INTRODUCTION TO THE FRESHWATER FISHES OF BRITISH COLUMBIA
Professor, Department of Zoology, University of British Columbia
Director, Beaty Biodiversity Museum
The freshwater fishes of British Columbia (BC) consist of 67 native species and 15 introduced species. By comparison, Ontario has 131 native species and at least 28 introduced species. “Freshwater” species either spend their entire lives in freshwater or may spend time feeding in salt water before returning to freshwater to spawn. The latter are known as anadromous fishes (e.g., Pacific salmon). Other species that reproduce in salt water, but spend time feeding in fresh water are known as catadromous fishes (e.g., American eel), but BC contains no such species.
The most diverse group of freshwater fishes in BC is the Salmonidae – the salmon, trout, char, grayling, and whitefishes – with some 22 species (of which three are introduced). The least diverse are the trout-perches (Percopsidae), pikes (Esocidae), and cods (Gadidae) each with one species.
Origin of the BC freshwater fish fauna
The first “record” of freshwater fishes in BC dates back to about 50 million years ago (mya) and is associated with the discovery of the fossil salmonid fish, Eosalmo driftwoodensis, the specific name stemming from its discovery near the Driftwood River in BC’s central interior. The ancestry of BC’s freshwater fishes, however, dates back much farther into the mists of time. The lampreys, of which BC has four species, are descendants of one of the very earliest lineages of vertebrates, a lineage that split from the rest of the vertebrates at least 500 mya. Also, many of the extant families of BC freshwater fishes date to at least 65 million years ago in North America. The first fossils that are clearly recognizable as the same as living fishes (e.g., white sturgeon and cutthroat trout) have been dated to about 5 mya, in the Pliocene. At the other end of the time continuum are native species that are probably less than 10,000 years old. The world-famous “benthic” and “limnetic” species pairs of threespine sticklebacks (part of the Gasterosteus aculeatus species complex) are found in four lakes southwestern BC and are considered to have evolved since the retreat of the Wisconsinan glaciers.
Biogeography of the BC freshwater fish fauna
The history of the BC freshwater fish fauna has been heavily influenced by four processes, three of which are driven by geography: mountain-building, volcanism, glaciation, and human activity. The first three extent back millions of years and continue to the present day; the most serious human activities are limited to the past 200 years or so (the “Anthropocene” see below).
Mountain-building and shifting of the Rocky Mountains and the Coastal/Insular mountain ranges concentrated between 33 and 65 mya set the major pattern of river flow in BC; the predominate eastern (Peace and Liard rivers as part of the Mackenzie River system) and western-flowing (all other river systems) drainages. Extensive volcanism from 23 – 3 mya helped to produce the heavily sculpted waterscapes of the central interior of BC. Finally, the Wisconsinan glaciation, one of up to 20 that occurred during the Pleistocene, lasted from about 85,000 to ~11,000 years ago and covered virtually all of BC with ice sheets up to 3 km thick which eliminated all of the habitat for freshwater fishes. Consequently, the current native fish diversity of BC stems almost exclusively from post-glacial immigration of fishes that survived glaciation in ice free areas north, west, east, and south of the ice sheets (known as “glacial refugia”).
There were three principal glacial refugia that provided postglacial immigrants to BC via now extinct inter-watershed connections: the Bering Refuge (unglaciated areas of the Yukon River valley and adjacent areas of eastern Russia), the Pacific Refuge (unglaciated areas of the lower Columbia River valley and adjacent areas), and the Great Plains Refuge (unglaciated areas of the upper Missouri River east of the Continental Divide). The Pacific Refuge is thought to have provided the greatest source of postglacial immigrants (about 37 species). Some fishes in BC (e.g., the stickleback species pairs, the Salish sucker and the Nooksack dace) and considerable intraspecific diversity (e.g., the thousands of genetically distinct salmon and trout populations) are considered to have evolved in situ since the end of the last glaciation and are, in this sense, “made in BC biodiversity”.
Currently, one way in which we organize BC’s freshwater fish biodiversity is by the major watersheds that share a high proportion of fish species: the upper Yukon River, the Mackenzie River, the upper Columbia River, the Fraser River, the Central Coast, the North Coast, Vancouver Island, and the Queen Charlotte Islands. The Mackenzie River system is the largest in BC at about 260,000 km2 and the Queen Charlotte Islands is the smallest drainage area at 14,500 km2. The Fraser River system has the largest number of native species (42) while the Queen Charlotte Islands has the lowest number (14 species)
The “Anthropocene” has been defined informally as that period in geological time when humans began having a profound effect on Earth’s ecosystems (commonly, but not universally accepted to begin at the start of the Industrial Revolution). In BC, one of the most profound effects of the Anthropocene has been the introduction of non-native fishes. Such introductions threaten the persistence of native species and disrupt the historical faunal relationships as part of Canada’s bioheritage (see Taylor 2004). The Columbia River has the highest number (16) of non-native species, while the Queen Charlotte Islands and the upper Yukon River have, thankfully, no non-native species.
By contrast, there are, as yet, no known extinctions of BC’s freshwater fish species at least at the level of full species. There have, however, been several important extinctions of BC’s freshwater fish biodiversity; the extinction of all of the innumerable Chinook salmon populations from vast areas of the upper Columbia River after completion of the the Grand Coulee Dam in Washington State in 1942 (David Thompson remarked on rotting carcasses on the shores of Columbia Lake!) and of the Hadley Lake (Lasqueti Island) stickleback species pair are notable examples.
BC’s freshwater fish species at risk
Recognizing the effects of the Anthropocene on BC’s native fish diversity, the Canadian Species at Risk Act (enacted in 2003) seeks to assess which species are at risk and to affect their recovery. British Columbia currently has 27 species (and several population groups within these species) that have been assessed as Extinct or at some level of risk of extinction (“Extirpated”, “Endangered”, “Threatened”, or “Special Concern”) – the second highest in number in Canada (Ontario has the most). For example, the Hadley Lake stickleback species pair has been assessed as Extinct, the Nooksack dace as Endangered, the lower Fraser River population of White Sturgeon as Threatened, and the Columbia Sculpin as Special Concern (see http://www.registrelep-sararegistry.gc.ca/species/default_e.cfm# for more information). Several salmon populations have been assessed at some level of risk as well (e.g., Okanagan Chinook salmon, Cutltus Lake sockeye salmon, Thompson River coho salmon). The principle threats to BC’s freshwater fishes are habitat loss and degradation and non-native and harmful (i.e., “invasive”) species (see Dextrase and Mandrak 2006). The BC Fish Protection Act (1997) also seeks to protect BC’s fishes and their habitats, and ongoing commitments are required by all to ensure the persistence of our unique freshwater fish fauna.
1The text herein is based heavily on the excellent reviews provided in McPhail and Carveth (1994) and McPhail (2007).
Dextrase, A. and N. Mandrak. 2006. Impacts of alien invasive species on freshwater fauna at risk in Canada. Biological Invasions 8: 13–24.
McPhail, J. D., and R. Carveth. 1994. Field key to the freshwater fishes of British Columbia. Resources Inventory Council, Province of BC.
McPhail, J. D. 2007. Freshwater fishes of British Columbia. University of Alberta Press, Edmonton.
Taylor, E.B. 2004. An analysis of homogenization and differentiation of Canadian freshwater fish faunas with an emphasis on British Columbia. Canadian. Journal of Fisheries and Aquatic Science 61: 68-79.
Eric Taylor teaches a course at the University of British Columbia on Diversity and Evolution of Fishes. Read more here.