New dietary study reveals salmon hotspots for grizzly and black bears across 700,000 square kilometres

Study: "Intrapopulation diversity in isotopic niche over landscapes: Spatial patterns inform conservation of bear–salmon systems".

A bear in Mussel Inlet.

Photo by Jamen Rhodes.

Understanding where individual animals consume critical foods can inform conservation efforts for large carnivores. A new study by scientists at Raincoast Conservation and the University of Victoria shows hotspots of salmon consumptions by bears across a huge expanse of western North America. These findings were published today in the peer-reviewed open-access journal, Ecosphere.12

Megan Adams, Raincoast scientist and PhD candidate at the University of Victoria and colleagues used a chemical technique (stable isotope analysis) to estimate salmon consumption using a massive dataset of hair samples from over 1,400 black and grizzly bears collected over 690,000 km2 of British Columbia (BC), Canada, from 1995-2014. Understanding where and how much salmon bears eat is critically important to their conservation; higher salmon consumption is associated with greater bear density and reproduction.

“Bears with high-salmon diets are often the fittest bears. We want to know where they roam and ask whether they are protected from multiple human stressors.” Megan Adams

The study showed clear patterns on a landscape scale. Salmon-bearing waterways punctuate into British Columbia over hundreds of kilometres. The authors found that grizzly bears – especially males – access this resource over 1,000 km into interior habitats.3

This study demonstrates that the bear-salmon system goes well beyond the coastal areas, including BC’s “Great Bear Rainforest” in which most people think of strong bear-salmon relationships.

In addition to spatial patterns, there are distinct differences between bear species and sexes. Grizzly bears consume much more salmon than black bears across their habitats. Black bears vary from nearly vegetarian to salmon-focused consumers. Males of both species consume far more salmon than their female counterparts.

The authors also looked at how protected areas conserve regions of particular importance. They compared patterns of salmon use by female grizzly bears, the reproductive powerhouses of populations, inside and outside of coastal protected areas. Parks contained bears with a variety of diets – from eating little to lots of fish. This means that any new protected areas could instead focus on high productivity (e.g., high salmon availability) areas.

Side by side maps of density of male and female Grizzly bears

Fig. 5. Spatial patterns of salmon consumption estimated by kernel regression in (a) female and (b) male grizzly bear (Ursus arctos horribilis) diet across British Columbia, between 1995 and 2014. Major salmon-bearing rivers are depicted as gray lines. Areas depicted in white represent regions outside of the models’ spatial extent. Histograms represent frequency of individual bears’ observed median values of proportional salmon consumption.

“Bears with high-salmon diets are often the fittest bears. We want to know where they roam and ask whether they are protected from multiple human stressors,” explains Adams. “These results demonstrate important connections between land and sea over huge landscapes. Fisheries and land-use management would benefit from integrating beyond discrete geo-political jurisdictions to take ecosystem processes into account and consider habitat protections beyond existing boundaries”.

Adams and colleagues collaborate with Indigenous resource managers as part of the Central Coast Bear Working Group. Wuikinuxv Nation’s Stewardship Director, Danielle Shaw, is one of the project’s collaborators in this network, who stresses, “The health of salmon stocks is a direct indicator of the health of an entire ecosystem. By looking at what other species need to ensure their sustenance, we are progressing towards a more ecosystem-based approach to conservation and management. We have a responsibility to ensure all other species are fed before we fill our own bellies.”

This study provides resource managers – Indigenous and Western alike – with dietary information from hundreds of bears across thousands of square kilometres, shedding light on the ecological interconnections of ecology in the expansive bear-salmon-human system in western North America.

Megan Adams in the lab.

Megan Adams, Megan Adams, Hakai-Raincoast Scholar, working in the lab. Photo by Andy Wright.

  1. From Adams, M. S., C. N. Service, A. Bateman, M. Bourbonnais, K. A. Artelle, T. Nelson, P. C. Paquet, T. Levi, and C. T. Darimont. 2017. Intrapopulation diversity in isotopic niche over landscapes: Spatial patterns inform conservation of bear–salmon systems. Ecosphere 8(6):e01843. 10.1002/ecs2.1843 http://onlinelibrary.wiley.com/wol1/doi/10.1002/ecs2.1843/full
  2. Intrapopulation diversity in isotopic niche over landscapes Ecosphere, Adams et al 2017 (PDF)
  3. See copyright-free Open Access figure: Figure 5. Spatial patterns of salmon consumption estimated (PDF).

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