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The Northern Shrimp

Shrimp fisheries in eastern Canada have shown rapid growth during the last decade and are now ranked fourth in value among shellfish species, behind lobster, scallops and crabs. This growth, especially apparent in northern offshore regions, has been made possible by advances in technology, exploitation of new fishing areas and maintenance of good market prices.

At the same time, older shrimp fisheries in Alaska and the Gulf of Maine have declined due to reductions in abundance.

The northern (or pink) shrimp, Pandalus borealis, is the most commercially important of more than 30 shrimp species found in the Canadian Northwest Atlantic. A closely related species, the striped pink shrimp, Pandalus montagui, at times occurs as a by-catch of varying proportions but, more recently, large concentrations of this species have been found at certain locations in the eastern Hudson Strait and Ungava Bay.

Description

Shrimp belong to a class of animals known as the crustaceans which includes lobsters, crabs, and crayfish. They possess a hard outer shell (exoskeleton), have jointed legs and, since most are aquatic, breath through gills. The northern shrimp is pale scarlet, has a pair of large compound eyes and attains total lengths of 15 to 16 cm. The shell covering the head and thorax (carapace) is modified into a long, curved, satire-like structure called a rostrum which has numerous spines on both edges.

Many shrimp, including the northern shrimp, are good swimmers. Appendages on the tail (abdomen), called pleopods, act like paddles and enable the animals to move with remarkable agility, both horizontally and vertically, over considerable distances. Sudden flexing of the tail also allows rapid movement over short distances as an emergency mechanism of escape.

Distribution

Northern shrimp are found in both the Atlantic and Pacific Oceans. In the northwest Atlantic, they occur as far south as the Gulf of Maine and extend northward to the Davis Strait. Distribution is continuous through east Greenland and the northeast Atlantic, including the Norwegian, Barents and North Seas. In the western Pacific, distribution extends from waters off Japan to the Bering Sea, and in the east from the Aleutian Islands south to the Washington-Oregon coast.

Areas on the Canadian east coast where shrimp are harvested include the Gulf of St. Lawrence, Scotian Shelf, Labrador Channels and Davis Strait. The concentrations of the striped pink shrimp recently found in the eastern Hudson Strait and Ungava Bay have not been harvested on a regular basis, but show economic potential.

Water temperatures where the northern shrimp are most abundant in the northwest Atlantic generally range between 2° and 6°C. In some areas, these temperature requirements restrict their distribution to depths greater than approximately 180 metres. There also is a relationship between size and depth, with larger animals generally occurring in greater proportions in deeper water. These shrimp appear to prefer areas where the bottom is soft and muddy.

Migrations are of two types, horizontal and vertical. Horizontal migration is apparently seasonal and occurs when egg-bearing females migrate to shallower water (within the limits, of course, imposed by temperature), where they are often found in dense concentrations. After eggs hatch, distribution is usually less concentrated. Vertical migration occurs on a daily basis as the shrimp tend to leave the ocean floor at night and move upward in the water column, presumably in search of small pelagic crustaceans which form part of their diet.

Life History

A hermaphrodite is an organism which possesses the reproductive organs of both sexes. Protandry is a hermaphroditic condition in which male sex organs develop and function before the female organs. The northern shrimp is a protandric hermaphrodite which means simply that it first functions sexually as a male, undergoes a brief transitional period, and spends the rest of its life as a female. In some areas, early maturing females are found and in these instances the male phase is suppressed or absent.

In eastern Canadian waters, shrimp eggs are rayed during late summer and fall and remain attached to the abdominal appendages of the female until the following spring. An average-sized female carries around 1,700 eggs. These develop over the egg-bearing (ovigerous) period and hatch as larvae which bear little resemblance to the adults. The larvae float to waters near the surface where they feed on small planktonic organisms. After a few months, they begin to spend more time nearer the ocean bottom and begin to look more like the adults.

Most shrimp remain immature through the second year and mature as males in the third. Generally, the transition to the female stage takes place early in the fourth year, followed by ripening of the ovaries, mating and spawning. Females may spawn in one or more successive years and live to be five years of age and older. In areas where water temperatures are at the lower end of the range of tolerance, both growth and maturation are retarded while the life span tends to be longer.

Shrimp, in order to grow, must periodically shed the hard outer shell through a process called moulting (ecdysis). When the shrimp crawls out of the old shell, its body begins to absorb water and increase in size before the new soft shell begins to harden. During the period when the shell is soft, the shrimp are highly vulnerable to predators. Actual growth takes place during the period between moults (intermoult) as the water previously absorbed is replaced by body tissue. Moulting and growth slows down as the shrimp become older. Females can grow only when they are not carrying eggs.

Northern shrimp feed on the bottom during the daytime on various items such as worms, small crustacea, detritus and marine plants. Small pelagic crustacea called copepods and euphasids (krill) are probably heavily preyed upon at night when the shrimp migrate vertically in the water column.

Shrimp themselves serve as food for many species of fish, especially Greenland halibut (turbot) and cod. They also have been found in the stomachs of harp seals.

The Fishery

Shrimp fisheries in the Gulf of St. Lawrence began in the mid 1960s in the Sept-Iles, Quebec area. Fisheries have since developed on the west coast of Newfoundland in the late 1960s and early 1970s, and in an area north of Anticosti Island during the mid 1970s. In 1977, New Brunswick vessels participated in a relatively small fishery on the Scotian Shelf and large trawlers fished newly discovered shrimp concentrations in Hopedale and Cartwright Channels off the Labrador coast. The larger vessels extended their effort for shrimp into the Davis Strait area in 1979, and in 1980 a limited amount of fishing for the striped pink shrimp was conducted in the eastern Hudson Strait and Ungava Bay.

Vessels participating in these fisheries use small meshed otter trawls to catch the shrimp. Both net and vessel size vary, depending on the fishery. Small stern trawlers (less than 20 m) are used on the west coast of Newfoundland for trips of one or two days' duration, while vessels from Quebec and New Brunswick generally are larger, capable of towing larger trawls and able to remain at sea for longer periods of time. The larger offshore stern trawlers in the Labrador Sea and Davis Strait use very large trawls and can remain at sea for a month or more. The small meshed trawls often catch groundfish which sometimes are utilized to supplement the shrimp catch.

Landings of northern shrimp on the east coast of Canada increased from less than 2,000 metric tons (t) in the early 1970s to around 15,000 t in the period 1979-81. The product is landed in a number of forms. Fresh and freshfrozen whole shrimp often are returned to shore for cooking and peeling. Some of the larger offshore trawlers have cooking and peeling machinery onboard and deliver a very advanced product. Therefore, the landed value of shrimp is variable and difficult to quantify. In 1979, however, it was estimated that the landed value of shrimp on the Atlantic-coast-of Canada was around $13 million.

The northern shrimp resources of Sept-lles, Quebec and Port au Choix, on the west coast of Newfoundland are now being fully utilized. Areas in the southern Gulf of St. Lawrence around Anticosti Island and on the Scotian Shelf are becoming increasingly important as the industry expands. Shrimp stocks off Labrador and in the Davis Strait are fully exploited where catch rates prove economical. The fishery potential for the striped pink shrimp resources in Ungava Bay and eastern Hudson Strait has not yet been demonstrated.

Research and Resource Management

The northern shrimp resources are monitored through research surveys and sampling of the commercial catch. Catch rates of shrimp and fish species are recorded, and detailed observations are made on shrimp size distribution, sex, maturity and egg production. These data provide useful information on the distribution and abundance of the resource, the effects of fishing and changes in the environment, and potential for the fishery in the near future.

Present research is directed towards age determination, estimation of mortality rates, effects of environmental parameters (e.g., temperature, currents) and relationship with major predators, especially Greenland halibut and cod.

Based on information from research and observation of the fisheries, estimates of yield (which can hopefully be maintained for some years) have been obtained. Total allowable catches have been revised accordingly for most areas off Labrador and in the Davis Strait. The number of participants in these fisheries also has been limited and a mesh size regulation to permit the escape of smaller, less marketable, shrimp has been enforced in northern areas. Fisheries in and around the Gulf of St. Lawrence also have been controlled by limited entry, primarily based on acceptable economical returns for all participants.

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Last updated: 2006-06-06

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