New research shows how human disturbance keeps grizzlies from their salmon

Published in the journal Ecology & Evolution, a new paper titled “Human disturbance in riparian areas disrupts predator-prey interactions between grizzly bears and salmon” finds that human activity in valley bottoms dramatically reduces the amount of salmon grizzlies eat in a year, and is more influential than how much salmon is present in watersheds. 

Led by Dr. Megan Adams from the University of Victoria and Raincoast Conservation Foundation, the research team investigated how much salmon 226 individual bears consumed across 22 salmon-bearing watersheds, spanning 88,000 km² throughout British Columbia. Her team measured salmon consumption by bears using chemical tracers in grizzly bear hair samples collected between 1995 and 2014. 

The findings carry significant implications for bears and ecosystems. Grizzly bears exhibited a substantial reduction (up to 59% for females) in salmon consumption in the presence of even low levels of human footprint in salmon-bearing watersheds. This could lead to reduced litter sizes and population densities. And whether by reduced salmon foraging or fewer bears, the role of bears as vectors that distribute salmon remains into riparian forests would be reduced.

The study suggests that bears may avoid seeking such key foods if perceived risks from human activity, comprised primarily of industrial resource extraction, are too high.

“Valley bottoms are very important travel corridors and foraging locations for bears but these are spaces where human disturbance is also generally concentrated. We need to consider how our activities – whether that be valley-bottom landscape alteration or the harvesting of salmon in the ocean, hundreds of kilometers away from spawning grounds – might impact the foundational bear-salmon ecological interaction.”

Dr. Megan Adams

The new information is timely, given opportunities exist for Indigenous and provincial government agencies to integrate findings into ecosystem-based management and cumulative effects assessments. The research revealed that existing provincial riparian management regulations designed to protect salmon and their habitats were insufficient to mitigate this disturbance. Regulations at larger spatial scales , as well as introducing temporal reductions in human activity, such as road closures during salmon spawning, could mitigate adverse effects and allow bears to increase salmon consumption.

Co-authors and research collaborators at the Kitasoo Xai’xais Stewardship Authority are already implementing measures to manage human activity to reduce impacts to bears in forestry planning and policies.

“This is the first work that tackles the relationship between land disturbance and the bear-salmon relationship in Kitasoo Xai’xais territory and the Great Bear Rainforest at large. Given the immense cultural and economic importance of bears to the Kitasoo Xai’xais Nation, this work helps inform our more precautionary approach in land-use planning.”

Dr. Christina Service

Citation

Adams MS, Levi T,  Bourbonnais M,  Service CN, Artelle K, Bryan H, Paquet P, Nelson T, Darimont CT. 2024. Human disturbance in riparian areas disrupts predator–prey interactions between grizzly bears and salmon. Ecology and Evolution,  14, e11058. https://doi.org/10.1002/ece3.11058

Abstract

Wildlife must increasingly balance trade-offs between the need to access important foods and the mortality risks associated with human-dominated landscapes. Human disturbance can profoundly influence wildlife behavior, but managers know little about the relationship between disturbance–behavior dynamics and associated consequences for foraging. We address this gap by empirically investigating the consequences of human activity on a keystone predator–prey interaction in a region with limited but varied industrial disturbance. Using stable isotope data from 226 hair samples of grizzly bears (Ursus arctos horribilis) collected from 1995 to 2014 across 22 salmon-bearing watersheds (88,000 km²) in British Columbia, Canada, we examined how human activity influenced their consumption of spawning salmon (Oncorhynchus spp.), a fitness-related food. Accounting for the abundance of salmon and other foods, salmon consumption strongly decreased (up to 59% for females) with increasing human disturbance (as measured by the human footprint index) in riparian zones of salmon-bearing rivers. Declines in salmon consumption occurred with disturbance even in watersheds with low footprints. In a region currently among the least influenced by industrial activity, intensification of disturbance in river valleys is predicted to increasingly decouple bears from salmon, possibly driving associated reductions in population productivity and provisioning of salmon nutrients to terrestrial ecosystems. Accordingly, we draw on our results to make landscape-scale and access-related management recommendations beyond current streamside protection buffers. This work illustrates the interaction between habitat modification and food security for wildlife, highlighting the potential for unacknowledged interactions and cumulative effects in increasingly modified landscapes.

Select figure

Authors and Affiliations

Megan S. Adams^1,2,3,4 
Taal Levi⁵ 
Mathieu Bourbonnais⁶ 
Christina N. Service^1,7,8
Kyle Artelle^1,2,6,9
Heather Bryan_^1,2,3,10
Paul Paquet^1,2 
Trisalyn Nelson¹¹ 
Chris T. Darimont^1,2,3

1. Department of Geography, University of Victoria, Victoria, British Columbia, Canada
2. Raincoast Conservation Foundation, Sidney, British Columbia, Canada
3. Hakai Institute, Campbell River, British Columbia, Canada
4. Central Coast Indigenous Resource Alliance, Campbell River, British Columbia, Canada
5. Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon, USA
6. Department of Earth, Environmental and Geographic Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
7. Kitasoo Xai’xais Stewardship Authority, Kitasoo Xai’xais First Nation, Klemtu, British Columbia, Canada
8. School of Environmental Studies, University of Victoria, Victoria, British Columbia, Canada
9. Department of Environmental Biology, and Center for Native Peoples and the Environment, State University of New York, College of Environmental Science and Forestry, Syracuse, New York, USA
10. Department of Ecosystem Science and Management, University of Northern British Columbia, Prince George, British Columbia, Canada 
11. Department of Geography, University of California Santa Barbara, Santa Barbara, California, USA

You can help

Raincoast’s in-house scientists, collaborating graduate students, postdoctoral fellows, and professors make us unique among conservation groups. We work with First Nations, academic institutions, government, and other NGOs to build support and inform decisions that protect aquatic and terrestrial ecosystems, and the wildlife that depend on them. We conduct ethically applied, process-oriented, and hypothesis-driven research that has immediate and relevant utility for conservation deliberations and the collective body of scientific knowledge.

We investigate to understand coastal species and processes. We inform by bringing science to decision-makers and communities. We inspire action to protect wildlife and wildlife habitats.