Inconnu (Stenodus leucichthys)

On this page

• Species overview
• Fishery history
• Ecosystem context
• Science advice and research
• Sources

Species overview

Physical description

Inconnu is a large, long fish in the salmon family, closely related to Whitefish. It has a long, wide head with a lower jaw that protrudes past the upper jaw and a strongly forked caudal fin. Inconnu is silver with a light green-brown back and clear fins. The dorsal and caudal fins have dark tips. It typically grows to be 450 to 760 millimetres (mm) long, but have been known to reach up to 1.1 metres.

Distribution

Inconnu is found in northwestern North America and in northern Asia. In North America, populations are located in:

• Alaska
• Northwest Territories
• Yukon
• northern British Columbia

Inconnu occupies cold waters shallower than 40 m, but more commonly less than 30 m.

Life cycle

Most populations of Inconnu are anadromous, moving from saltwater to freshwater for spawning. There are also potamodromous populations that remain in freshwater for their entire life cycle, moving from lakes to rivers and tributary streams for spawning . In Canada, Inconnu in the lower Mackenzie River area is anadromous, while the Great Slave Lake stocks are potamodromous.

Inconnu spawns in the fall, with individuals spawning every 2 to 4 years. Migration to spawning grounds begins in the summer and can take months, while migration back to lakes or the sea is much faster.

Young Inconnu stay in the tributaries where they hatch for at least 2 years before migrating. In Great Slave Lake, Inconnu has been known to experience rapid growth at age 4 due to a dietary switch from benthic invertebrates to fish.

Inconnu is a fast growing species but takes a long time to mature, typically reaching maturity between 7 to 10 years. Anadromous populations mature later than potamodromous populations. Inconnu can live up to 11 years in Great Slave Lake and up to 21 years in Siberian areas.

Fishery history

Inconnu is caught in commercial, recreational, and subsistence fisheries. In Great Slave Lake, a commercial fishery for Lake Whitefish began in 1945 and Inconnu was commonly caught as a bycatch species. In the late 1970s, targeted Inconnu harvest increased and some stocks have still not recovered.

Today, Inconnu is still caught in Great Slave Lake but is carefully managed along with Lake Trout and Lake Whitefish. Some stocks have been extirpated completely, including:

• Hay River
• Yellowknife River
• Taltson River
• Little Buffalo River

Ecosystem context

Threats to Inconnu include:

• industry-related habitat alterations (e.g., fragmentation and habitat loss)
• pollution
• changing water levels
• climate change
• over-harvesting

Inconnu is vulnerable to over-harvesting because it:

• has predictable spawning runs
• gathers in pre-spawn aggregations
• lives in inshore habitats
• is a long-lived species that grows fast but matures at an older age

Science advice and research

Science advice and research for Inconnu

Sources

• DFO. 2013. Assessment of Buffalo River Inconnu (Stenodus leucichthys) Great Slave Lake, Northwest Territories, 1945-2009. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2012/045.
• Howland 2005. Population differentiation of inconnu, Stenodus leucichthys, in the Mackenzie River system. PhD Thesis. University of Alberta.
• Scott and Crossman 1973. Freshwater fishes of Canada. Department of Fisheries and Oceans. Fish. Res. Board of Can. Bulletin 184.
• VanGerwen-Toyne et al. 2013. Information in support of assessment of Buffalo River Inconnu, (Stenodus leucichthys), Great Slave Lake, Northwest Territories, 1945-2009. DFO Can. Sci. Advis. Sec. Res. Doc. 2012/069. vii + 81 p.
• Wiens, et al. 2021. Genetic assessment of Inconnu (Stenodus leucichthys) in Great Slave Lake, Northwest Territories, Canada. 234: 105784.
• Zhu et al. 2017. Establishment of ecological baseline metrics for integrated ecomonitoring and assessment of cumulative impacts on Great Slave Lake fisheries ecosystems. Can. Tech. Rep. Fish. Aquat. Sci. 3223: x + 58 p.