Pollock Ing Pollock, One of Canada's Important Juveniles, As the Adult Colouration Commercial Fish of the North Atlantic
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QL 626 Scientific Excellence • Resource Protection & Conservation • Benefits for Canadians U5313 no.35 DFO - Library I MPO - Bibliothèque 1993 c.2 --12064680 - Underwater World 2 f you buy Boston Bluefish in your sides and fins . This is simply an adap- I local supermarket, you'll be purchas- tation to living in shallow areas as Pollock ing pollock, one of Canada's important juveniles, as the adult colouration commercial fish of the north Atlantic. returns when these fish move offshore. Pollock (Pollachius virens L.), a mem- The lateral line stretches from the end ber of the Gadidae, or "cod" family, is of the gills to the caudal fin and is white also known as saithe, coalfish, and or pale grey. The body is deep, with green cod. lt can be found in northern white firm flesh. While considered a waters on both sides of the Atlantic - member of the cod family, the pollock from southern Newfoundland to New can be distinguished easily from the cod Jersey on the North American side, and and haddock by its distinctive forked from West Greenland to Northwest tail, green colour, pointed snout and Europe to the Bay of Biscay on the projecting lower jaw with a much European side. reduced, if not absent, chin barbe!. Pollock are voracious eaters, and The life span of pollock is approxi- since they often congregate in large mately 17 years. During this time they numbers, they can have a severe impact can grow up to 1.5 metres in length, and on schools of herring, juvenile cod, had- from 8 to 21 kilograms in weight. The dock and hake. They are used largely for largest pollock ever recorded weighed human consumption. 21.1 kg, and was taken off New Jersey Although generally referred to as by John T. Holton. Located as they are groundfish, pollock are really bentho- on both sides of the Atlantic, pollock pelagic as they are found throughout the nevertheless seem to exhibit similar water column, feeding on smaller fish characteristics at either location. For and crustaceans near the bottom and instance, both North American and actually surface-feeding on squid, European pollock are cold-water fish, shrimp, and shrimp-like euphausiids. preferring temperatures between 0° and 10°C, although maturation of sex Description organs and incubation of eggs require The pollock, like its close relatives, water temperatures in the upper part of the cod and haddock, has three dorsal this range. fins and two anal fins (Fig. 1). lt is generally green, varying from deep olive Reproduction to brownish green on the back, blending In the northwestern Atlantic pollock into a pale yellow or grey on the sides are late fall, early winter spawners. below the lateral line, and then into Breeding generally begins in late Octo- silvery grey or white on the lower sur- ber when water temperatures have cool- face . Young fish often can be found ed to 8 to 10°C, with peak activity with a definite red or orange hue on the occurring from November to February when the water reaches 5°C to 6°C. In Figure 1 European waters of the eastern Atlan- An adult pol/ock (Pollachius virens L) tic, spawning does not occur until January, when temperatures rise to 7°C; it then continues into April. Spawning occurs in water that ranges from 15 to 50 fathoms. Underwater World 3 While the average female produces Gulf of Maine for their first three years. about 200,000 eggs, there have been They then begin to move offshore into recorded cases of large females with the fishery where they mature at age five more than four million eggs. The eggs years and older, when the life cycle have a diameter of approximately l mm; begins again. A similar behavioural they are buoyant and drift near the pattern is exhibited in European waters. surface. Incubation time is from seven More recent information suggests that to nine days, depending on water tem- pollock show a strong homing tendency, perature. When the larvae hatch, they as they have been traced back to the are 3.5 to 4 mm in Jength and have a same inshore location in subsequent large yolk sac attached which provides years. nourishment for the first five days. At the end of that period, the yolk sac has Management and Migration been absorbed, and the larvae continue Pollock are abundant from the Gulf developing until they reach a length of of Maine to the northern end of the 25 to 30 mm, at which time they exhibit Scotian Shelf. Until recently, however, most of their adult characteristics. The very little has been known about their annual rate of growth is fairly rapid migration routes and distribution, other during the early stages, up to 12.5 or than the fact that Jeffries Ledge in the 15 cm per year for the first three years Gulf of Maine was the only known of development; 5 to 10 cm per year for spawning ground. Therefore, it was the next three years; and slowing down assumed that ail the fish along the to 2.5 to 5 cm per year as the fish reach Scotian Shelf and Bay of Fundy migrat- sexual maturity at five years. ed down to the Gulf of Maine to spawn Larvae begin to migrate inshore to and then moved back up along the nursery areas almost immediately. Here coast. For Jack of better information, they are known as " harbour pollock" the species was therefore managed as and can be found ail along the coast of one stock. Several studies were conduct- Nova Scotia, New Brunswick, and the ed in the early part of the l 960s using Figure 2 tag and recapture methods to establish Tagging gun, tags and reward poster for pol- migration patterns and spawning lock used in the tagging program run by DFO. grounds. The results indicated that other spawning areas probably existed along the Scotian Shelf but not enough data POLLOCK were collected to provide adequate proof. RE WARD In 1978, the Department of Fisheries and Oceans (DFO) began a juvenile tag- SPECIAL GROUNDFISH TAGGING STUDY and-recapture program from various $3 for tag only $5 for tag and ftsh sites along the Scotian Shelf and Bay of Fundy to try to assess pollock migration 8 patterns and spawning areas (Fig. 2). To date, approximately 38,000 pollock have been tagged in this experiment. Prelimi- nary results show these juveniles dis- ' perse ail over the Scotian Shelf and DA TE, PLACE, FORK LENGTH, AND METHuu OF CAPTURE 17 SEND OR GIVE INFORMATION, TAG AND/OR THE FISH TO: 19 Sampling Technician Marine Fish Division Marine Fish Division OR OR Bedford lnstitute OR Biological Station Fisheries Officer PO Box 1006 St. Andrews, NB OR Dartmouth, N S. B2Y 4A2 E0G 2X0 Community Services Ph 902 426 -8390 Ph 506 529-8854 Officer Underwater World 4 northeast peak of Georges Bank, with The Fishery only one recapture, to date, from the Pollock off the Canadian and Amer- Jeffries Ledge area (Fig. 3). ican coasts were first brought under Parallel to these experiments, other quota management in 1973. Since that scientists with DFO have been looking time, when pollock were generally taken at the distribution of eggs and larvae in a bycatch fishery, catches have risen from ichthyoplankton research cruises. steadily to a maximum in 1981 of 58,000 These cruises show concentrations of metric tons for essentially a directed eggs and larvae at several areas along the fishery (Fig. 4). Canadian and Ameri- Scotian Shelf, Browns Bank, northeast can fishing fleets have traditionally been Georges Bank, and Jeffries Ledge responsible for the majority of these during established spawning times. A catches, with Foreign fleets contributing short incubation period, in addition to from IO per cent in 1975 to Jess than the fact that there is little proof for large 1 per cent in 1981. Although pollock are scale drifting of eggs and larvae, indi- fished ail year long, data suggest that in cate that pollock are spawning in each both North American and European of these areas. waters peak fishing times occur in mid- While it would seem that these prelim- winter and summer. inary results point to the existence of Pollock are fished inshore as well as more than one spawning area and hence offshore. In the early 1900s, the inshore one stock, a great deal is left to be done. fleet used gillnets, hand-lines and long- Modern experiments to determine the lines, and occasionally seines when genetic structure and population of the schools of pollock could be seen near the species are being carried out, and it is surface. Otter trawls accounted for only hoped that they will provide a better a fraction of the catch. While the in- understanding of the population struc- shore fishery is much the same as it was, ture of pollock and hence the answers otter trawlers in the offshore fleet now necessary for good stock management. are supplying the vast majority of pol- lock catches. In 1981, for example, off- shore trawlers took approximately 70 Figure 3 percent of the total pollock catch. It is Distribution of tagging sites and recoveries. also interesting to note that pollock are a good sport fish and many have been taken by anglers using anything from a fly, to a Jure, to a hook and live bait during their spring and fall migrations. 47°N Commercially, pollock is marketed as a food fish. Although found in many ' forms, it is chiefly dried and salted. Fresh or frozen fillets usually are sold 46°N \ as Boston Bluefish, or ''deep-sea ' fi Ilets''.