Non‐stationary and interactive effects of climate and competition on pink salmon productivity

Abstract

Pacific salmon (Oncorhynchus spp.) are exposed to increased environmental change and multiple human stressors. To anticipate future impacts of global change and to improve sustainable resource management, it is critical to understand how wild salmon populations respond to stressors associated with human-caused changes such as climate warming and ocean acidification, as well as competition in the ocean, which is intensified by the large-scale production and release of hatchery reared salmon. Pink salmon (O. gorbuscha) are a keystone species in the North Pacific Ocean and support highly valuable commercial fisheries. We investigated the joint effects of changes in ocean conditions and salmon abundances on the productivity of wild pink salmon. Our analysis focused on Prince William Sound in Alaska, because the region accounts for ~50% of the global production of hatchery pink salmon with local hatcheries releasing 600-700 million pink salmon fry annually. Using 60 years of data on wild pink salmon abundances, hatchery releases, and ecological conditions in the ocean, we find evidence that hatchery pink salmon releases negatively affect wild pink salmon productivity, likely through competition between wild and hatchery juveniles in nearshore marine habitats. We find no evidence for effects of ocean acidification on pink salmon productivity. However, a change in the leading mode of North Pacific climate in 1988-1989 weakened the temperature-productivity relationship and altered the strength of intraspecific density dependence. Therefore, our results suggest non-stationary (i.e., time varying) and interactive effects of ocean climate and competition on pink salmon productivity. Our findings further highlight the need for salmon management to consider potential adverse effects of large-scale hatchery production within the context of ocean change.

Reduced relative fitness in hatchery‐origin Pink Salmon in two streams in Prince William Sound, Alaska

“…More recent analyses suggest that hatchery releases diminish the productivity of wild stocks of Pink Salmon to PWS (Amoroso et al, 2017;Ohlberger et al, 2022), despite recent record wild-stock returns in the odd-year lineage (Haught et al, 2017;Knudsen et al, 2021).…”

Warming climate impacts on production dynamics of southern populations of Pacific salmon in the North Pacific Ocean

“…Non‐stationary relationships among physical and biological variables are thought to be the effects of environmental conditions, such as temperature, on population processes, such as recruitment, and can vary in intensity and/or direction over time (Ohlberger et al, 2022). Pacific salmon productivity increased after the 1976–1977 climate regime shift in the North Pacific Ocean (Figure 3).…”

“…The effects of global warming on Pacific salmon production have been studied in freshwater (Bryant, 2009;Zang et al, 2019) and oceanic ecosystems (Kaeriyama, 2008;Kaeriyama et al, 2014;Mantua, 2009;Ohlberger et al, 2022;Yati et al, 2020). Thus, the potential effects of global warming on the oceanic distribution of chum salmon in the North Pacific and Arctic Ocean were evaluated based on the A1B scenario, that is, with medium greenhouse gas emissions in the Fourth Assessment Report of the IPCC (IPCC, 2007); based on the results, the following outcomes are predicted: (1) the distribution area of chum salmon will move from south to north in the North Pacific Ocean; (2) the migration area in the winter may shift from the Gulf of Alaska to the Western Subarctic Gyre; and (3) in southern distribution areas such as Japan, juveniles will be not able to spend adequate time to attain sufficient growth in coastal waters (Kaeriyama, 2008).…”

“…Results of the Lotka-Volterra competition model between Japanese chum salmon and Russian salmon indicate the following (Figure 8): (1) Japanese chum salmon are often losers to Russian pink salmon and winners to Russian sockeye salmon; (2) compared with Russian chum salmon, Japanese chum salmon were the winners when the population size was large owing to positive effects of global warming but were losers when global warming progressed further and negatively affected the decline of their abundance in the 2010s. Inter-and intra-specific interactions of Pacific salmon are not necessarily fixed and may change depending on environmental conditions(Ohlberger et al, 2022;Yati et al, 2020) and fluctuations in salmon biomass.…”

Watershed hydrogeomorphology drives freshwater productivity of anadromous salmonids: Implications for habitat conservation and restoration

“…The declines in anadromous salmonid abundance can be explained by several anthropogenic activities (Gillson et al, 2022;Thorstad et al, 2021). For example, the hatchery programs that have been conducted around the world for the conservation and enhancement of salmonids (Kitada, 2018(Kitada, , 2020Laikre et al, 2010;Morita, Saito, et al, 2006;Naish et al, 2007) negatively affect salmonid population persistence by decreasing fitness and reproductive success and increasing competition between fish of wild and hatchery origin (Araki et al, 2007;Christie et al, 2012;Ohlberger et al, 2022;O'Sullivan et al, 2020;Terui et al, in press;Willoughby & Christie, 2019). Moreover, the natural reproduction of anadromous salmonids has been hindered by habitat fragmentation (Hilborn, 2013;Limburg & Waldman, 2009;Nakamura & Komiyama, 2010;Watz et al, 2022).…”