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Recovery Strategy for Northern Wolffish and Spotted Wolffish, and Management Plan for Atlantic Wolffish in Canada [Final]


2. Distribution

2.1 Global Range

Wolffish (Family Anarhichadidae) inhabit a wide range of northern latitudes and moderately deep waters in the Atlantic, Pacific and Arctic Oceans. The genus Anarhichas is widely distributed in both the eastern and western North Atlantic, the three species having somewhat overlapping distributions. In addition to its distribution in the northwest Atlantic, A. denticulatus occurs in the eastern Atlantic from Greenland, Iceland, the Faroe Isl., Finnmarken, Murman Coast, and Novaya Zemlya. A. minor occurs in the eastern Atlantic from Greenland, Iceland, the Faroes, Spitsbergen, White Sea, off the Murman coast, around Scotland, and on the Norwegian Coast south to Bergen. A. lupus occurs in the eastern Atlantic from Greenland, Iceland, the Faroes, Spitsbergen, White Sea, Murman Coast, south to the British Isles, and the western coast of France (Scott and Scott 1988).

2.2 Eastern Canadian Range

A. denticulatus, A. minor and A. lupus occur in the western North Atlantic from the Davis Strait to the Gulf of Maine. The distribution of A. lupus extends south of eastern Canadian waters, as far south as Cape Hatteras.

More specifically, A. denticulatus occurs from as far north in the Davis Strait at Lat.72°N off Nunavut (northern limit), off southwest Greenland, on the northeast Newfoundland and Labrador Shelves (center of concentration), on the Flemish Cap, in the Gulf of St. Lawrence (uncommon), on the Grand Bank and rarely on the Scotian Shelf (Banquereau and Sable Island Bank), Lat. 42°N. Similarly, A. minor occurs off west Greenland (northern limit at about Lat.72°N), on the northeast Newfoundland and Labrador Shelves (center of concentration), the Grand Banks, on the Flemish Cap, in the Gulf of St. Lawrence and on the Scotian Shelf. A. lupus has a slightly more southern distribution occurring from west Greenland, on the northeast Newfoundland and Labrador Shelves, in the Gulf of St. Lawrence, on the Grand Bank, on the Scotian Shelf, in the Bay of Fundy, and in the Gulf of Maine (Simpson and Kulka 2002, Scott and Scott 1988). A. lupus is common in the Gulf of St. Lawrence, on the Scotian Shelf and in the Gulf of Maine, where the other two species are uncommon or rare. Refer to Figure 2 (a, b and c) for a map of the distribution of the species from the Grand Banks to the Labrador Shelf, the center of their concentration.

2.3 Percentage of Global Distribution in Eastern Canadian Waters

Percentage of global distribution occurring in eastern Canadian waters is not known for any of the species. In Canadian Atlantic waters, each of the species occupies an area of about 500,000 km2, a significant portion of the global distribution. Although the three species of wolffish are widely distributed in the western Atlantic and thus constitute a significant portion of the global population, A. lupus is more densely concentrated to the south and east of Greenland (east of Canada’s territorial limit) where they are dense enough to be the target of a directed commercial fishery.

2.4 Distribution Trends in Eastern Canadian Waters

Fisheries and Oceans Canada (DFO) carried out standard stratified random surveys in the Canadian Atlantic. However, the resulting survey series constitute relative indices because the catchability of wolffish (and other species) is unknown and the series are not comparable among DFO Regions because of different gears and protocols used. The extent of the two threatened wolffish species is far greater in areas of the Newfoundland and Labrador Region, and therefore this is thought to constitute the centre of its distribution. As well, the greatest decline occurred in this area. As such, this document is focused mainly on the Newfoundland and Labrador Region.

On the Grand Banks to the Labrador Shelf between 1977 and 2002, Newfoundland and Labrador regional fall research surveys recorded catches of all three species of wolffish widely distributed throughout the Labrador and northeast Newfoundland Shelves to the southern Grand Banks, the center of their distribution in Canadian waters (Simpson and Kulka, 2002, Kulka et al., 2004).

The area surveyed in the fall covers two distinct areas of distribution based on habitat characteristics. The northern area covers the Southern Labrador Shelf and the Northeast Newfoundland Shelf. There, all three wolffish species were present along the entire shelf to the coast, particularly prior to the decline. This area comprises mainly rocky substrate. To the south on the Grand Bank, the three species inhabit only the periphery of the bank along the shelf edge, with the exception of A. lupus that forms a concentration on the southern Grand Bank where the bottom is mainly pebble, sand and mud. Figure 2 (a, b and c), shows the change in distribution between the early 1980s and the 1990s. These aggregate plots of wolffish distributions for the time periods 1980-1984, 1985-1993 and 1994-2001 show a declining distribution in both intensity (lower catch rates) and extent of the distribution of the three wolffish species. This reduction in the area occupied coincides with an observed decline in the biomass and abundance estimates of these species (Simpson and Kulka 2002, Kulka et al. 2004).

In years when the Flemish Cap was sampled, the three wolffish species were also found in abundance there. Surveys were sporadic in the Arctic, but fisheries in Davis Strait as far north as Lat.72°N occasionally capture A. denticulatus and A. minor, describing the northern limit of the distribution. For A. denticulatus, large catches occurred throughout the northeast Newfoundland Shelf and the Labrador Shelf during the early 1980s. However, from 1986-2001, the distribution of larger catches of A. denticulatus was increasingly limited to the shelf edge throughout the entire survey area. Similar to the distribution of A. denticulatus, the catches of A. minor and A. lupus were increasingly limited to the periphery of the northeast Newfoundland and Labrador Shelves and the Grand Banks from the mid-1980s to 2001 (Kulka et al. 2004). Overall, the distribution of all three species of wolffish has contracted in recent years relative to their distributions during the 1970s and early 1980s.

A. lupus has a distinguishing feature in terms of its distribution on the Grand Banks. In addition to large catches on the bank edges as is the case for all three species, A. lupus is also captured in shallower waters on the southern Grand Bank, a circular on-shelf concentration, where the other two species are not found (Figure 2 a, b and c).

Between 1980 and 1984, A. denticulatus were widely distributed throughout the area north of the Grand Bank covering much of the shelf, the eastern Grand Bank shelf edge and the Flemish Cap. From 1985 to 1993, there was a decline in the extent and intensity of the distribution of A. denticulatus. Most recently, A. denticulatus have been concentrated only on the shelf edge, the edge of the southern Grand Bank and the Flemish Cap.

Prior to 1986, A. minor were extensively distributed north of the Grand Banks covering much of the shelf, with a few occurrences along the eastern Grand Bank shelf edge and the Flemish Cap. Between 1985 and 1993, previously observed areas of high density had disappeared, the distribution reduced to low density concentrations along the shelf edge and in deep channels. Most recently (1994-2001), there were no significant concentrations of A. minor compared to previous time periods.

Similar to the pattern observed for A. denticulatus during 1980-1984 north of the Grand Banks, A. lupus were widely distributed covering much of the northeast Newfoundland and Labrador shelves. In addition, a separate aggregation of A. lupus centered at Latitude 44°N, west of the Southeast Shoal on the tail of the Grand Bank was also apparent, well separated from the concentrations on the Labrador Shelf. During 1985-1993 and 1994-2001, there was a reduction in the extent and intensity of the northern component of A. lupus; however, the southern Grand Bank concentration remained relatively unchanged or increased slightly.

On the Scotian Shelf, the general pattern of distribution of A. lupus has remained relatively consistent over the 30-year history of the summer survey (McRuer et al. 2001). A. lupus are found over the entire Scotian Shelf, but in recent years, there have been reduced numbers in the mid-shelf regions and greater numbers along the Laurentian Channel and northeast Scotian Shelf. There are also concentrations in the approaches to the Bay of Fundy and around Browns, Roseway and LaHave Banks (McRuer et al. 2001).

Although few A. lupus are caught during the fall surveys of the southern Gulf of St. Lawrence, their distribution has gradually expanded in recent years (McRuer et al. 2001). During 1971 - 1980, A. lupus catches were restricted to a few areas along the slope of the Laurentian Channel. Since the 1980s, they have been caught along most of the slope of the Laurentian Channel and into the Cape Breton Trough, with small catches in shallower water (i.e., < 100 m) off the coasts of eastern Prince Edward Island (PEI) and the Acadian Peninsula. A. lupus have never been observed on the Magdalen Shallows in the central Gulf (McRuer et al. 2001).

Data from surveys in the northern Gulf of St. Lawrence show very little change in distribution (McRuer et al. 2001). A. lupus tended to be concentrated mainly along the coast of western Newfoundland and in the northeastern Gulf. Similar distributions were seen in the July and October sentinel surveys, conducted since 1995. The October series, however, shows the fish further offshore than either the research or the (July) sentinel survey, suggesting that the fish may move to deeper water in the fall.

At their center of concentration, both the relative and absolute area occupied by high, medium and low density concentrations of all three species declined from the high density periods of 1980-1984 relative to the current low density periods, 1995-2001 (Figure 3 upper panel; refer to Simpson and Kulka 2002 for a definition of density levels). The decline in the area occupied by high densities of wolffish was most pronounced for A. denticulatus, (55%), and least pronounced for A. lupus (38%), (Simpson and Kulka, 2002, Kulka et al. 2004). The area occupied by high density A. minor concentrations declined by 47%. The middle panel of Figure 3 shows that the overall area of occupancy also declined since the 1980s for the three species, but was most pronounced for A. denticulatus, and least pronounced for A. lupus. The concentration of A. lupus on the southern Grand Bank actually increased slightly (Figure 3 lower panel).

On the Scotian Shelf, the area occupied index (defined as the proportion of the annual survey sets in which a species occurs) for A. lupus has been lower in the 1990s following a decline in the 1980s. In the southern Gulf of St. Lawrence, this index increased during the early 1980s and has remained at slightly higher values since then. This index was not available for the northern Gulf of St. Lawrence (McRuer et al. 2001).

Wolffish young of the year (YOY), identified as A. lupus, were captured in IYGPT (International Young Gadoids Pelagic Trawl) sets conducted from 1996-1999 (August and September). They were widely distributed offshore on the northeast Newfoundland and Labrador Shelf (Simpson and Kulka, 2002). It is possible that some of those YOY taken in the survey comprised other species of wolffish since fish of that size are difficult to distinguish to the species level. Small (<55cm in length) wolffish, captured in the fall trawl surveys were also found to be distributed extensively in similar offshore areas. Overall, there is considerable overlap in the distribution of small and large (> 55 cm) A. minor and A. lupus including YOY. In the case of A. lupus, there was an increase in the size of catches of small fish from 1995 to 2000 along the edge of the northern shelf and on the southern Grand Bank. For A. minor, there has been no apparent increase in the proportion of small fish in recent years.