Aquatic Species at Risk - Deepwater Sculpin (Great Lakes - Western St. Lawrence populations)

Deepwater Sculpin (Great Lakes - Western St. Lawrence)

Deepwater Sculpin

SARA Status: Special Concern
Special Concern

Region: Ontario, Quebec

Region: Ontario, Quebec

Did You Know?

The freshwater and marine forms of the Fourhorn Sculpin (M. quadricornus) are two closely related taxa that resemble the Deepwater Sculpin. However, they have four horn-like spines on top of the head, which are lacking in the Deepwater Sculpin.

Related Information

COSEWIC assessment and update status report on the deepwater sculpin Myoxocephalus thompsonii (Western and Great Lakes-Western St. Lawrence populations) in Canada (2006)


The Deepwater Sculpin (Myoxocephalus thompsonii) is a lake-dwelling sculpin of the family Cottidae. It has the following characteristics:

  • Flat, long body averaging 47.2 to 110.5 mm total length with a mean of 76.7 mm total length;
  • Eyes on top of the head;
  • Lacks true scales;
  • Large mouth with small teeth on both jaws, tongue, and roof of mouth;
  • Separated dorsal fins; the first has 7 to 10 spines, the second has 11 to 16 soft rays;
  • Large pectoral fins, reduced pelvic fins, long base on anal fin, square or truncated caudal fin;     
  • Dark grey to brown in colour with dark saddles marking the back; light speckling on sides; pale belly; and
  • Three dark bands on pectoral fins; lightly spotted pelvic fins; faintly blotchy dorsal and anal fins.
Deepwater Sculpin

Myoxocephalus thompsonii
© J. R. Tomelleri


Deep Sculpin Distribution as described in the following paragraph

The distribution of the Deepwater Sculpin is almost entirely limited to Canada with the exception of the American Great Lakes and a few inland lakes in Michigan, Minnesota and Wisconsin. In Canada, its distribution is patchy and limited to cold, deep lakes in areas that were formerly glaciated or with proglacial lake connections. This includes the Mont-Laurier region of Quebec through the Laurentian Great Lakes, continuing through Manitoba, Saskatchewan, and Alberta, and northwest to Great Bear and Great Slave lakes in the Northwest Territories. The Great Lakes – Western St. Lawrence designatable unit (DU) is listed as Special Concern under the SARA. This DU encompasses ten lakes in Ontario and Quebec.

Deepwater Sculpin occur in more than 60 different lakes in Canada. However, within the Great Lakes - Western St. Lawrence population, they are known to occur in only 10 lakes. In Ontario, Deepwater Sculpin occurs in lakes Nipigon, Ontario, Superior, Fairbank and Huron. Only larvae (young-of-the-year) have been observed in Lake Erie; however, these are believed to have originated in Lake Huron and there is no reproducing population in Lake Erie. In Quebec, Deepwater Sculpin occurs in Grand Lac Rond, Lac des Iles, Heney Lake and Thirty-One Mile Lake. However, populations in Heney Lake and Lac des Iles may be extirpated.

The Deepwater Sculpin is a bottom-dwelling fish that is found in cold (<7ºC), well oxygenated, deep lakes. In the Great Lakes, adults usually live between 60 and 150 m in depth. For this reason, not much is known about the biology of this fish. The reproductive cycle is not well understood and habitat requirements for spawning are largely unknown. Spawning appears to occur during the winter in the Great Lakes; however, it is unknown if timing is similar in smaller inland lakes. It appears that individuals from the Great Lakes, especially Lake Ontario, are generally larger compared to other populations. Deepwater Sculpin are an important dietary component for Lake Trout and Burbot.

The diet of Deepwater Sculpin consists largely of Mysis relicta, Diporeia spp. and chironomid larvae. Zooplankton likely comprises the diet of the larval stage, which is pelagic (open water). Secondary food items can include trichopteran larvae, sphaeriid clams, ostracods, leeches, fish eggs, and small fishes.


Deepwater Sculpin is primarily threatened by habitat loss, habitat degradation and aquatic invasive species. Water quality is declining as a result of industrial, urban and agricultural developments, which is a significant threat in inland lakes. The enrichment of lakes with nutrients (eutrophication) and the resulting low oxygen levels in bottom waters likely contributed to the decline of the Deepwater Sculpin in Heney Lake and Lac des Iles. The extirpation or near extirpation of Deepwater Sculpin from Lake Ontario has been linked to the invasion of Alewife (Alosa pseudoharengus) and Deepwater Sculpin is likely impacted by changes in zooplankton species composition and abundance. For example, a decline in Diporeia spp. in the lower Great Lakes may pose a threat to this fish since it is an important food source.

Further information

For more information, visit the SARA Registry.

Text Sources: COSEWIC assessment and status report on the Deepwater Sculpin in Canada, 2006; Fisheries and Oceans Canada. Management Plan for the Deepwater Sculpin, Great Lakes-Western St. Lawrence populations in Canada [proposed], 2013.

Scientific information

Scientific Name: Myoxocephalus thompsonii
SARA Status: Special concern (December 2007)
COSEWIC Status: Special Concern (April 2006)