially, four males and two females were introduced into each aquarium.The aggression was so intense that one male was removed from each tank after two days.

No male established dominance and no male completed the experiment with all of his legs.

Although all of the males lived,one male had no legs by the end of the season. Another male attempted to mate with a hard-shelled female by dragging her into his shelter,mounting,and trying to turn her over,but each time she escaped.

Whereas all of the females molted when there was a dominant male,only half of the females molted in this situation.They apparently couldn’t decide which male to pair with and moved in and out of up to three male shelters per day.

When five females were housed in the absence of males,they simply put off molting.Only four out of 20 females molted.Although none of the females were killed,all sustained serious injuries — including loss of claws or legs — when they molted.

These results raise intriguing questions regarding social control of molting.They also indicate that sex ratio is important to the lobster mating system.The most successful reproduction and fewest injuries occurred when one male was able to establish dominance and control a mating shelter.

In nature,lobsters have far more space to occupy.Are sex ratios skewed in certain locations at certain times of year? Do males set up mating territories like the ones established in the aquariums? These are clearly questions worthy of further study.

Ask the Lobster Doc