Diversity of salmon species a necessary metric to understanding how bears feed

Recent study shows importance of salmon species diversity in coastal black bear diets. Species diversity of salmon in watersheds best predicts how much salmon black bears consume.

A black bear on the left is standing on large mossy rocks. There is a stream with a small water fall the right, and a salmon is jumping out of the water in the direction of the bear. The bear has its left paw extended. It looks like a sunny day, although the sky is not in the photo.

Photo by Cael Cook.

Christina Service, a Spirit Bear Research Foundation and Raincoast scientist and PhD candidate at the University of Victoria, led a team that used chemical techniques (stable isotope analysis) on hair samples from black bears to estimate their salmon consumption, a measure that strongly relates to population productivity and health.


Managing salmon for wildlife typically focuses on providing enough biomass.

Salmon biomass is a measure of the total kilograms of spawning salmon. Many who are in the role of implementing conservation strategies and policies think that when it comes to bears, or terrestrial wildlife, more salmon biomass simply means more eating.

However, our recent research published as an open access paper at Journal of Animal Ecology, demonstrates that this assumption, which is core to many of conservation strategies, may not hold. Rather, salmon species diversity may trump salmon biomass when it comes to important considerations for hungry bears. But first a little context.

Background

This research really started in 2009 and was modelled after the Heiltsuk Nation’s early bear monitoring efforts that date back to 2006. The Salmon Carnivore Project, of which this research is a part of, has always tried to understand salmon and bear interactions. This project is a massive undertaking; a Raincoast collaboration with the Heiltsuk, Wuikinuxv, Gitga’at, Nuxalk, and Kitasoo/Xai’xais First Nations across 22,000km2 of their territories, in what is now often referred to as the Great Bear Rainforest.

In concordance with the Indigenous laws of collaborating Nations, the project is designed to be non-invasive so as to minimize harm and interference with the bears we monitor. As such, our monitoring approach is relatively basic and low-tech, we simply build barbed wire corals with a tantalizing scent to entice bears to enter our sampling site and leave us with the immensely valuable gift of hair. This gift is a gold mine for scientists; from just 1 mg of material we can learn about the bear’s species, sex, individual identity, hormone profile, and salmon consumption over the past year.

I’ve been involved since 2010 where I worked on the Heiltsuk node of the project based out of Bella Bella. It is here that I first began to learn about the ecology and geography of this landscape, and how to wield a fencing tool to build the optimal sampling site. In 2012, I moved north to the community of Klemtu, where I began collaborating with Kitasoo/Xai’xais territory on a bear monitoring program. Since that time, three other project “nodes” driven by the investments and foresight of the Wuikinuxv, Nuxalk, and Gitga’at Nations have joined this collaborative effort.

The spatial scale of this collaboration is important because bears regularly cross territorial boundaries. Additionally, bears occur at relatively low density, so to be able to get enough samples, enough data, to see the patterns and trends and interrelationships, it takes a significant research plan across a large landscape. The power of collaborating across this spatial scale was demonstrated in our recent research where multiple collaborating Nations were able to assemble a massive dataset; we analyzed non-invasively sampled hair from 379 black bears and 122 grizzly bears. From such a large dataset we were able to start to disentangle the complex relationship between bears and salmon.

“You can’t understand our bears without understanding salmon”. Those were some of the first words Heredity Leadership of the Kitasoo/Xai’xais counselled me as we embarked on crafting the bear project in Klemtu. Our recent research has been guided by this ethos. Specifically, what characteristics of salmon contribute to bear consumption?

The first step of tackling this question is recognizing that, despite the convenience of using the catch-all term “salmon”, the five main species of Pacific salmon present in this landscape offer dramatically different eating opportunities. One salmon species is not the same as the next. In fact, they differ from each other in many ways; they spawn at different times and in different habitats, have different body masses, and offer differ nutritional profiles of fat and protein content. Human fishers know this intimately, and of course, as our research reiterates, so do bears.

We reasoned that if you’re only looking at salmon biomass, and not diversity, then you’re not really going to understand the full picture of how to best provide salmon for bears. With a diverse “portfolio” of salmon species, bears have more days throughout the year where fish are in the rivers and available for foraging, and more stream sections they can fish in. By contrast, biomass summed across species (for which we currently manage for), is less useful for bears if it comes in all the same time (e.g., via only one species). Despite bears best efforts they can only fit so much in their bellies at one time. Just like us, bears get full. This is important as the more salmon bears eat, the better their populations fare, with benefits including better body conditions at the scale of the individual to greater densities at the scale of populations.

A black bear facing towards the camera and shaking water out of its coat. The water is catching the light to it looks like the bear is surrounded by a blue and purple and yellow and teal glittery rainbow.

Photo by Cael Cook.

Our research

We asked whether consumption patterns were affected by biomass, salmon diversity, and competition with other bears, both black and grizzly.

Our study found that salmon biomass did not affect salmon consumption, at least in the relatively productive watersheds in this region. Rather, salmon species diversity had a large and positive effect. For example, the same amount of salmon biomass across four species allowed black bears to consume ~3 X more salmon each year compared to a scenario in which the same biomass comprises one large run of a single species (see infographic).

This pattern is likely driven by the fact that each salmon species offers bears very different fishing opportunities by using different parts of the river to spawn and arriving at different times throughout the year.

For example, although the simulated removal of two species in a watershed in our study area that naturally hosts four species may only result in a biomass drop of ~3%, the total spawning channel length that is fishable by bears drops by ~60%. Additionally, the total number of days that salmon are in the river and vulnerable to predation decreased by 30%.

Grizzly bears also played a role in salmon consumption by black bears. Black bears consumed ~40% less salmon when they co-occurred in watersheds with grizzly bears.

Open access article

What this means

For Douglas Neasloss, Chief Councillor and Resource Stewardship Director for the Kitasoo/Xai’xais Nation, these results hit home. His home community of Klemtu has invested in development of a conservation-based economy that relies on bear viewing.

Neasloss is concerned that the federal government’s current salmon management focuses on large salmon runs and often ignores smaller runs that often contribute disproportionately to diversity.

Broadly, these results provide insights to managers of both terrestrial wildlife and fisheries. Should managers want to maintain opportunities for bears to eat high levels of salmon, maintaining the diversity of species present in watersheds will be key. This requires safeguarding smaller, less commercially important salmon species, often neglected in salmon management.

Looking up at two women maneuvering wire on either side of a tall, thin tree in a forest. The one on the right is kneeling down, and the one on the left is standing with a coil of silver wire in her right hand. There is sunlight filtering through the trees high overhead.

Krista Duncan, Kitasoo/Xai’xais and Christina Service assembling a non-invasive hair snagging corral.

Christina Service, with the Applied Conservation Science Lab at UVic.

Christina Service

Christina Service, a Spirit Bear Research Foundation and Raincoast scientist and PhD candidate at the University of Victoria, led a team that used chemical techniques (stable isotope analysis) on hair samples from black bears to estimate their salmon consumption, a measure that strongly relates to population productivity and health. @CN_Service

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