In England and Wales more fish is landed by trawlers than by all other methods of fishing combined. Trawl-caught fish—soles, plaice, turbot, halibut, cod—are much more valuable than fish caught by drift nets, e.g. herring and mackerel. In England and Wales, in 1913, the weight of pelagic fish caught amounted to 389,262 tons, and of demersal fish 418,038 tons. Although the quantity of the demersal fish was, therefore, only little larger than of the pelagic fish, its value was £7,463,003, compared with £2,531,979, the value of the pelagic fish.
CHAPTER VII
SHELLFISH
Shellfish are divided into two classes: Crustacea, including the lobster, crab, shrimp, prawn, and mollusca, including the oyster, mussel, cockle and periwinkle. Shellfish generally abound in comparatively shallow water near the shore.
Perhaps the most important members of the crustacea are the various minute, pelagic copepoda, of which incalculable myriads form an important constituent of the plankton in all seas. These copepoda live upon the diatoms and other microscopic, marine vegetable life floating at the surface of the sea. The most important edible members of the crustacea are the lobster and the shrimp.
The lobster is found along the coasts of the North Atlantic and Mediterranean, particularly along the European coasts from Norway to the Mediterranean, and off North America from Labrador to Cape Hatteras, The lobster lives in shallow water at about 12 fathoms depth, and frequents a rocky bottom. The lobster’s eggs remain attached to the female until the larvae hatch out. From 10,000 to 12,000 eggs are carried in this way by a female lobster. She protects them from the ravages of fish that will otherwise consume them as food, and by keeping them constantly irrigated with fresh sea-water she promotes their healthy life and development. The eggs may take as long as twelve months to hatch, and although “berried” lobsters are seen in greatest numbers in the spring they are also captured at all seasons of the year.
When hatched the young lobster larvae leave their mother and float up to the surface water, where they develop for a time among the plankton. During the larval period the lobster is a free and active swimmer.
The young larvae are consumed in large quantities by fish such as herring, mackerel and sprat, especially during the summer months when they are most abundant. While developing into a complete lobster it passes through at least three distinct changes of form. When the larva has attained the length of about 3/5 in. it already possesses many of the characteristic features of the adult. Soon afterwards, it sinks to the sea bottom and gradually grows into a complete adult. During the growth of the lobster it frequently casts its shell and grows a new one. Growth only takes place when the shell is cast and while the new shell is hardening. During the first few weeks of its life the lobster casts its shell about once a week, but this casting happens less and less frequently as the lobster grows older. The new shell is formed beneath the old one, and although at first quite soft rapidly hardens when the old one has been cast off. Most adult lobsters cast their shells in July, August and September.