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The Witch Flounder

Although a large proportion of witch flounder is taken as a by-catch of other fisheries, it forms an important component of the Canadian Atlantic groundfish resource.

There was heavy exploitation of witch flounder by foreign ships in the early 1970s, but with the introduction of Canada's 200-mile limit in 1977, foreign fishing for the species was reduced and Canada's take increased.

Description

Witch flounder (Glyptocephalus cynoglossus) or "greysole", as it is also commonly known, is a flatfish like American plaice, yellowtail flounder and Greenland halibut. It lies on its left side with the stomach and other visceral contents on the right.

This species has several characteristics which make it easily distinguishable from other flatfishes. The body is relatively narrow compared to other flatfishes, with a very small head. On the blind side of the head are about a dozen large open mucous pits which are very noticeable. Its body is oval and very thin with the head occupying only about one fifth of the total body length. It has a very small mouth not unlike that of the yellowtail flounder. The body is covered by smooth scales which make it very slippery and extremely difficult to hold.

The body colour of witch flounder is less variable than most other flatfishes, with the eyed side a dark greyish brown and the under side white with minute dark points all over it, giving it a light grey appearance. It can grow as large as 78 cm in length, with a weight of 3.5 - 4.0 kg, although witch flounder beyond 60 cm in length and 2.5 kg in weight are uncommon.

Distribution

Witch flounder reach their northern limits in the Northwest Atlantic at the Hamilton Inlet Bank area (54°N) and have been reported as far south as Cape Lookout, North Carolina. They prefer living in gullies where the bottom is usually of clay, muddy sand or pure mud rather than the hard tops of the banks and inshore ground. In summer they usually move up onto the soft mud and in winter move down into the deeper gullies. Witch flounder have been caught in a bottom temperature range of -1° to 11°C. However, evidence from scientific investigations indicates that they are most abundant within a bottom temperature range of 2 to 6°C.

They are generally a deepwater species and have been caught as deep as 1,441 m off Chesapeake Bay, 1,100 m off North Carolina and 1,569 m off southern Nova Scotia. According to research vessel catches and commercial trawler records, however, the depth of highest abundance of witch flounder in Canadian waters is between 185 and 400 m. The reason for this wide variation in depths is that colder waters in upper water layers in certain areas at certain times generally force these fish deeper until they find suitable temperature conditions conducive to their survival.

Witch flounder are associated with deep holes and channels between the coastal banks and along the deep edges of the banks where water temperatures are usually in a range suitable for their habitation. These localized areas of high abundance are habitually more prominent in the winter-spring time when this species forms rather dense prespawning concentrations. In the eastern Newfoundland area they are most plentiful in the Hawke Channel, Funk Island Deep and the deep channels running into White Bay, Notre Dame Bay, Bonavista Bay and Trinity Bay, with moderate numbers found along the northern edge of the Grand Banks. Witch flounder are not normally found on the shallower parts of the Grand Banks where bottom water temperatures are less than 1°C. However, fair concentrations occur along the deep muddy southwest slope of the Grand Banks as well as the southern slopes of St. Pierre Bank and Burgeo Bank, with small local stocks located both in Fortune and Hermitage Bays.

In most areas on the Scotian Shelf, localized areas of high abundance occur along the edge of the Laurentian Channel, between Sable Island and Banquereau Bank, in the deep holes of Banquereau and at the mouth of the Bay of Fundy. The species is found throughout the Gulf of St. Lawrence, usually in the deeper waters of Laurentian and Esquiman Channels. In wintertime a dense concentration may be found in the channel southwest of St. George's Bay. In summertime they are plentiful on the smooth muddy bottom on the southwest side of St. George's Bay. In the southern Gulf of St. Lawrence, they assemble in the area northeast of Prince Edward Island and just west of Cape Breton Island.

Witch flounder are a rather sedentary species and do not appear to undertake long-distance migrations. They concentrate in selected water suitable for spawning, then disperse in the surrounding areas for feeding. A significant aspect of this species is that they appear to have a "built-in" conservation mechanism for the first several years of life. Young witch flounder are either pelagic (midwater) or they live in very deepwater areas where the only probable threat to them is the redfish fishery. The very rough grounds and great depths where many occur are particularly efficient safeguards against exploitation by existing trawling capabilities. The deepwater phase of the very young also reduces direct competition for food from such groundfish species as the Atlantic cod and the American plaice.

Food

Due to the very small mouth of the witch flounder, the type of food it can eat is obviously restricted to very small animals. The main food item is marine worms of many varieties. They also eat small crustaceans or shellfish similar in shape to shrimp, though by volume, much less than marine worms. Small pieces of dam shell are also commonly found in witch stomachs, with some small fish found on occasion in the very large witch.

Spawning

The spawning season of witch flounder is rather extensive throughout the Northwest Atlantic and occurs in late spring to late summer, depending upon the geographical area of the spawning grounds. Spawning usually takes place in very deep water where temperature conditions are rather high, with the spawning period being less extensive in the north than in the south. The spawning period in the southern Labrador-northeast Newfoundland Shelf area continues from March to July, although the most intensive spawning occurs in March-April at depths of 500-700 m. In the region of the Grand Banks and probably St. Pierre Bank the spawning of witch flounder continues up to September according to the occurrence of eggs and distribution of spawning fish. However, the most intensive spawning in these areas appears to take place in July-August, with a possible earlier peak in April. Spawning occurs over the whole area of the Grand Banks in shallow water and on the slopes, although accumulations of eggs and new larvae suggest that the most intensive spawning is associated with the slopes of the bank greater than 500 m.

Judging by the occurrence of eggs in the waters of Georges Bank and the Scotian Shelf, spawning in this area begins in May and probably even earlier, with the peak spawning period around July-August and some spawning as late as October.

Although detailed information on spawning of witch flounder in the Gulf of St. Lawrence is sparse, it is known that in January-February they form a large prespawning concentration in the Laurentian Channel just southwest of St. George's Bay. Preliminary observations on the stages of maturity of these fish in January would suggest that peak spawning in this area may take place in late spring or early summer.

The pelagic or midwater stage in the life history of witch flounder is longer than any other of the pleuronectine flatfishes and may continue anywhere from four months to one year. During this time, eggs and larvae from spawning grounds in the northern areas drift southward in the fast Labrador current over great distances to settle in water where temperatures are suitable for survival. Eggs and larvae on the southern banks probably do not drift far because of the slow currents which move in a more circular fashion. On occasion, however, eggs have been found floating over oceanic depths.

Age and Growth

Aging of witch flounder is usually determined by counting annual growth rings on scales or otoliths (ear bones) where one narrow ring represents a winter's growth (when growth is slower) and one wide ring represents a summer's growth. In the early 1950s, when exploitation of witch flounder stocks was low, some 3-year-old fish were caught. However, with heavy exploitation of these stocks in more recent years, few witch flounder are caught now beyond 15 years of age. Witch are a very slow-growing species compared to other flatfishes such as American plaice and yellowtail flounder. As a result, they do not enter the commercial fishery until about nine years of age and are not fully exploitable until about age 13.

Female witch flounder live longer and grow larger than the males. Unlike most other marine fish species in the Northwest Atlantic where the size at age is greater in the more southerly areas, the opposite is true of witch flounder for both males and females. The fastest growth rate occurs in the northeast Newfoundland Shelf area with the slowest growth rate in the Gulf of St. Lawrence area. Growth rates of witch flounder in other areas of the Northwest Atlantic appear to be somewhere between these two.

The size at which these fish reach sexual maturity is smaller for males than for females. Because of this, males do not grow as fast as females. Energy that would normally have been used for growth has to be used for the formation of the sex products, therefore slowing down the growth rate.

Commercial Fishery

The fishery for witch flounder began in the early 1940s with the establishment of the local otter trawling fleet in Newfoundland. Exclusive fishing occurred in Fortune Bay, Newfoundland, using Danish seines in the early 1950s, and in St. George's Bay from 1956 when low catches forced the seiners to move from Fortune Bay. The witch flounder fishery was essentially a byproduct of the very lucrative haddock fishery in the late 1950s and early 1960s on the southwest slope of the Grand Banks. Since the decline in the haddock fishery, witch flounder became a by-catch of the cod fishery and American plaice fishery on the Grand Banks; the cod fishery in the southern Labrador-northeast Newfoundland Shelf; and the fishery for cod, redfish and American plaice on St. Pierre Bank. In the Gulf of St. Lawrence, witch flounder is mainly a by-catch of the otter trawl fishery for cod and redfish in wintertime. There is a more or less small directed fishery by Danish seiners in summertime still carried out in St. George's Bay, with some taken by Danish seiners near Cape Breton Island.

When the witch flounder fisheries came under international quota regulation in 1974, the fishery was divided into five different stock areas for management purposes, based upon the best biological advice at that time. The five stock areas are: (1) Southern Labrador-eastern Newfoundland (NAFO Div. 2J-3KL); (2) Southern Grand Banks (NAFO Div. 3NO); (3) St. Pierre Bank-Fortune Bay (NAFO Sub-div. 3Ps); (4) Northern Gulf of St. Lawrence (NAFO Div. 4RS); (5) Scotian Shelf (NAFO Div. 4VWX).

In the southern Labrador-eastern Newfoundland stock area the fishery is mainly pursued by the Canadian, Polish and USSR otter trawlers, as well as Newfoundland inshore gill net fishermen. There was practically no fishery for witch flounder in this area before the 1960s, consequently, the early catches were from an accumulated virgin stock. However, with the reduction of the previously unexploited stock, catch per hour has been greatly reduced. In Notre Dame, Bonavista and Trinity bays, the inshore boats have been forced to move progressively offshore as closer portions of the stock were depleted. Poland and USSR have taken substantial quantities, in particular from the area just south of Hamilton Bank to Funk Island, probably as by-catches of other fisheries.

Total landings have declined from a high of 24,000 metric tons (t) in 1973 to just over 3,000 t in 1980; however, this drastic difference is not necessarily a true reflection of stock status as much as a heavy reduction in foreign fishing effort. A recent evaluation of stock status does indicate stability in the stock at average annual removals of 8,000 t.

The fishery on the southern Grand Banks stock over the past 15 years has been carried out by both Canadian and Soviet otter trawlers, usually in wintertime along the deep southwest slope where a prespawning concentration is formed. Catches increased from 4,700 t in 1969 to a high of 15,000 t in 1971. They declined to an average of 5,000 t from 1975-80, although catches since 1978 have been just over 3,000 t annually. A total allowable catch (quota) of 10,000 t was placed upon this stock in 1974, and remained in effect until 1979 when it was reduced to 7,000 t. It was subsequently reduced to 5,000 t for 1981 as a result of declining numbers and catch per unit effort.

The witch flounder fishery in St. Pierre Bank is entirely a by-catch fishery of other major groundfish fisheries with a small seiner and gill net fishery carried out in Fortune Bay. A precautionary quota of 3,000 t was placed upon this stock in 1975 and remained since that time. Landings, however, rarely exceed 1,000 t annually and the probability of any increase in directed effort towards this small stock is highly unlikely.

Landings of the northern Gulf of St. Lawrence stock have averaged about 3,500 t since 1975, with the lowest catch in 1975 of 2,000 t and the highest catch of 5,300 t in 1976. A biological assessment of this stock in 1978 indicated the presence of very large old fish up to 26 years of age in the landings. Many of these old fish had to be discarded because of their "jellied" condition and generally poor quality. During spawning season these fish do not feed much, if at all, and the energy required for survival has to be obtained from the body of the fish, leaving behind a soft "jellied" flesh useless for marketing. This condition does not occur in the younger fish. Therefore, it is to the advantage of the fishery to reduce the numbers of very old fish in the stock, which would allow for faster growth in the younger ones through less competition for food. A total allowable catch of 3,500 t introduced in 1977 was therefore increased to 5,000 t in 1979-81 with the intent of stimulating the rate of fish growth and removing the old fish from the population.

A recent biological assessment showed that the oldest age group has now been reduced from 26 to 16 years, with the average size at age having increased considerably. There appears to be no reduction in total weight of the stock and no reports of discards of "jellied" fish. Since this strategy appears to have been successful, the quota for 1982 was returned to its original level of 3,500 t.

The only other regulated witch flounder stock is a small stock on the Scotian Shelf and catch restrictions are part of a combination of a witch flounder, yellowtail flounder and American plaice quota. The total allowable catch on flatfish of the Scotian Shelf was introduced at 32,000 t in 1975. It was reduced to 28,000 t in 1976-77, 14,300 t in 1978 and has remained at 14,000 t since 1979. The fishery is now almost entirely Canadian by offshore otter trawlers. Landings of witch flounder have been relatively consistent since 1977 at a level of just over 2,000 t annually.

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Last updated: 2006-06-06

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