The Sacred Link – Bears, Salmon and Ancient Forests
Story by Margaret Munro with Photography by Nick Didlick
Cruising through a sea of plankton far out in the North Pacific the sockeye was feasting on a rich source of protein that allowed it to grow rapidly, and make its remarkable migration back to its spawning stream on the West Coast of North America. As it splashed upstream in a small, clear river on the Queen Charlotte Islands, a long legged black bear leaped off the bank and with a single swipe, threw the salmon up onto the shore. There, with a quick bite to the head, it killed the salmon, feasting on the richest parts before going fishing again.
Birds picked over the carcass, then bugs took their turn. It was only then that biologist Tom Reimchen came along and added the decomposing fish to a remarkable study that has found that salmon – and the bears that yard them out of streams by the tonne – transfer a massive amount of essential nutrients out of the sea and into the forest.
He and his colleagues at the University of Victoria, who have examined thousands of such fish for their on-going work, are tracking marine nitrogen as it winds its way through the forest ecosystem and ends up in insects, tree tops and bird feathers.
They figure that up to half the nitrogen in some trees comes from the sea through nature’s remarkable system of transference.
They also estimate that up to 80% of the salmon that enter streams on the Pacific coast can end up on the forest floor. In one stream the researchers studied in the southern Queen Charlottes, eight black bears each hauled about 1,600 kilograms of salmon into the forest.
That’s about 720 salmon each, says Prof. Reimchen, who inspected the remains and found that the bears ate about half of the fish, leaving about 6,400 kilograms for other scavengers.
The bears like the brain and the muscle but they don’t like the guts, so typically that part of the fish is untouched, says Prof. Reimchen, adding that most of the fish spawned before the bears caught them.
He estimates B.C.’s bears could be carrying 60 million kilograms of salmon into the woods every year.
All of which begs plenty of questions about the importance of both bears and fish to the forest ecosystems.
“In the old days there were bears and salmon on almost every stream, Prof. Reimchen points out. Today, urban growth and hunting pressure has reduced the number of bears. At the same time salmon runs have declined so dramatically in some watersheds that bears have been found starving, as they were last fall in British Columbia’s Rivers Inlet.
Salmon runs in Washington and Oregon are estimated to be 10% of the size they were a century ago, while runs on B.C coast are down over 50%.
I’d be hesitant to say forests need the salmon, says Prof. Reimchen, noting that trees grow just fine far from salmon streams. But salmon definitely contribute to healthy forest ecosystems.
Federal fisheries officers as recently as the early 1970s shot bears they saw on salmon streams, thinking they were killing spawning salmon. While that is no longer allowed, Prof. Reimchen says fisheries managers still take a pretty blinkered view of the world.
They treat salmon and humans as a two-species ecosystem, where people are the single user and can take the biological surplus, says Prof. Reimchen.
In fact, there is no biological surplus, he says. The surplus, in fact, is what’s used by all the other species utilizing the salmon, be it bears, seals, or seal lions or the forest.
Recent studies have highlighted the importance of specific salmon runs to killer whale populations, and in the Shushwap region, biologists have long known of the tight link between salmon runs and resident trout populations. The year following a big spawning run in the Adams River, there is a boom in trout populations, as they feed on the insects and plankton stimulated by the rotting carcasses.
Scavengers abound in watershed with healthy salmon runs. There are more eagles, crows, ravens, martens and insects. The insects not only feed salmon fry, but they also attract species like flycatchers and wrens, the feathers of which the researchers are collecting and analyzing for evidence of compounds from the sea.
They do this by measuring the level of nitrogen-15, an isotope that is much more prevalent in the sea than in air or on land. Trees that do not grow near the sea, or along salmon streams, contain almost no N15. The Victoria researchers have found that nitrogen in trees growing within 100 metres of a salmon stream can be up to half N15.
We can, at least in theory, go to any watershed on the coast and get some insight into the history of the watershed in terms of salmon,” said Prof. Reimchen. Right now I can state unambiguously that when salmon are present the trees have an extremely rich signature of nitrogen isotopes that come from the salmon.
Biologists have long assumed nutrients flowed from the forests into the streams and into the oceans and that was it, he says. This indicates the flow is bi-directional. The salmon are bringing back nutrients derived from the middle of the ocean – and the bears are yarding them into the forest.