How do salmon declines affect coastal bears? And how much salmon biomass is required to sustain terrestrial species?
These are questions many people are asking in light of the increasing number of salmon runs that fail to return as expected to fall spawning streams.Raincoast scientists directly address this question with the Salmon Carnivore Program. Referenced against a backdrop of historical and contemporary declines in coastal salmon runs, we suspect that bears and wolves now receive a fraction of the salmon they once did.
Using hair collected from (non-invasive) fur snagging stations, we use DNA and isotopes to track bear numbers, estimate how much salmon coastal grizzlies are consuming and elucidate the relationship between salmon and bear numbers. We use hormonal assays to give us information about potential stress, reproductive activity and protein deprivation bears might show in response to poor salmon returns.
Current thinking in conservation science instructs salmon management to include the bears, wolves and other wildlife that have an evolutionary reliance on the annual pulse of nutrients and energy delivered via spawning salmon. Even the Department of Fisheries and Oceans Canada’s Wild Salmon Policy recognizes the need for management to transcend salmon ‘production’ alone and consider the needs of terrestrial species.
For this policy to be meaningful however, it requires fisheries managers to consider bears and wildlife by lowering catches and allowing more salmon to reach the rivers to spawn. Currently, humans engage in what ecologists call ‘exploitative competition’ – we capture salmon en route to spawning grounds before they can reach awaiting carnivores. Even salmon runs that spawn in protected watersheds and parks are subjected to exploitation by commercial fisheries at levels as high as 80 percent. Often, these parks were created to protect species such as grizzlies, black bears and wolves. As such, we suspect that grizzly bears in particular, receive a fraction of the salmon they are used to, which ultimately manifests in population declines. Not by ‘die-offs’ as some have speculated, but through repeated years of low birth rates.
In some areas, we also believe it is time to establish truly protected salmon runs – runs that would be managed solely for their importance to wildlife and ecosystems. This would allow salmon to return to spawning grounds without encountering the nets of the Pacific salmon fleet. And those fish would then spawn in rivers that flow naturally without their watersheds logged, developed or otherwise impaired.
Of course, it is not just fishing nets that rob bears and other wildlife of their energy needs. Fish farms, climate change, habitat loss, fresh water withdrawals, changing ocean conditions and processes, and more all influence salmon abundance. Many of these impacts are hard to predict, are indirectly related to salmon abundance, or require complex solutions. In contrast, reducing or eliminating exploitation – on at least some runs – is straightforward and would have an immediate and direct positive effect on coastal wildlife.