Lobster: what you don’t know

By John Mark Hanson, Ph.D., Marine Biologist

I recently went on a cruise in the Caribbean and was asked “What do you do for a living?”

I responded that I am a marine biologist who works with lobsters. This puzzled the questioner, who thought lobsters just sort of sat there on the bottom of the ocean and didn’t do much of anything until we caught them. The misconception seemed to be based on the idea that “we see so many lobsters in restaurants that we obviously know everything there is to know about them.” Hardly.

What don’t we know?

Such basic information as the development and structure of male and female reproductive systems are little known, diet is poorly understood, determining a lobster’s age is just beginning to be possible, actual catches are not yet recorded, and reliable estimates of population sizes (independent from catches) do not exist.

Here are some things you may not know about lobster:

• Lobster, like you and me, can be right- or left-handed – or clawed. When larval lobster settle to the bottom, their claws are identical. But within several molts, the claws become specialized. The larger claw, which defines left- versus right-handedness, is the crusher and is “slower.” The narrower claw is the cutter and lobsters can move it quite quickly; they can even catch small fish with it. Lobster also have small claws on the next set of legs, used to tear food into smaller pieces that are then shovelled into the mouth.
• If a lobster loses a claw or a leg, it grows a new one. The new one appears at the next molt. It can take several molts, however, for the claw or leg to attain full size.
• Crabs walk sideways, and those that can, swim backwards. Lobsters walk forward and backward and can swim forward and backward using their swimmerets. When startled, however, lobsters swim quickly backward using strong, repeated tail flips.
• A female lobster’s tail is wider than a male’s to accommodate her eggs. The eggs are extruded in late summer or early autumn, glued to the swimmerets, and carried until early summer the next year. The female, then, molts and mates mid-summer but does not fertilize her eggs until the end of the next year. This means the sperm packets are stored for over one year!
• Lobsters eat whatever they can capture and kill. In rocky areas, they eat large amounts of mussels, crabs and even sea urchins. In sandy or gravel areas, they eat crabs, polychaetes and small sea stars.
• Lobsters cannot molt properly or breed unless they consume substantial amounts of crab. (It does not matter if they are rock crab, Jonah crab or green crab.) However, the critical nutrient in the crab has not been identified. Crab, actually, is a more effective bait than fish, but the large amounts of bait needed each day make fish easier to obtain.
• Lobster often eat their own shell after molting. They also capture and eat other lobsters, especially those that are defenceless during the molt. Despite the risk of cannibalism, very small lobsters are often found in the cracks and crevices around the lairs of very large lobster – presumably scavenging bits of food from the large lobster.
• Until they reach a length of 12 to 15 cm, lobsters spend most of their time in crevices, under rocks, or in burrows. They are referred to as cryptic. They then spend more time out in the open (vagile stages), although they often have a home burrow or cave. Extensive surveys have shown these intermediate-sized lobsters are seldom consumed by fish, in part because large fish such as cod do not live in the warm shallow waters preferred by lobster but also because the lobster are too big to fit into any but the largest cod’s mouth.
• Once lobster become large juveniles or small adults (about 30 cm long – commercial size), they are too large for anything but sharks to eat and are also quite aggressive and will threaten or attack potential predators with their large claws. The main source of mortality for larger lobsters is the fishery, followed by cannibalism.
• Lobsters can live up to 45 or 50 years in the wild, but this is a guess because the ability to assign reliable ages to lobster is still in development. Their longevity may be due to an enzyme that repairs DNA sequences. The largest, and presumably oldest, lobster ever recorded weighed 20 kg, but the largest lobster in existence is the statue in Shediac, New Brunswick, at 11 metres long and weighing 55 tonnes.
• Lobsters have clear blood that turns blue when exposed to air. This is due to the copper in the hemocyanin protein that oxidizies when exposed to air.
• While the popular media reports that there is great fear that the invasive green crab will wipe out lobster populations, nothing could be further from the truth. In highly artificial laboratory conditions, with no hiding places, a large green crab can capture and kill much smaller lobsters. But lobster remains have never been detected in green crab stomachs in the wild. When they are of near equal size, lobster capture and kill the green crab; and lobster larger than the green crab have little difficulty catching and killing them. When confronted by lobster, green crabs typically will threaten and try to attack the lobster, which either ignores or kills and eats the crab. In contrast, native crabs (like the rock crab and Jonah crab) confronted by a lobster flee or try to burrow.
• One last thing you may not know about lobster is that their populations have increased to historically unprecedented numbers because of long-term management efforts.