COSEWIC assessment and status report on the Atlantic wolffish Anarhichas lupus in Canada
Limiting Factors and Threats
There are no direct studies of factors responsible for the declines observed in wolffish abundance. Following the northern cod collapse off Newfoundland in 1992, a number of causes for the cod decline were suggested, including especially environmental changes. On a community level, similar declines in both commercial and non-commercial fish species there seemed difficult to understand without invoking such causes (Gomes et al., 1995). The emerging consensus since then, however, is that while environment may have played some role, overfishing was clearly the major cause of the declines observed in most groundfish species (Sinclair and Murawski, 1997; Villagarcía et al., 1999). And, when assessed over only a slightly longer time scale, fishing in the area is argued to have been responsible for the extraordinary decline of the large and once abundant and widely distributed barndoor skate, Raja laevis (Casey and Myers, 1998).
The Atlantic wolffish has been landed from commercial fisheries for many years. Once a directed target of the western Greenland fishery, it is now taken incidentally as by-catch only. There, Möller and Rätz (1999) report that calculated wolffish mortality is positively correlated with commercial landings of cod and shrimp. This indicates that fishing for other species can have a negative impact on wolffish through removal in the by-catch. There is no directed fishery for the Atlantic wolffish in Canadian waters, though it is taken as by-catch by offshore trawlers. Recently, wolffish filets have begun to appear on occasion in St. John’s fish shops.
In fisheries data compiled by the Food and Agriculture Organization of the United Nations (FAO), wolffish landings for the western North Atlantic are reported for the whole family (3 species) rather than for each individual species; the Atlantic wolffish comprises the majority of those landings in Canada (Kulka and DeBlois, 1997). While the eastern North Atlantic wolffish fishery (apparently focused more on the spotted wolffish, A. minor; Wheeler, 1969) has had annual landings of around 30,000 tonnes since the late 1950s, with two peaks of over 50,000 tonnes in 1962 and 1974, the western North Atlantic fishery has always been smaller. Northwest Atlantic landings (Figure 9) hovered around 5,000 tonnes through the 1950s and then rose through the 1960s and 1970s to a peak of 22,000 tonnes in 1979. Landings then declined steadily through the 1980s and 1990s; in 1984 they stood at 6,000 tonnes and by 1996 had fallen to 1,700 tonnes.
Figure 9. History of the northwest Atlantic fishery for Atlantic wolffish, Anarhichas lupus, 1950-1996. FAO Data.
The principal northwest Atlantic countries involved throughout in the history of the wolffish fishery have been Canada and Greenland, each with about a third of the landings from 1950 through 1996. The Soviet Union and East Germany also played significant roles in this fishery through the 1960s and 1970s, with East Germany responsible for almost 70% of 1979's record catch. The Soviet Union and East Germany were essentially out of the picture by the early 1980s, and by 1990 Greenland had seriously curtailed its fishing efforts as well. In recent years, from 1990 through 1996, Portugal has become the major participant in a much reduced fishery.
Apart from the direct adverse impact of fisheries on Atlantic wolffish, human activities also have indirect and detrimental effects on this species. The groundfish trawls, generally otter trawls, in which wolffish are caught also result in incidental mortality and damage to fish which come in contact with the mobile fishing gear but are not caught. Perhaps even more importantly, the steel doors or otterboards of the net, along with heavy bottom lines and rollers, scour the seabed as they are dragged across it (Watling and Norse, 1998). This practice may cause significant habitat damage by removing or re-distributing the rocks and boulders under which these fish shelter, spawn and build nests. Studies on Georges Bank (Collie et al., 1997) and in the Gulf of Maine (Auster et al.1996), areas within the southern limit of the Atlantic wolffish's range, show the considerable degree of damage that can result from bottom dragging there. Jennings and Kaiser (1998) provide an excellent overview of the entire question of fishing impacts on habitat; they point out that these can vary quite a bit depending on local conditions, but suggest that the greatest and most lasting impacts are most likely to occur on hard substrates in deep water, i.e. just those habitats favoured by the Atlantic wolffish.
Bottom trawling for fish and dredging for scallops and clams, in addition to digging up and disrupting bottom habitats, also resuspends bottom sediments, which can smother spawning areas and damage gills. Resuspension of sediments may change the sediment chemistry or release settled toxic heavy metals. Other human activities such as channel dredging and aggregate extraction may do considerable harm to bottom habitats by destabilizing the seabed, increasing erosion, and polluting previously healthy areas (Messieh et al., 1991).
The period since 1992 is an anomalous one for all Canadian waters. Relative to the past, fish populations are at an all-time low. For that reason, bans on fishing (moratoria) have been in effect in most regions for various periods of time, and these continue. Fishing predation is thus much relaxed, and populations should do better as long as that situation continues, which will not be forever. A cornerstone in the Fisheries Resource Conservation Council's approach to management (this quasi-independent group advises the Minister on the status of commercial fish stocks) is adherence to the precautionary principle (FRCC, 1996). That principle -- when in doubt, err on the side of the fish -- should also apply in regard to COSEWIC status.
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