Deepwater sculpin (Myoxocephalus thompsonii), various populations: chapter 7

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Habitat

• Habitat Requirements
• Habitat Trends
• Habitat Protection/Ownership

Habitat Requirements

Deepwater sculpin is a bottom-dwelling species and is only found in deep, cold freshwater lakes throughout northern North America (Stewart and Watkinson 2004). Unlike many other freshwater cottids, its distribution is both patchy and limited solely to deepwater lacustrine environments. The fragmentation is natural; due to the current habitat requirements of the species and the historical glacial lake connections required for its dispersal (Dadswell 1974). Generally, deepwater sculpin co-occur with the glacial relict crustaceans, Mysis relicta and Diporeia spp. (Scott and Crossman 1973; Dadswell 1974).

Throughout the summer of 2004, habitat measurements were taken from deepwater sculpin locations from 20 inland lakes across Canada (T. Sheldon, unpubl. data). The measurements were taken within each lake from specific locations where deepwater sculpin were captured. The ranges, means, and both upper and lower confidence intervals, of these measurements are reported in Table 3. The data suggest that deepwater sculpin require cold, highly oxygenated water (T. Sheldon, unpubl. data). When the maximum depth exceeded 50 m in these oligotrophic lakes, deepwater sculpin were commonly found from 50 m to the maximum depth of the lake. However, in lakes which were less than 50 m deep, deepwater sculpin were most commonly caught within the deepest 20% of the lake only (T. Sheldon unpubl. data). As latitude increases, this relationship seems to weaken and deepwater sculpin are commonly found at shallow depths as well (McPhail and Lindsey 1970).

Data collected using sample bottle at geographic and bathymetric location where specimens caught. Depth - depth of capture; Temp - temperature; SDV - Secchi disk visibility; Oxygen – dissolved oxygen; TDS - total dissolved solids; ORP - oxidative reduction potential; Sp. Cond - Specific conductivity.

Adults in the Great Lakes are usually found between 60 and 150 m. For example, in Lake Ontario, they have been most abundant in the 90-to-110-m range (Fig. 5) (J. Casselman, unpubl. data). In Lake Superior, deepwater sculpin are most common at depths greater than 70 m and have been found as deep as 407 m (Selgeby 1988). Drifting larvae, which were assumed to have been transported from a relatively abundant population in southern Lake Huron, were collected in the St. Clair River in 1990 and in the 2-to-5-m depth range (probably atypically shallow for the life stage and species) in the west end of Lake Erie in 1995 (Roseman et al. 1998).

According to their distribution in Lake Ontario, deepwater sculpin seem to prefer temperatures of <5°C (J. Casselman, unpubl. data). In Lake Huron, they are rarely found in water shallower than 55 m, although the temperature may be <4°C at such depth (J. Schaeffer, unpubl. data).

Figure 5: Contour Map of Lake Ontario Showing Band of Deepwater Sculpin Habitat, Delineated by the 90-to-110-m Contours

The 60-m and 150-m contour lines are also indicated. Provided by J.M. Casselman, Department of Biology, Queen’s University, Kingston, Ontario.

Habitat Trends

Heney Lake and Lac des Iles in southwestern Quebec, two locations where deepwater sculpin have been found historically, have become more eutrophied over the past two decades. In 2004, dissolved oxygen levels of 3.18 and 6.07 mg/L were recorded during the month of August for Heney lake and Lac des Iles, respectively (T. Sheldon, unpubl. data). These measurements were taken from the bottom of the lakes, near the deepest point, where deepwater sculpin are most often found. Both of these oxygen measures are lower than the ranges, and significantly lower than the mean, of measured dissolved oxygen levels of deepwater sculpin locations obtained during the 2004 survey, indicating that suitable deepwater sculpin habitat in these lakes may have disappeared or, at the very least, be declining. Deepwater sculpin were not found in either of these lakes during the survey.

Because deepwater sculpin are unable to exploit new habitats due to dispersal limitations, and suitable habitat may be declining in some lakes in the eastern portion of their range due to eutrophication caused by anthropogenic effects, there has been a small overall decrease in the habitat available for deepwater sculpin.

Habitat Protection/Ownership

In Canada, the deepwater sculpin occurs in publicly owned waters, and all fish habitat within these waters is protected by the federal Fisheries Act. In addition, it occurs in Upper Waterton Lake in Waterton National Park of southwestern Alberta. Therefore, its habitat may receive additional protection afforded to national parks through the National Parks Act.