Density‐dependent marine survival of hatchery‐origin Chinook salmon may be associated with pink salmon

Recovering small, endangered populations is challenging, especially if the drivers of declines are not well understood. While infrequent births and deaths may be important to the outlook of endangered populations, small sample sizes confound studies seeking the mechanisms underlying demographic fluctuations. Individual metrics of health, such as nutritive condition, can provide a rich data source on population status and may translate into population trends. We examined interannual changes in body condition metrics of endangered Southern Resident killer whales (SRKW) collected using helicopters and remotely operated drones. We imaged and measured the condition of the majority of all three social pods (J, K, and L) in each of seven years between 2008 and 2019. We used Bayesian multi‐state transition models to identify relationships between body condition changes and both tributary‐specific and area‐based indices of Chinook salmon abundance, and K‐fold cross‐validation to compare the predictive power of candidate salmon covariates. We found that Fraser River (tributary‐specific) and Salish Sea (area‐based) Chinook salmon abundances had the greatest predictive power for J Pod body condition changes, as well as the strongest relationships between any salmon covariates and SRKW condition across pods. Puget Sound (tributary‐specific) Chinook salmon abundance had the greatest predictive power for L Pod body condition changes, but a weaker relationship than Fraser River or Salish Sea abundance had with J Pod body condition. The best‐fit model for K Pod included no Chinook covariates. In addition, we found elevated mortality probabilities in SRKW exhibiting poor body condition (reflecting depleted fat reserves), 2–3 times higher than whales in more robust condition. Collectively, these findings demonstrate that (1) fluctuations in SRKW body condition can in some cases be linked to Chinook salmon abundance; (2) the three SRKW pods appear to have distinct patterns of body condition fluctuations, suggesting different foraging patterns; and (3) aerial photogrammetry is a useful early‐warning system that can identify SRKW at higher risk of mortality in the near future.

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“…2019, Kendall et al. 2020), and climate change (Crozier et al. 2008) all present substantial threats to Fraser River Chinook abundance.…”

Section: Discussionmentioning

confidence: 99%

Survival of the fattest: linking body condition to prey availability and survivorship of killer whales

et al. 2021

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“…For example, research in Puget Sound, WA, indicates negative density dependence between hatchery and natural origin fish in marine and freshwater life stages (Kendall et al., 2020). However, research investigating hatchery and natural origin fish interactions is often conducted on a local or regional scale and does not fit into the scope of our model (Kendall et al., 2020; Nelson et al., 2019). Including hatchery and natural origin stock density dependence will be an important avenue for future work, especially as some West Coast states propose to increase hatchery production (WA State Orca Task Force).…”

Section: Discussionmentioning

confidence: 99%

“…This practice artificially augments salmon abundance by producing and releasing large numbers of young salmon into rivers or estuaries; this has significant impacts to the Pacific Salmon ecosystem. For example, research in Puget Sound, WA, indicates negative density dependence between hatchery and natural origin fish in marine and freshwater life stages (Kendall et al., 2020). However, research investigating hatchery and natural origin fish interactions is often conducted on a local or regional scale and does not fit into the scope of our model (Kendall et al., 2020; Nelson et al., 2019).…”

Section: Discussionmentioning

confidence: 99%

Synchrony erodes spatial portfolios of an anadromous fish and alters availability for resource users

Sullaway

Shelton

Samhouri

2021

Journal of Animal Ecology

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1. Environmental forces can create spatially synchronous dynamics among nearby populations. However, increased climate variability, driven by anthropogenic climate change, will likely enhance synchrony among spatially disparate populations.Population synchrony may lead to greater fluctuations in abundance, but the consequences of population synchrony across multiple scales of biological organization, including impacts to putative competitors, dependent predators or human communities, are rarely considered in this context. Chinook salmon Oncorhynchus tshawytscha stocks distribute across the NortheastPacific, creating spatially variable portfolios that support large ocean fisheries and marine mammal predators, such as killer whales Orcinus orca. We rely on a multi-population model that simulates Chinook salmon ocean distribution and abundance to understand spatial portfolios, or variability in abundance within and among ocean distribution regions, of Chinook salmon stocks across 17 ocean regions from Southeast Alaska to California.3. We found the expected positive correlation between the number of stocks in an ocean region and spatial portfolio strength; however, increased demographic synchrony eroded Chinook salmon spatial portfolios in the ocean. Moreover, we observed decreased resource availability within ocean fishery management jurisdictions but not within killer whale summer habitat. We found a strong portfolio effect across both Southern Resident and Northern Resident killer whale habitats that was relatively unaffected by increased demographic synchrony, likely a result of the large spatial area included in these habitats. However, within the areas of smaller fishing management jurisdictions we found a weakening of Chinook salmon portfolios and increased but inconsistent likelihood of low abundance years as demographic synchrony increased.4. We suggest that management and conservation actions that reduce spatial synchrony can enhance short-term ecosystem resilience by promoting the stabilizing effect multiple stocks have on aggregate Chinook salmon populations and overall resource availability.

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“…The majority of hatchery produced pink salmon originate in the state of Alaska, where they were used in the 1970s as a management tool to supplement low abundances of wild populations. Pink salmon have trophic impacts on marine ecosystem components, including phytoplankton and zooplankton (Batten et al, 2018 ; Shiomoto et al, 1997 ), other salmonids (Cline et al, 2019 ; Kendall et al, 2020 ; Ruggerone & Connors, 2015 ; Ruggerone & Nielsen, 2004 ), and predators such as seabirds (Springer & van Vliet, 2014 ; Springer et al, 2018 ; Toge et al, 2011 ). While pink salmon are considered a keystone species in the North Pacific due to their broad impacts on other organisms, less is known about factors that limit population productivity and abundance of pink salmon.…”

Section: Introductionmentioning

confidence: 99%

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

Ohlberger

Ward

Brenner

et al. 2021

Global Change Biology

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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.

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Density‐dependent marine survival of hatchery‐origin Chinook salmon may be associated with pink salmon

Cited by 16 publications

References 77 publications

Survival of the fattest: linking body condition to prey availability and survivorship of killer whales

Survival of the fattest: linking body condition to prey availability and survivorship of killer whales

Synchrony erodes spatial portfolios of an anadromous fish and alters availability for resource users

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

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