LakeLife: Mountain Whitefish (Prosopium williamsoni)

Originally published in BCLSS Newsletter Volume 17, Issue 1, 2014. Updated January, 2023.

Mountain whitefish (Prosopium williamsoni), also known as Rocky Mountain whitefish, are approximately 15 – 45 cm in length (to a maximum or 58.5 cm) and 0.5 – 1.3 kg in weight (to a maximum of 2.3 kg). Mountain whitefish look quite trout-like but have a much smaller head, a larger adipose fin, larger scales, and no teeth. The snout is pointy and sticks out past the mouth. They are greyish to light brown on the back, silvery on the sides and white on the belly. The scales are relatively large, round and may be outlined with black (EBA, 1998). The short dorsal fin has 12-13 rays, with 11-13 for the anal fin, 10-12 for the pelvic fins, and 14-18 for the pectoral fins (Mountain whitefish, Wikipedia).

Where do they live?

The mountain whitefish is only found in western North America, from Nevada to the Yukon/British Columbia border. It is not found along the coast or further east than the Saskatchewan River in Alberta. It is widespread in British Columbia and can be found in the Columbia, Fraser, Skeena, Nass, Stikine, Dean, Peace, Liard, and Yukon drainage basins. The species occurs in both lakes and streams. It may live in fast water, in small, turbid pools, or cold, deep lakes where it is seldom caught deeper than 20 metres. After hatching, fry are found in shallow water along the shoreline, at stream edges or in protected backwaters. Young fish move into deeper water as they grow (Ractliffe, 1999).

What do they eat?

Mountain whitefish are usually bottom feeders, eating food such as aquatic insect larvae, small molluscs, eggs and sometimes fish. In streams, drifting invertebrates and terrestrial insects are also eaten (Ractliffe, 1999). Mountain whitefish stir up the bottom substrate with pectoral and tail fins to expose insect larvae and other invertebrates, including snails, crayfish, and amphipods (Mountain whitefish, Wikipedia). Their main feeding time is in the evening, but they will also take drifting prey during the day (Mountain whitefish, Wikipedia). The mountain whitefish frequently feeds in the lower strata of streams, but populations may rise to the surface to prey on hatching insects, including mayflies (Mountain whitefish, Wikipedia).

What is their life cycle like?

Mountain whitefish spawn in lakes and rivers and their age at maturity varies between systems (EBA, 1998). Usually, the mountain whitefish becomes sexually mature at the age of three or four years. In BC, spawning typically occurs between November and February over gravel or rocks in streams or in the shallows along the lakeshore (EBA, 1998). They gather in small groups during daylight. Courting begins in the evening but spawning does not occur until after dark. No nest is built for their eggs which simply sink to the bottom and fall between the spaces among the stones. The eggs hatch in the early spring and young fish form schools. Extensive spawning, feeding and over-wintering migrations do occur. Mountain whitefish can live up to 17 or 18 years (Ractliffe, 1999).

How are they doing?

Mountain whitefish is yellow listed, which means that this species is not at risk in British Columbia (BC CDC, 2023). Some populations have likely declined due to habitat degradation.

No kidding!

There is one report of a fish caught in Alberta that was 29 years old (Ractliffe, 1999).
Due to their ability to store toxins, such as mercury, mountain whitefish are used to locate waters containing fish that are unsafe to eat; they are also used in fish health surveys (as a bio-indicator of ecosystem health) (Ractliffe, 1999).

How you can help

It is important to obey angling regulations and habitat protection bylaws, guidelines and regulations since they were designed to protect the fish and their habitat. Please Report All Poachers and Polluters and any violations of the regulations by phoning 1-877-952-7277.
Never transport live fish or other organisms from one body of water to another. You could transfer diseases, parasites, and invasive species from one ecosystem to another or upset the natural balance in the ecosystem where they are released.
Be aware that what goes into your septic tank or roadside storm drain may find its way into streams or lakes. Help keep freshwater systems clean by using detergents and soaps minimally and do not dump harsh chemicals, such as bleach, paint thinner or antifreeze, down drains.
Form a group of water stewards and volunteer to monitor local water quality.
Cultivate an interest in the variety of fish found in the province. They all play an important role in our aquatic ecosystems.

References

B.C. Conservation Data Centre. 2023. BC Species and Ecosystems Explorer. B.C. Ministry of Environment, Victoria, B.C. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jan 9, 2023)

EBA Engineering Consultants Ltd [EBA]. 1998. Species Summary – Mountain Whitefish. Available: https://a100.gov.bc.ca/pub/acat/documents/r10789/8840209-App.A-Speciessummary-MountainWhitefish_1188324864396_f6d9ed881f674be38a50ea8d31322657.pdf (accessed Jan 9, 2023).

Ractliffe, R. 1999. B.C. Fish facts – Mountain Whitefish. BC Ministry of Fisheries. Available: https://a100.gov.bc.ca/pub/eirs/finishDownloadDocument.do?subdocumentId=997 (accessed Jan 10, 2023)

Wikipedia. N.d. Mountain whitefish. Available: http://en.wikipedia.org/wiki/Mountain_whitefish (accessed Apr 9, 2014).