On Earth Day our thoughts at Raincoast Conservation Foundation turned to two of the most iconic species in British Columbia, wild salmon and grizzly bears, as well as their intertwined relationship and how the choices we make are inextricably linked to their fates.
Despite the knowledge that many species depend on salmon, humans have never managed fisheries with wildlife in mind. A salmon can enter a fishing net or the mouth of a grizzly bear, but can we manage for the interests of both?
In a new article, "Using Grizzly Bears to Assess Harvest-Ecosystem Tradeoffs in Salmon Fisheries", published last week in the scientific journal PLoS Biology, researchers from the Raincoast Conservation Foundation and the University of California Santa Cruz suggest that allowing more salmon to spawn in coastal streams can often benefit grizzly bears, other ecosystem recipients and salmon fisheries in the long term -- a scenario that serves ecosystems and humans.
In reaching this conclusion, the team first focused on the relationship between grizzly bears and salmon. When salmon are plentiful in coastal streams, bears thrive and produce more (up to four) cubs. Grizzlies also occur at higher densities and grow to larger sizes when there is abundant salmon. Importantly, when salmon are plentiful, bears eat less of each fish, selecting the nutrient-rich brains and eggs and casting aside the remainder. These salmon remains then feed other animals, scavengers and fertilize the adjacent streamside zone. Thus, abundant salmon boosts the amount and value of food for bears, as well as transfers more nutrients and energy to other consumers.
In contrast, when salmon are scarce, grizzlies produce fewer cubs, if any, and eat more of each individual fish. Less discarded salmon enters the surrounding ecosystem with fewer benefits for other wildlife and ecosystem components.
What was a surprising finding, however, was that letting more fish spawn would also benefit future fisheries. The article's authors argue that, in four out of six study areas, allowing more salmon to spawn would mean more salmon in the ocean. This translates to larger harvests over the long run, which would require managing salmon fisheries differently, i.e. lowering harvest rates in the short term. Commercial salmon fisheries typically extract 50 per cent or more of the salmon bound for rivers, bears and the forests.
Given this obvious benefit, why are salmon not already managed this way? When the number of salmon returning to spawn from their ocean migration is variable, fishery managers favour the short-term benefit of harvesting every year, even when salmon abundance is low and even if it results in giving up larger harvests in the future. The authors argue that if society values both
bears and the fishing industry, then managers should reconsider current practices and adopt this new strategy.
In the cases where competition between grizzlies and humans does exist, the researchers calculated how much helping bears could cost the fishing industry in lost catches. They predicted the cost would be approximately $500,000 to $800,000 annually. These contested areas are on the Fraser River, where remaining grizzlies are highly threatened and increases in
salmon spawners could help recover threatened or lost grizzly bear populations. Even though the study did not examine this, Raincoast has elsewhere identified the growing tourism value of spawning salmon and bear viewing, a consideration that could be weighed against losses to the
Another important aspect of the study is that the sockeye fisheries examined are certified as sustainable by the Marine Stewardship Council (MSC). The research suggests the MSC principle that fisheries "have minimal ecosystem impact" might not be satisfied in the Fraser River, given that this fishery is likely impacting grizzly populations.
As society becomes increasingly aware, albeit slowly, of the principles of sustainability, this study reinforces the message that taking steps to protect the greater ecosystem, in this case bears and other wildlife, ultimately serves our own interests in the long run. And the sooner we implement such an approach, the less painful it will be in the future -- something that would serve us well to reflect upon.
This article was co-authored by Misty MacDuffee, a conservation biologist with Raincoast Conservation Foundation, and Raincoast's science director Dr. Chris Darimont.