The scientific background and the aim of the project standing of the mechanisms influencing the distribution and abundance of animals and plants, how these organisms change at their species border, and how they cope with interspecific interactions and/or adapt to new environmental conditions are major goals of classic ecology, biogeography, and evolutionary ecology. In order to identify such processes we need to examine unexploited populations of species living at their distributional border. Among salmonid fishes, such populations are today restricted to the Arctic, where Arctic and Dolly Varden chars, known as the salvelinus alpinus species complex, commonly inhabit lakes and rivers as mono-species stocks. Whereas Dolly Varden tend to be restricted to the Pacific and Western Arctic, Arctic char has a wider circumpolar distribution. Both taxa occur as sea-run (anadromous), stream resident and/or landlocked forms. The Arctic char is extremely sensitive to abiotic as well as biotic changes in its environment, thus clearly illustrating its niche borders, and also various changes occurring in its environment (Hammar 1998).

Its extensive geographic range together with its vital economic value and vulnerability, highlight the Arctic char as a relevant indicator for studies of environmental changes in northern regions, and thus also for supervision of the sustainable use of such ecosystems. The production of this diverse salmonid is confined by a number of restraints, and its habitat is highly susceptible, reacting explicitly to environmental changes. As a consequence, numerous populations of Arctic char are now demonstrating serious signs of over-exploitation, and the extinction rate at lower latitudes during the last century has been dramatic. Information from unexploited populations is thus also of the utmost importance for conservation measures, management and a sustainable harvest programme of Arctic and Dolly Varden char in southern as well as northern areas.

This cruise report provides the first assessment of freshwater fish catches made during Tundra Northwest 1999 within the project entitled: The Salvelinus alpinus species complex; distribution, biodiversity, and ecology of Arctic and Dolly Varden chars across the Canadian Arctic. The project is an extension of ongoing studies on the biodiversity of chars being carried out in the European Arctic, Scandinavia, Scotland, Greenland, Eastern and Arctic Canada, Alaska and Russia in collaboration with colleagues from the numerous countries involved.

In short, the project aims at documenting the diversity of fish species in freshwater systems throughout the Canadian Arctic. In lakes or streams where only char are present our objectives in particular include collecting information on intraspecific interactions and the structural composition of populations, cataloguing the ecological and genetic diversity of alternate life history strategies and extending the present knowledge of the geographic genetic pattern recognized in the distribution of the Salvelinus alpinus – S. malma complex. In collaboration with other research projects of Tundra Northwest 1999, the present project will also provide samples of char tissue, preferably with a resident life history, taken from different geographical regions for environmental pollutant monitoring at various institutes, and whole preserved specimens for natural museum collections in Sweden and Canada.

Arctic char and the diversity of Arctic freshwater fish communities

Due to its extensive geographic range, its extreme ecological and phenotypic plasticity, the Arctic char is treated as a series of taxa at different taxonomic levels within the Salvelinus alpinus species complex. Because of incomplete sexual barriers, the borders between these biological species, and also more commonly accepted Linnéan species, are weak. The speciation processes include repeated isolating processes, as well as introgression during interglacial periods. The methods of systematic characterization and monitoring vary from morphological and meristic characters to genetic analyses of DNA and single genes (e.g., Reist 1989, Reist et al. 1995).

The niche of an allopatric char population is exceptionally wide and different functions of the fish community seem to be carried out by individuals belonging to the same gene pool. Unexploited populations commonly demonstrate sigmoid growth and bimodal size-structure (Johnson 1983). Between modal concentrations of small and large individuals, the low occurrence of medium-sized individuals seems to represent a fast transition stage, among sea-run char known as smoltification. Among landlocked populations of Arctic char, a similar stage illustrates the transition of selected individuals in to cannibalism, and in extreme cases the upper modal group of cannibals tends to dominate and structure the population (Hammar 1998).

In a major part of their range Arctic char perform seasonal feeding migrations to the sea. Overwintering and spawning, however, always take place in freshwater. In landlocked cases, the population has become cut off from the sea by complete obstructions such as waterfalls or by the presence of various biological filters, such as the presence of other species. The rivers draining in to the Canadian Arctic do in fact extend the distribution of various southern fish species in to the Arctic region, and lake trout (Salvelinus namaycush), various coregonids (Coregonus spp.), fourhorn sculpin (Triglopsis quadricornis), threespine (Gasterosteus aculeatus) and/or ninespine sticklebacks (Pungitius pungitius) are known to occur in lakes along the mainland coast, southern Banks and on Victoria and Baffin Islands (Scott and Crossman 1973). With the possible exception of lake trout, all the listed species tolerate increased salinity, and may thus also occur in coastal water, a crucial mechanism for further dispersal in to the Arctic.

Methods

Alternative freshwater bodies likely to contain landlocked Arctic char with in each of the originally approved science-sites were chosen from detailed studies of available maps. At each site, one and occasionally two lakes were sampled with gillnets, set from an inflatable Zodiac operated with an outboard engine. The design of the ecological test fishing programme using Lundgren’s multiple mesh size gillnets (10-75 mm), has been described previously for similar studies in e.g., insular Newfoundland and Labrador (Hammar and Filipsson 1985). The gillnets were set for varying lengths of time during the darkest period. The number of gillnets and thus the number of fish caught in each lake was kept to a minimum for strong reasons of conservation, and also to avoid exceeding the bag limits specified in our permits.

After being measured for length (maximum total length and fork length) and weight, each fish was frozen individually and stored until sampled for further analyses later in a laboratory. These analyses include ecological, morphometric, meristic, as well as genetic analyses at single gene and molecular levels. In addition, tissue will be sampled for environmental pollutants (Berglund et al.).

Preliminary results and early reflections

With the exception of Raddi Lake on Banks Island, and two lakes sampled in Ivvavik National park, the remaining lakes have most likely never been gillnetted, nor ha d their fish documented and sampled previously for scientific purposes. The results thus include novel information on the geographic distribution of a series of fish species in the Canadian Arctic. As the preferred alpine lakes with landlocked char tended to be located further inland from the coastal planes dominating most sites, they were frequently regarded as too distant in relation to the location of the icebreaker and the sites of other projects more devoted to the coastal tundra ecology. Most lakes surveyed thus had outlet streams without obstructions to migratory stocks, or were even too shallow to contain fish at all.

Based on the external appearance of the Arctic char, the preliminary identification of life history affiliation suggests a numeric dominance of anadromous char in the samples. Landlocked populations were only suspected in two lakes in Ivvavik National park, and in southeast Baffin Island. Among the anadromous populations, however, the old and large-sized char sampled in a temporarily closed lake on Melville Island may in fact comprise originally sea-run char that have reversed their life history and retired as resident. This northern lake also contained a dense population of small-sized fourhorn sculpin; a glacial relict which no doubt may be exploited as prey by these possibly piscivorous char. Besides occurring in the canyon lake in Albert Bay, where the catch indicates the population to be allopatric, lake trout were also recorded in sympatry with anadromous Arctic char at the sites in the south of Victoria and Banks Islands. In the latter lake the catch also included 2-3 taxa of coregonids, possibly two populations of whitefish, and a smaller deep-living cisco. Among the species known to inhabit the region, the sampled coregonids probably consist of broad whitefish (Coregonus nasus), lake whitefish (C. clupeaformis) and least cisco (C. sardinella). Finally, ninespine stickleback were recorded in lakes and tributaries at most mainland sites, and on Victoria and Banks Islands.

Size structure differed among the species and the populations, very much influenced by the presence and dominance of predators/cannibals. In contrast to the bimodal size-structure recorded in most char populations with an upper modal group of ca 40-60 cm, the lake trout populations expressed a monomodal structure with fish concentrated around this size. Because of the failure to sample extreme landlocked  populations with a dominance of large cannibalistic individuals, young premigratory individuals from geographically scattered anadromous stocks were selected instead for pollutant analyses. Also subsamples of larger individuals from a series of anadromous populations have been selected for specific studies illustrating a life history mediated shift in the quality and quantity of environmental pollutants. All specimens of lake trout and whitefish caught on rod, and most of the gillnetted ninespine stickleback and fourhorn sculpin were preserved for the Museum of Natural History in Stockholm.