Selected Shrimps of British Columbia
His name was Hermaphroditus- son of Greek gods who according to mythology became united in a single body with a beautiful nymph. Thus, he gave his name to an unusual phenomenon in which a single organism has both male and female characteristics.
It is a peculiarity of nature amply demonstrated by the six shrimp species that thrive off the coast of British Columbia. Their strange habit of changing sex in mid-life, spending a year or two as active males before being transformed into females, is known as protandric hermaphrodism. In fact, although most individuals follow this pattern, in some species a more or less large proportion of shrimp actually bypass the male phase.
The six varieties of shrimp - all belonging to the family Pandalidae- occur in sufficient numbers to support several small commercial and recreational fisheries. The shrimps are generally similar in appearance and size. However, there are a number of minor distinguishing anatomical features and unique colour patterns which have inspired some of the common names used by West Coast shrimp fishermen and allow identification of the varying species.
Mature shrimps breed in the late autumn or early winter. A short time later, developing eggs appear on the female's swimmerets-a fringe of short appendages on a shrimp's abdomen. They are carried there until hatching in the spring.
After leaving the female, the shrimp larvae swim freely for about three months before settling to the bottom. Larvae may inhabit the entire water column or be restricted to the lower half, but there is a trend to inhabit increased depths prior to settlement.
Shrimps mature initially as males in the first year (at about six months), or in the second year (at 18 months). Then they spend one or two seasons as sexually active males. Afterwards, changes occur which turn these adult males into females. They usually survive one or two years in that form.
Sidestripe or Giant Shrimp (Pandalopsis dispar)
In size, the sidestripe is second only to the prawn, with large females reaching 20 cm in length. The long antennules and striped abdomen clearly distinguish this shrimp from other species.
The sidestripe occurs in the northeastern Pacific Ocean from the Bering Sea to the Oregon coast. In British Columbia, it is caught by trawl in English Bay, Howe Sound, Stuart Channel, Barkley Sound and Chatham Sound, but it rarely enters baited traps. It is generally found on muddy bottoms, at depths of 90 to 201 m.
Maturity as a male is attained during this shrimp's second year. Sex change occurs in the third year, with relatively few females appearing to survive into the fourth year. In the Strait of Georgia, females carry eggs from October to March.
Pink Shrimp (Pandalus borealis)
The length of this shrimp is normally 7.5 to 10 cm, but larger individuals may reach as much as 15 cm. The pink shrimp and the smooth pink are similar in colouration, with both species lacking bands or blotches on the legs. The main distinguishing feature of the pink is the sharp spine or lobe that points backwards from the curve of the abdomen.
The pink shrimp is a wide-ranging species, known in the Chukchi and Bering seas, from Unalaska in the Aleutian Islands to the Columbia River mouth, along the Asian coast from Kamchatka to Korea, from the Barents to the North Sea, and from western Greenland to the Gulf of Maine. In British Columbia, it occurs chiefly in mainland inlets, probably because water temperatures tend to be lower there. Trawl catches of the species are made on mud bottoms at 54 to 90 m in Burrard Inlet, Howe Sound, and Chatham Sound.
The pink is an active male in the second year and becomes a female during the third year. It lives at least three years. In Burrard Inlet, about half the individuals in an age group may mature exclusively as females. The eggbearing period lasts from November to April.
Prawn or Spot Shrimp (Pandalus platyceros)
This species is the largest of the local shrimps with large females exceeding 23 cm in total length. Its body colour is usually reddish brown or tan, with white horizontal bars on the carapace, and distinctive white spots on the first and fifth abdominal segments.
At times, juveniles have been observed on muddy bottoms, but adults normally live in rocky crevices and under boulders. The prawn ranges throughout the northern Pacific from Unalaska to San Diego, California, and from the Sea of Japan to Korea Strait. Commercial trap fishing is carried on all along the British Columbia coast. Although the fact is not obvious from statistical records, the prawn now ranks first in landed value in the shrimp fishery. The most popular sport trapping grounds are located in the Strait of Georgia and in southern mainland inlets.
The prawn is a male during its second and third years, then changes sex in the third or fourth year. Eggs are found on females from October to March.
Humphack or King Shrimp (Pandalus hypsinotus)
The humpback ordinarily is 10 to 12.5 cm in length, but large
females may reach
17.5 cm. This shrimp is called humpback because of the arched shape of the carapace. The conspicuous mottling on the abdomen is also distinctive.
The humpback occurs in the Bering Sea, from the Aleutian Islands to Puget Sound, and in the Ohkotsk Sea as far south as the Korea Strait. In terms of the shrimp fishery, it is of minor importance, appearing in trawl catches along with pink shrimps in Burrard Inlet and Stuart Channel, and as the main by catch from prawn trapping in central and northern mainland inlets. However, it is held to be the finest eating shrimp of all six species.
This species attains maturity as a male, and in varying proportions as a female, in the second year, and becomes a female during the third year. Subsequent survival into the fourth year is very low. Female shrimps carry eggs from November to April.
Smooth Pink or Ocean Pink Shrimp (Pandalus jordani)
The smooth pink shrimp is very similar in size, colour, and body characteristics to the pink shrimp, but it lacks that prominent spine or lobe on the curve of the abdomen.
The recorded distribution of this species ranges from Unalaska to near San Diego, but exploitable populations occur only between Queen Charlotte Sound and northern California. Local trawling grounds lie along the continental shelf off Tofino and Nootka Sound, in Barkley Sound, and along the east coast of Vancouver Island. This shrimp, now in second place commercially, was the most valuable shrimp species landed from 1960 to 1978.
Maturation as a male occurs during the second year, with sex change taking place in the following year. In the Strait of Georgia, it is known that as many as 40 per cent of an age group may mature first as females. The egg-bearing period extends from November to April.
Coonstripe or Dock Shrimp (Pandalus danae)
A female coonstripe shrimp may reach a total length of 14 cm but the usual length is 7.5 to 10 cm. The irregular striping of brown and red on the abdomen gave rise to the one common name; the other followed from this shrimp's habit of living at times around docks. Otherwise, it inhabits sand or gravel bottoms, usually where a rapid tidal current flows.
The coonstripe ranges from Sitka, Alaska, to near San Diego, and a continuing productive trap fishery is carried out in Sooke Harbour. Through the nights of late summer and early fall near Sidney and elsewhere around the Saanich Peninsula, sportsmen pursue the coonstripe with baited ring traps and dip nets.
Shrimps of this species function as males during the first and second years, and as females in their second and third years. Some individuals mature first as females never functioning as males. Females with eggs may be found year round, but the main season is from November to April.
Fishing Methods and Areas
The Trawl Net
All six shrimp species are fished from shallow to moderate depths ranging from 27 to 201 m. Those species generally found on muddy or sandy bottoms are fished with a bag-shaped net or trawl. The trawl net is conical, open at the mouth and tapering to an apex at the other end. As the net is towed along the bottom, shrimps are gathered into the mouth of the net, thus passing into the apex, or cod end.
In order to function effectively, the mouth of the net must remain open. A length of tubular aluminum (up to 12 m long) or, less frequently, a spruce pole, achieves this purpose on the beam trawl. In the otter trawl, the upper edge of the net mouth is supported by glass or aluminum floats, and the sides (or wings) of the net are attached to two vaneshaped boards. When the gear is towed along the bottom, water resistance causes the boards to spread open the net mouth. Mesh size of shrimp nets ranges from 2.8 to 3.8 cm, depending on the net material.
The smaller, one-man shrimp beam trawlers (about 11 m long) are usually converted salmon gillnetters that use the net drum as a trawl winch. Shrimp beam trawls are towed slowly (about 1 1/2 nautical miles per hour). That low speed prevents too large a fish by-catch and gives a catch that is reasonably free of mud. The tow may last one or two hours, depending on the nature of the fishing ground and the availability of shrimps.
The trawl is hauled in slowly. When the net mouth reaches the surface, the beam is detached and allowed to float alongside the boat. After dousing the cod end to clear the catch of any mud, the fisherman pulls the net aboard.
Larger shrimp boats (12 to 25 m long) use the otter trawl-a gear normally handled by two or three people. They trawl on grounds in the Strait of Georgia and Chatham Sound, as well as along open coastal areas. Shrimp otter trawls are towed at 2 to 2 1/2 nautical miles per hour so they catch more fish -cod, pollock and dogfish-cod, pollock and dogfish-than do the beam trawls. When the gear is hauled in, the otter boards and net are taken aboard, the latter being wound on a drum until the cod end is reached. This heavy load is then lifted by means of an overhead boom.
All shrimps, except the sidestripe, will readily enter baited traps, but only the prawn and coonstripe shrimp at present are target species for trap harvesting.
Prawn traps vary in shape and size. One type is oblong, about 60 x 30 x 30 cm, with the sides covered with shrimp netting, plywood, or plastic. Another, the Pardiac trap, is cylindrical, about 56 x 28 cm, and is covered with netting. At the end of each trap, or at two or three places around the perimeter, are funnel-shaped openings. In the fishing operation, traps are baited and laid out along a bottom line, with the position of the traps shown by surface buoys. Most prawn trapping is carried out at between 18 and 90 m. Coonstripe shrimps in Sooke Harbour are fished in the same way at depths not exceeding 40 m, but in this case each trap has its own line and buoy.
Many fishermen sell their catches, especially prawn and sidestripe shrimps, right off the boat and much of the catch is destined for local consumption. However, most of the smaller shrimp species are marketed through a registered processing plant, where the product is cooked and peeled and sold as frozen, fresh or canned cocktail shrimp. The larger shrimp is generally sold whole, or headed, as a fresh or frozen product. Some of the product is sold through these registered plants for distribution to local and foreign markets.