J.D. McPhail. 1998. Fishes in Smith, I.M., and G.G.E. Scudder, eds. Assessment of species diversity in the Montane Cordillera Ecozone. Burlington: Ecological Monitoring and Assessment Network, 1998.

FISHES

J.D. McPhail
Department of Zoology
University of British Columbia
Vancouver, B.C.
V6T 1Z4

ABSTRACT

Seven major drainage systems rise in the Canadian Montane Ecozone (MCE). Although each of these systems contains a different mix of species, in aggregate 59 species of freshwater fish occur within the ecozone. Of these, 43 species (73%) are native and 16 (23%) are introduced. Four of the native species are listed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) --- the white sturgeon, Acipenser transmontanus; the speckled dace, Rhinichthys osculus, and the Umatilla dace, Rhinichthys umatilla, are listed as vulnerable while the shorthead sculpin, Cottus confusus, is listed as threatened. All of the native species are postglacial immigrants from regions outside the boundaries of the MCE. The majority (74%) of these immigrants survived glaciation in either the Pacific (24 species) or Great Plains (8 species) refugia, but at least 11 species survived in more than one ice-free region. Typically, fish that survived glaciation in multiple refugia diverged genetically after their interglacial distributions were fragmented by ice. Consequently, many of these species carry genetic markers that are diagnostic for the different refugia and, in some species, there are life-history differences between populations that originated in different refugia. Although these different forms of widespread species have no formal taxonomic status, they are an important component of the biodiversity of fishes in the Canadian Montane Ecozone.

In addition to divergences that date to the beginning of the last (Wisconsinan) glaciation, recent (postglacial) divergences also have contributed to the biodiversity of the MCE. In many areas, the land was depressed under the weight of glacial ice but after a brief time lag the land rebounded when the glaciers withdrew. Differential isostatic rebound created impassable barriers on many rivers and streams, and isolated fish populations above these barriers. Typically, species diversity above such barriers is low, but above-barrier populations often are genetically differentiated from below-barrier populations of the same species. Similarly, many populations of anadromous fish (e.g., sockeye salmon, Oncorhynchus nerka) have diverged postglacially into migratory and non-migratory populations. An important aspect of these postglacial divergences is parallel evolution - the repeated, but independent, evolution of similar morphologies and behaviours under similar ecological and physical conditions.

The distribution and abundance of species within the ecozone is not static and in the past has changed in response to both natural and anthropogenic alterations in the environment. For example, the present distribution within the ecozone of the chiselmouth, Acrocheilus alutaceus, consists of a small number of widely scattered populations. A plausible explanation for these disjunct populations is that they are remnants of a once wider distribution that was achieved during the warmer postglacial hypsithermal period. In a tectonically active region like the Canadian Montane Ecozone, another source of natural changes in distribution are stream captures. An example is the distribution of the Dolly Varden (Salvelinus malma). In one small area this coastal species has crossed by a series of head- stream captures from the Skeena system into the adjacent headwaters of both the upper Fraser and upper Peace systems.

A wide variety of human activites have altered the distribution and abundance of the native fish fauna of the Canadian Montane Ecozone. Resource extraction industries such as mining and forestry have had widespread, but often local, impacts on fish biodiversity. Although local, these impacts can be serious. For example, the one fish species in this ecozone listed as threatened by COSEWIC is the shorthead sculpin. Except for a population in the St. Mary River, Alberta, and a few questionable populations in Columbia tributaries near Trail, B.C., the only unquestioned populations of shorthead sculpin in the MCE are in the lower Flathead River --- an area scheduled for the development of open-pit coal mines. The fishing industries (commercial and recreational) have also damaged biodiversity in this ecozone. Some salmonid stocks have been lost through over-exploitation, but the greatest threats to biodiversity are the attempts to "improve" on nature. For example, massive salmonid enhancement programs have artificially inflated some Pacific salmon stocks to the serious detriment of less numerous wild stocks and other fish species that happen to migrate through the fishery at the same time as the enhanced stocks. Additionally, hundreds, if not thousands, of lakes in the MCE have been stocked with domesticated strains of rainbow trout (a native species). We probably will never know how many of these stockings destroyed, or genetically altered, indigenous trout populations. Although many of the stocked lakes originally did not contain fish, they did contain invertebrate faunas that were altered by the introduction of fish. The deliberate introduction of exotic (non-native) species was. another widespread attempt to improve on nature. Fortunately, most of these introduced species are not widely distributed and are only abundant in altered habitats. Nonetheless it is ironic that in an ecozone that is often viewed as almost pristine approximately a quarter of the fish species present in the region are exotics. Translocations --- the introduction of native species into waters where they originally did not occur --- have had more serious impacts on biodiversity thatn the introduction of exotics. Rainbow trout introduced into lakes and streams originally occupied by westslope cutthroat trout (Oncorhynchus clarki lewisi) have led to the loss of populations through displacement by the more aggressive rainbow trout and through hybridization. The bull trout (Salvelinus confluentus) is the only fish species in British Columbia officially recognized as wildlife under the B.C. Forest Practices Code, and is listed by both B.C. and Alberta as a species of special concern. In the Cordilleran National Parks, bull trout are now extinct in a number of lakes where lake trout (Salvelinus namaycush) were introduced to "improve" recreational fishing.

Reproductive isolation in many freshwater fish is maintained by subtle differences in spawning habitats or spawning times. If these factors are altered, reproductive isolation can break down and this results in hybridization and, sometimes, in introgression. Impoundments (hydroelectric and storage) produce extensive changes in aquatic environments and this often results in the break-down of reproductive isolation between some species. Urbanization, with its associated problems of eutrophication, pollution, transportation corridors, and flood control, is not a major factor in most of the MCE; however, in the south Okanagan and Kamloops regions the impacts of urban expansion probably represent the most a serious threat faced by aquatic environments.

In the past, humans have had profound, but often local, negative effects on the fish fauna of the Canadian Montane Cordillera Ecozone. At first glance, the future looks brighter. This is because changing public attitudes towards the environment and conservation have forced government agencies to modify their policies. In British Columbia, the indiscriminate stocking of domesticated trout has been replaced with a wild fish policy that encourages the conservation of wild trout and attempts to protect them from genetic contamination by hatchery stocks. Also, lake "rehabilitation" --- a euphemism for poisoning lakes to remove “coarse” fish was once a widely used management technique. Now, the public would not condone such a wholesale slaughter and, as a result, fisheries managers are reluctant to poison lakes. Also, provincial fisheries managers are now more apt to interpret their conservation obligations to include all native species and not just salmonids. Moreover, provincial agencies now employ "non-game" or native species biologists, and are actively attempting to restore urban streams and watersheds damaged by past forestry practices. Perhaps, sometime in the next century these enlightened attitudes will spread to their colleagues in the Department of Fisheries and Oceans.

Unfortunately, public concern for the environment and biodiversity appears to be waning as the economy slows. For example, in British Columbia, the Forest Practices Code is being "revised" and the Fish Protection Act is under assault by the agricultural industry and land developers. If this trend continues, the future of aquatic biodiversity in the MCE does not look bright.

 

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