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The American Lobster Underwater World 2 QL 626 U5313 no.18 c.2 - The American Lobster Underwater World 2 Who hasn't looked at a lobster in a fîsh or scampi. The lobster belongs to the store and wondered how such an ugly decapod or 10-legged family of crustaceans The American creature could be the epicurean's delight? which includes shrimps, prawns, crabs and At one time surplus catches of lobster crayfish. Lobs ter were used as fertilizer. Fishermen con- Lobsters have a jointed external shell, sidered them a nuisance when they became which protects and supports the body parts, entangled in their nets. while still permitting movement. The However, for qui te a number of years, lobster's body is formed mainly by the the lobster has become a highly sought after cephalothorax, or head and chest area, and creature. Gourmets the world over prize the six-jointed abdomen which is common- this crustacean as the most delectable. ly known as the tail. The claws, carried on As a result, lobsters are now trapped its first pair of legs and to which it owes unremittingly, and it appears that their much of its distinctiveness, are called the populations - at least in certain areas - pincer and the crusher according to their are threatened. Most females don't get a respective functions. Four pairs of walking chance to reproduce even once before being legs occur on its thorax, and a series of caught by the fîshing industry. swimmerets, used for carrying eggs in the Scientists are concerned, and are calling case of the female, are suspended from for stiffer contrais. Fishermen and pro- beneath the abdomen. Lobsters corne in ducers claim that the industry is already various colours - mostly colours which are severely over-regulated. In any event, there useful for camouflage purposes, but are is a need for reexamination of a manage- usually greenish when in the water, tending ment code which has evolved over the past to redden when out. 90 years. Skillful management must weigh Adult lobsters vary greatly in size among potential short-term lasses against long- localities, depending upon the age and local term gains. Ultimately, it is obvious that all growth rate, as well as the intensity of the concerns are contingent upon the protec- fîshery . In areas where the exploitation rate tion of the species. is high, the local stock of lobsters is main- tained at a young average age. The average Description size is consequently smaller than it would be That most coveted of crustaceans, the if there were less fîshing pressure. The American lobster (or Homarus americanus intensively-fîshed Gulf of St. Lawrence as it is known scientifîcally), is an in- stocks have an average size of less than vertebrate crustacean. It has no immediate 400 g. Sorne lobsters can grow to a size of relatives in Canada. lt does have, however, more than 20 kg if they survive the fîshery one European brother Homarus and natural mortality. vulgaris. Also related is the Norway lobster Distribution Lobsters live along the east coast of North America from North Carolina to Labrador. They are abundant off Maine, southwest Nova Scotia, and the Gulf of St. Lawrence coastline of the Maritimes. Lobsters prefer a habitat where they can find shelter. In deep water canyons off the coast of the U .S., lobsters have been observed lodged individually in small bur- rows dug into the face of clay cliffs. Inshore lobster populations are found on rocky bot- toms, where a large number of individuals can obtain appropriate shelter. On sand or mud, lobsters may be found hiding under rocks of about their own size. In a number of areas lobsters tend to be larger in deeper water. There are excep- tions. For example, large egg-bearing females are found in shallow waters in the Bay of Fundy where they reproduce and moult during the summer months. Just as the emergence of droves of office workers on a sunny day in spring does not necessarily indicate that the number of of- fice workers themselves is on the rise - soit is with lobsters. They become more active Underwater World 3 when the water begins to warm up. Thus soon after moulting, concentrating on high the catch increases and it appears that there calcium foods to encourage the rapid are more. ln fact, they are only more active. hardening of its shell. The calcium which So water temperatures, if not taken into ac- had been stored in the stomach walls is also count, can play havoc with demographic used at this time. Sometimes it may even eat surveys. its old shell. For one or two months after a moult the lobster's flesh is watery and does Life History not quite fit the shell. During this period its The Iobster begins its life as an egg, glued appetite is enormous and it is readily at- to the swirnmerets on the underside of the tracted to the bait in lobster traps. female's abdomen. The speed of matura- Growth slows down progressively as the tion at this stage may be accelerated by juvenile Iobster grows to adulthood. Since warmer water temperatures. Usually the lobsters grow faster in more temperate eggs hatch in the summer, and the newly- waters they may moult more often. In the released Iarvae float to the surface where Northumberland Strait, for example, where they feed upon smaller planktonic summer water temperatures may reach organisms and undergo three moults, each 20°C, a lobster at the current canner time growing larger, and more similar to an minimum of 63.5 mm carapace length, can adult. In three to six weeks, depending on moult twice in one year. Once a lobster has the temperature, the juvenile lobster replenished the flesh within its new shell, it descends to the sea bottom. At this stage its will be about 50 per cent heavier than total length is about 15 mm. The mortality before a moult. So in one year a lobster rate of larvae is very high, and only about from the Northumberland Strait would one per cent of the floating larvae may set- grow from 200 g to 450 g, and would moult tle on the ocean floor. twice, whereas his counterpart in a cooler Luckily, each female produces enormous habitat would average 300 g, and moult on- numbers of eggs. For example, a large ly once. "canner" with a carapace or shell length of Temperature is also a factor in the age at 78 mm releases about 7 ,500 eggs at one which a lobster attains sexual maturity. time. Even if only one per cent of these Female lobsters in the Northumberland make it to the bottom, this still means that Strait may mature at 200 g or three years of Fig. J. Egg-bearing or berried lobs ter. each female has produced at least 75 off- age, whereas their counterparts in the Bay spring that have survived. Typical large of Fundy will not mature sexually until they breeders in the Bay of Fundy release 30,000 are 700 g or eight years of age. eggs at a time, and the jumbos of more than The size at which the average female is 125 mm in length have been known to pro- mature and capable of producing eggs to duce more than 40,000 eggs. replenish the population is very important ln order to survive, small lobsters Iead a in the regulation of the fisheries harvest, Fig. 2. C/ose-upsection ofberried lobster. very secretive existence, so most of their because if females are not given the chance time is spent hiding in burrows. Through- to contribute to the reproduction of the out their lives, they prey upon correspond- species, the lobster population will obvious- ingly small individuals of high food quality, ly suffer a decline. This is the main problem such as crabs, mussels, clams, sea urchins facing the lobster population today. and starfish. There is no evidence of canna- balism in the wild. Reproduction As the growing lobster becomes too big The female is only sexually receptive for a for its shell, it sheds it for a larger one. Be- few days after moulting, while her shell is tween moults, the flesh becomes pro- still soft and flexible. When lobsters mate, gressively more densely packed inside the the male deposits sperm in the spermatheca shell. Meanwhile, a new soft shell develops between the female's last two pairs of walk- inside the old one. Calcium salts are absorb- ing legs. The sperm is then stored for as ed from the outer shell and stored in the long as a year, until the eggs are ready. At stomach wall. The lobster arches its body that time the eggs are released from the into a "V" form, folded at the junction of openings of the oviduct at the bases of the carapace and abdomen. The large flexible third pair of walking legs. As they pass old membrane stretches, then splits, and the toward the swimmerets, sperm is released to animal lies on its side and backs out of the fertilize them. The eggs are then carried on shell. Once free, the lobster flips back into the swimmerets until the following year. In the normal position and proceeds to suck in the past it was assumed that after hatching water and to puff itself up to about IO to the eggs, the female would moult and then 15 percent larger than its previous size. mate again to recommence a two-year At this stage the lobster's shell is very reproductive cycle. However, it seems that tender and the Iobster is extremely very large females are able to conserve vulnerable to predation.
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