Salmon: A Keystone Species

The enormous benefit that salmon provide for countless species and the overall health and function of the coast is what makes salmon a keystone species.

As salmon disappear, coastal ecosystems, culture and economies are disproportionately impacted. The enormous benefit that salmon provide for countless species and the overall health and function of the coast is what makes salmon a keystone species — an integral species which ecosystems depend on, with drastic changes resulting if they are removed. Each part of a salmon’s life cycle is heavily interconnected with its surrounding environment.

salmon feed our coast

land mammals

birds

marine mammals

forests

Pacific salmon are mostly anadromous, meaning they are born in freshwater, migrate to the ocean, and then migrate back to freshwater, spawn and die immediately after. On their journey to the ocean, more than 50 per cent of their diet is insects which fall into streams from surrounding tree canopies (Allan et al. 2003, Baxter et al. 2005). Without Pacific salmon, there would be the potential for an explosion of insects, as salmon are the main insect predator in aquatic environments. When salmon return to their native streams to spawn, their energy-rich carcasses and eggs are consumed by a variety of predators in coastal watersheds, including wolves, bears, and scavenging birds. In some cases, the diets of wolves can consist of almost 50 per cent salmon, with the rest made up of small animals in their ecosystems (Stankey et al. 2017). Coastal wolves are only one of many species that have uniquely co-evolved alongside wild salmon over millennia.

Salmon support populations of eagles, gulls, sea birds and more by providing them with nutrients essential for overwinter survival and migrations. The amount of salmon in a stream has been shown to be an indicator of the density and diversity in species of birds in the surrounding ecosystem (Field and Reynolds 2012). Pacific salmon populations are important for the survival of diverse and large assemblages of resident and migratory birds, and their disappearance would mean the decline of many bird species (Field and Reynolds 2012).

In areas where salmon are abundant, bears will eat up an average of 15 salmon per day, a significant portion of their diet

Salmon are an important source of nutrients for bears in coastal watersheds as well. The population density of bears can be up to 20 times greater in areas where salmon are abundant, versus areas where they do not occur (Reimchen 2000). In areas where salmon are abundant, bears will eat an average of 15 salmon per day, a significant portion of their diet (Reimchen 2000). Coastal bears get from 33-94 per cent of their annual protein from salmon through scavenging for dead carcasses and capturing them in streams (Klinka and Reimchen 2009). Without salmon as a food source, populations of bears would become severely at-risk.

Salmon play a significant role in the survival of certain ocean species during their time in salt water. For example, the Chinook salmon are the primary prey for the southern resident killer whale. In the past 35 years, consumption of salmon by killer whales and seals has increased by over 25 million individual salmon, while harvest of the fish has increased despite reduction by fisheries in an attempt to recover endangered killer whales (Chasco et al. 2017). If populations of Chinook salmon continue to decline, there will be major correlating impacts on the food web. Some predict that certain apex predators like the southern resident killer whale will become extinct.

When salmon die at the end of their life cycle, their carcasses provide valuable nutrients to streams and rivers, providing a significant increase in organic matter and nutrients which is believed to enhance the productivity of the surrounding ecosystem (Holtgrieve and Schindler 2011). These nutrients are transferred to all levels of the food chain, and in some cases, species adjust their survival strategies to capitalize on the additional resources (Holtgrieve and Schindler 2011). Throughout their life cycle, salmon fundamentally transform the way ecosystems function, by playing the roles of both predator and prey, plus releasing important nutrients back in the ecosystem after they spawn.

Works Cited

  • Allan, J. D., M. S. Wipfli, J. P.Caouette, and A. Prussian. 2003. Influence of streamside vegetation on inputs of terrestrial invertebrates to salmonid food webs. Canadian Journal of Fisheries and Aquatic Sciences 60: 309-320.
  • Baxter, C. V. , K. D. Fausch, and W. C. Saunders. 2005. Tangled webs: reciprocal flows of invertebrate prey link streams and riparian zones. Freshwater Biology 50: 201-220.
  • Chasco, E. B., Kaplan, C. I., Thomas, C. A., and Acevedo-Gutierrez, A. (2017). Competing tradeoffs between increasing marine mammal predation and fisheries harvest of Chinook salmon. Scientific Reports, 7: 1-14.
  • Field, R. D., and Reynolds, J. D. (2012). Ecological links between salmon, large carnivore predation, and scavenging birds. Journal of Avian Biology, 44: 9-16.
  • Holtgrieve, G. W., and Schindler, D. E. (2011). Marine-derived nutrients, bioturbation, and ecosystem metabolism: reconsidering the role of salmon in streams. Ecological Society of America, 92: 373-385.
  • Klinka, D. R., and Reimchen, T. E. (2009). Darkness, Twilight, and Daylight Foraging Success of Bears (Ursus americanus) on Salmon in Coastal British Columbia. American Society of Mammalogists, 90: 144-149.
  • Reimchen, T. E. (2000). Some ecological and evolutionary aspects of bear-salmon interactions in coastal British Columbia. Canadian Journal of Zoology, 78: 448-457.
  • Stanek, A. E., Wolf, N., Hilderbrand, G. V., and Mangipane, B. (2017). Seasonal foraging strategies of Alaskan gray wolves ( Canis lupus) in an ecosystem subsidized by Pacific salmon ( Oncorhynchus spp.). Canadian Journal of Zoology, 95: 555-563.
  • Williams, R., Krkosek, M., Ashe, E., and Branch, T. A. (2011). Competing conservation objectives for predators and prey: Estimating killer whale prey requirements for chinook salmon. PLoS One, 6: 1-9.

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