Established in North America, but not including the Great Lakes. Oncorhynchus keta has a moderate probability of establishment if introduced to the Great Lakes (Confidence level: High).
The native ranges of Oncorhynchus keta have similar climatic conditions as the Great Lakes. Oncorhynchus keta can tolerate a broad range of salinity and survive abrupt changes in salinity (Clarke and Hirano 2010). Optimal water temperatures for Oncorhynchus keta are between 5-27°C (Hale et al. 1985). This species experiences high mortality when dissolved oxygen drops below 2 mg/L.
Oncorhynchus keta is capable of surviving winter temperature in the Great Lakes, but its ability to overwinter is limited by its oxygen requirements. There are populations of Oncorhynchus keta that overwinter in the North Pacific, the Gulf of Alaska, and the Bering Sea (Urawa et al. 2004), usually in waters that are 4-6°C. During homing migration, chum salmon make vertical diel movements to deeper waters to feed, experiencing temperatures under 5°C regularly (Azumaya et al. 2005). Although chum salmon can tolerate such low temperatures, it may not be able to for long periods of time, and behaviorally avoids them by moving to shallower waters periodically.
Oncorhynchus keta opportunistically feeds on zooplankton, invertebrates, mollusks, and fishes, and has a relatively broad diet compared to other Oncorhynchus species (Behnke 2010, Kaeriyama et al. 2004). The chum salmon fry feed on small invertebrates as they migrate downstream and on crustaceans as they move into estuaries. Oncorhynchus keta will likely find an appropriate food source if introduced to the Great Lakes. Alewife, Alosa pseudoharengus, is an established nonindigenous species in the Great Lakes and may provide a food source for introduced salmon (Crawford 2001), such as Oncorhynchus keta.
For successful reproduction, chum salmon require loose streambed gravel to lay their eggs (Bakkala 1970). Chum salmon migrate upstream to rivers to spawn, can reproduce successfully in intertidal zones at the mouth of streams (Behnke 2010) and in lakes with upwelling groundwater (Wilson 2006). Chum salmon migrate upstream to spawn at temperatures under 15°C and dissolved oxygen levels greater than 6.3 mg/L (Hale et al. 1985). They have been observed migrating upstream in waters that are as low as 4.4°C, and temperatures above 25.5°C are lethal. The chum salmon fry prefer temperatures of 12-14°C, and have lethal water temperature limits above 23.8°C and below -0.1°C (Brett and Alderdice 1958). Chum fry undergoes developmental changes for life in sea water, and migration to sea water within the first summer is necessary for survival (Hale et al. 1985); however, chum salmon have been reared to maturity in freshwater in captivity (R.L. Burgner, Fisheries Research Institute, University of Washington, Seattle, Washington, pers. comm. In Salo 1991).
Previous introductions of Onchorhynchus keta to the Great Lakes did not result in the establishment of self-sustaining populations (Crawford 2001, MacCrimmon 1977). It was also introduced to the Gulf of Riga, in the bay of the Baltic Sea, but has only been found in small numbers (Ojaveer 1995). Oncorhynchus keta is predicted by Kolar and Lodge (2002) to be intentionally introduced to the Great Lakes for the purpose of aquaculture or sport, and to spread at a fast rate if introduced. Although Kolar and Lodge (2002) predict high probability of establishment and spread, the history of this species in the Great Lakes, which includes nearly 40 years of stocking, suggest that some unknown factors prevent its establishment in the Great Lakes region.
There have been several studies conducted on how climate change affects chum salmon, but none have predicted how climate change in the Great Lakes may impact chum salmon establishment. In the subarctic North Pacific, increased chum fingerling growth rates correlated with increased zooplankton biomass as a result of climate change in the late 1980s (Seo et al. 2006). In the Gulf of Alaska, chum salmon diets switched from one dominated by gelatinous zooplankton to one with greater diversity of zooplankton species due to climate alterations caused by El Niño and La Niña events (Kaeriyama et al. 2004). Models developed by Harvey et al. (2012) predict that chum salmon post-spawning carcasses will decompose at a faster rate due to warming and climate change. Chum salmon are a major component of overwintering bald eagle diets in the Puget Sound, and faster carcass decomposition rate may decrease the biomass of carcasses available for the bald eagles. The effects of climate change such as warmer water temperatures and shorter duration of ice cover may aid the establishment of Oncorhynchus keta and enable it to overwinter in the Great Lakes. Chum salmon fry require migration to seawater (Hale et al. 1985), so increased salinization may increase their survival in the Great Lakes.
This species may be vulnerable to habitat degradation. Chum salmon populations that spawned in the Columbia River basin had declined by the 1950s (Behnke 2010). The spawning habitat quality was degraded by upstream logging, pollution and water diversions, resulting in spawns of 1,000 to 5,000 fish. By 2011, spawning runs had attained 10,000 fish for the first time in 46 years after the implementation of habitat protection and enhancement.