Alaska Department of Fish and Game, Division of Subsistence. Subsistence and personal use harvest of salmon in Alaska, 1960-2012. Knowledge Network for Biocomplexity. doi:10.5063/F18P5XTN.

Alaska Department of Fish and Game, Division of Subsistence. 2018. Subsistence harvest information by region, community, resource, and year, 1964-2015. Knowledge Network for Biocomplexity. doi:10.5063/F1S75DNC.

By Peter Westley and Courtney Carothers

One of the most coherent and pervasive signals of climate change is the poleward shifts in species distributions and altered timing of key life history events such as spawning or migration (reviewed by Parmesan et al. 2006). In freshwaters of the continental United States, coldwater adapted salmonids have increasingly little suitable habitat owning to rapidly warming temperatures (Wenger et al. 2011). In stark contrast, ecosystems of the Arctic are only now approaching warm enough temperatures to potentially support viable self-sustaining populations of Pacific salmon (genera Oncorhynchus) or Atlantic salmon (Salmo salar). Salmon colonizing the Arctic represents a fascinating intersection of the biophysical and sociocultural aspects of the Alaska salmon system. While the biological and physical aspects related to successful salmon colonization are relatively known given our understanding of salmon ecology, the responses to salmon by the human system and the ecosystem impacts of a novel species are far from clear.

Despite a lack of compelling evidence, it is widely thought that invading Pacific salmon are likely to have negative impacts on local species established in the Arctic (Reist et al. 2006). The potential for competitive exclusion of local species such as whitefishes, Dolly Varden, lamprey, or sticklebacks seems unlikely as these species coexist throughout much of the range of Pacific salmon. Experimental and field-based work to quantify the competition between Pacific salmon (coho salmon) and Dolly Varden indicate low risk for competition as species exploited resources uniquely from one another, thereby facilitating coexistence in small streams (Dolloff and Reeves 1990). Similarly, biological interactions between local and invading salmon are unlikely to markedly impede the probability of establishment. Though once the subject of a statewide sponsored bounty based on perceptions of being a prolific predator, Dolly Varden are not major consumers of juvenile salmonids in many systems, including the Chignik region (Roos 1959).

In contrast, the weight of evidence suggests that colonizing Pacific salmon may provide beneficial subsidies to freshwater ecosystems and directly influence the growth of local fishes through the consumption of salmon eggs and flesh during the spawning season and after natural death of spawners. Where examined, the annual energy intake by species such as Dolly Varden is dwarfed by the effect of spawning salmon during a relatively short window. Indeed, the importance of the salmon subsidy is reflected in the seasonally flexible digestive capacity of Dolly Varden who ramp up their internal hardware for processing salmon eggs during the time they are available and then shrink their stomach and other organs during the winter and thereby save on energy while they wait for the next cycle of salmon nutrients (Armstrong and Bond 2013). The role of salmon-derived subsidies on freshwater growth of juvenile fishes is well known and thus it seems likely that the colonization of spawning Pacific salmon may serve to benefit local species. That being said, whether increased growth will translate to increased survival or population robustness is far less clear. Beyond the potential direct effects of growth on survival, increased growth may have life history effects for some species who migrate to sea during the summer given the greater options for foraging compared to freshwater.  If the amount of high quality food increased from salmon (e.g. salmon eggs) migrating species like Dolly Varden may alter their life history decisions to spend more of their life in freshwaters and may even forego going to the ocean all together (Bond et al. 2015).

A warming climate system and the increased suitability of freshwaters for colonizing salmon has spurred a curious biological race. Pacific salmon are expanding into the Arctic from their native North American range and from populations (particularly pink salmon) that were introduced to the Barents Sea area of Russia. At the same time, Atlantic salmon that are native to Eastern North America and Eurasia are also expanding north, leading to the potential for interactions between these species that have been geographically isolated for at least 15 million years. If one were to place a wager on the outcome of this biological race, who should be picked as a winner? To the extent that the past can predict the future, Atlantic salmon have a dismal track record of successfully colonizing habitats outside of their native range. Despite chronic releases of farmed raised Atlantic salmon in Patagonia and periodic escapes in British Columbia and the Pacific Northwest, no self sustaining populations of Atlantic salmon are currently known (Bisson 2006). That is not to say that evidence of successful reproduction by Atlantic salmon is absent as periodically the juveniles of invading parents are observed in streams of the Pacific Northwest (e.g. Volpe et al 2000). However, repeated sampling of these rivers have failed to find evidence that the population is established and generally the occurrence of juveniles disappears after a few seasons. In contrast, Pacific salmon have successfully colonized and established populations throughout the Southern Hemisphere in locales such as New Zealand (Quinn et al. 2001) and the Patagonia region of Chile and Argentina (Correa and Gross 2008). Given this track record of colonization, coupled with increased observations of Pacific salmon into the Beaufort Sea it seems that the upper hand is tipped in favor towards Oncorhynchus.

Pacific salmon are being met with a mixed reception by the indigenous traditional harvesters in the region. Through discussions with resident elder and long-time fishermen, Carothers et al. (in preparation, synthesizing Cotton 2012) relay variable opinions about perceptions regarding changes in salmon abundance in the Arctic, but consistent belief that harvests are on the rise. The perception of the benefits of increased salmon harvests likewise varied among local experts. Several fishermen spoke detrimentally about the numbers of pink salmon being caught that have “gotten to the point where there’s too many pinks to deal with” and another noted “we get more of the humpies (pink salmon), a lot of the humpies, and the last two years there’s been mostly humpies”. Given that pink salmon deteriorate in quality very quickly as they approach sexually maturity it is understandable that these increases in pink salmon harvests are not view favorably. In contrast, informants from both Utqiaġvik and Nuiqsut report to being considered lucky if they catch one or two Chinook salmon over the course of the season.

Table 1