Aquatic Species at Risk – Arctic Cod (Arctic Lakes populations)

Description
Habitat
Threats
Further Information
Scientific Information

Description

The Atlantic Cod (Gadus morhua) is a member of the family Gadidae and has the following characteristics:

• Classic, streamlined shape;
• Three dorsal fins, two anal fins, a single chin barbel and a very distinct lateral line;
• Colour is brown to green, with spots on the lateral and dorsal surface;
• Arctic Lakes populations are dominated by smaller individuals, with few large individuals;
• Cod in the ocean may grow to lengths exceeding 2 m, while maximum length within the Arctic Lakes populations appears to be slightly less than 1.5 m; and
• Maximum length of 1.57 m (Ogac Lake, Nunavut).

Habitat

Distribution map of the Atlantic Cod (Arctic Lakes populations) on southeastern Baffin Island.

Marine populations of Atlantic Cod are the original source of the Arctic Lakes populations; they consist of three separate populations. Atlantic Cod in the arctic lakes inhabit three saltwater, coastal lakes on southeastern Baffin Island; Lakes Ogac, Qasigialiminiq and Tariujarusiq.

Atlantic Cod are generally found in waters ranging from 2 to 11°C, but due to their ability to produce plasma antifreeze proteins, they are able to withstand temperatures as low as -1.5°C without ice crystals forming in the blood. The landlocked populations in the Arctic are separated from the coastal environment and have become genetically distinct from their marine cousins, and from each other. Seawater enters these lakes only during the highest summer tides. These arctic lakes are considered meromictic, or stratified, and have a freshwater layer of water a few metres deep, with a larger saltwater layer beneath it. The cod live only in the saltwater layer, except for very short trips into the freshwater layer. Spawning involves complex behaviours for mate selection, and occurs in water depths up to 30 m. The number of eggs ranges from 300,000 to several million for larger females. Due to this high fecundity, Atlantic Cod do not build nests or provide parental care. The Arctic Lakes populations are dominated by the smaller-sized Cod, with few large individuals.

Threats

While angling pressure may become a larger concern, it is the small number of locations available for these populations, and the small area of these lakes that are the main threats to this population. The combined surface area of the three lakes is less than 20 square kilometres, suggesting this small area and restricted distribution may be especially sensitive to disturbance. The lakes themselves are unique habitats and may be easily disturbed. No other fish occur in these lakes and the cod rely on high tides to bring in food. Changing sea levels and the resultant tide levels would likely affect these populations of Atlantic Cod. Immigration of other Atlantic Cod populations is highly unlikely, due to the isolated nature of these lakes as well as the shallow and temporary inlet/outlets.

Further information

For further information, visit the SARA Registry at www.registrelep-sararegistry.gc.ca or www.COSEWIC.gc.ca.

Scientific information
Scientific name: Gadus morhua
SARA Status: Under consideration
COSEWIC Status: Special Concern (April 2010)