Rainforest Solutions Project

Promoting conservation and economic alternatives in British Columbia's Great Bear Rainforest


Fish and the Forest: New research shows salmon are feeding B.C.‘s coastal ecosystems

August 8, 2002

Under a clear, starlit sky, Tom Reimchen pushes away from the anchored Blue Fjord, guiding a small Zo-diac toward the mouth of the Salmon River somewhere up ahead.

It is 11 p.m., and 16 hours into another day of fieldwork, the University of Victoria biologist shows little sign of fatigue. If anything, he’s more alert. Perhaps it’s because there’s so much for him to see in this rich estuary in the islands of Gwaii Haanas, a Haida heritage site and national-park reserve on the south end of the Queen Charlotte Islands.

Thousands of translucent jellyfish float at the surface. A seal glides by, the bright light of the full moon dancing off its mottled coat and upturned ebony eye. Bats flit up and down, twisting in flight, while a lone bald eagle heads up the inlet to alight on a distant cedar snag.

As an invited guest, I am in for a much-anticipated treat. In a half-hour, I will waddle in a thick orange survival jacket and hip waders over slick tidal rocks onto a grassy shoreline. From there, I will tread behind Reimchen and fellow biologist Bristol Foster into the black forest for a midnight rendezvous with some big, hungry bears.

For the past decade, Reimchen has been immersed in a unique study of forested coastal valleys. While he’s worked, an assortment of environmental activists from near and far have waged an unrelated campaign to protect an area on the mid- and north coasts that they call the Great Bear Rainforest.

In important ways, bears occupy an essential niche in this vast wilderness, just as they do on isolated archipelagos such as Haida Gwaii, otherwise known as the Queen Charlotte Islands. Important as they are, though, bears are but one part of a chain whose first and arguably most important link is salmon.

To understand what makes coastal B.C. so special, we would do well to stop thinking of this magical place as the Great Bear Rainforest (100,000 hectares of which the former B.C. government protected in April 2001) and begin appreciating it for what it is, or at least was, until not so long ago. Without doubt, this place more properly deserves to be called the Great Salmon Forest.

And if the objective is to protect that forest for future generations, then the focus must be squarely on conserving salmon. In Reimchen’s eyes, that means doing a host of things differently. It means reducing dramatically the number of fish we catch overall, especially in the commercial fishery. It also means being far more selective in what we catch, because it turns out that some salmon are more important to forests than others. And, finally, it means changing the way we log streamside forests. If we strike out on all three counts, hundreds of thousands, if not millions, of hectares of forest may never be the same again.

In the early 1990s, Reimchen’s thoughts on the salmon forest began to take form. At Bag Harbour Creek on Moresby Island, to the south of the Salmon River, Reimchen first chronicled the feeding habits of the archipelago’s genetically distinct black bears.

What he discovered was that during one not particularly strong salmon spawning cycle in just one river system on this island chain 100 kilometres west of Prince Rupert, resident bears carried 6,200 kilograms of salmon out of the water and into the woods.

The hungry bears devoured about two thirds of that mass of protein. But after eating their fill, they left behind more than 2,200 kilograms of fish guts, scales, and bone, scattered throughout the forest up to 150 metres from the stream. That material, Reimchen later estimated, fed a host of other creatures, from crows and seagulls and bald eagles to ravens and pine martens. As well, portions of uneaten salmon left in the stream fed snails, crabs, starfish, and other marine creatures.

Obviously, the bears played a critical role in spreading an important food source. But because this food varied in volume depending on the number of spawning salmon, bears were not always so generous in what they left behind.

“During the years when smaller numbers of salmon were coming in, the bears took a greater proportion of the total salmon run into the forest. But they ate a greater proportion of each carcass,” Reimchen says. “The consequence of that was there was less biomass, less nutrients available, for the martens and the crows, for the ravens, for the gulls. Very importantly, there was virtually nothing available for the insects.”

But things were dramatically different when salmon runs were high. With more fish to catch, the bears were far more selective in what they ate, concentrating on the most protein-rich parts of the fish and leaving the rest.

“They ate only a small proportion, about 50 percent of each carcass; they high-graded,” Reimchen says. “This resulted in much greater nutrients being available to the martens, the crows, the ravens. And a very large proportion of that went directly to insects, which then drove the bird community the following year.”

In attempting to explain how distinct populations of animals and plants stay in some form of equilibrium in the wild, biologists tend to lean toward one of two camps: the “top down” camp stresses the importance of top predators in controlling species just below them on the food chain; the “bottom up” camp stresses the importance of food supply.

Reimchen’s early work neatly highlighted how these two views are not necessarily either/or propositions. Salmon are a vital source of food to bears and a host of other forest creatures. But the bears play a critical role in determining how that food source is distributed.

When salmon become less abundant, there are significant implications for bears and, by extension, the myriad other creatures that bears deliver the salmon to.

In the absence of enough salmon, Reimchen says, bears don’t put on enough fat. “The females that are pregnant will either reabsorb embryos or the cubs die because the females aren’t producing enough milk..The end result is that the population doesn’t increase. And if the salmon numbers remain low, then when that bear dies, she will not be replaced. So the population will then decline.”

Owing to certain evolutionary forces, those declines may ultimately threaten genetically distinct populations of bears, such as those on Haida Gwaii. Reimchen’s travelling mate and fellow scientist Bristol Foster gained notoriety in the mid-1960s when he published a pioneering article in the journal Nature that surveyed how certain mammals isolated on islands tended to either reduce in size or become larger than their mainland ancestors.

Ironically, his generalized pattern-that big mammals on islands usually get smaller in size while small mammals generally get bigger-did not hold true for Haida Gwaii’s black bears, which found themselves isolated on the archipelago after the last ice age. The bears got bigger.

“Their skulls are relatively massive,” Foster says. “Their back molars are up to one-and-three-quarter inches-grizzly-bear size. They have very large teeth.”

The reason for the evolutionary trend toward gigantism in Haida Gwaii’s bears is, Foster believes, primarily due to the abundance of salmon over millennia-that, and the absence of natural competitors for salmon, such as the distant mainland’s grizzly bears.

Significantly, the trend toward bigness may now have ended. The islands’ bears may be getting smaller, in part because of reduced salmon numbers and because other important food sources, such as berries, are far less available than they were before the introduction of deer to the archipelago early in the past century.

Foster and Reimchen’s appreciation of the important role salmon play in our forests is shared by a growing number of biologists and ecologists. In the early summer of 2000, Washington state’s department of fish and wildlife released a study showing how more than 13-dozen species of fish and wildlife-everything from the biggest bear to the tiniest fly-depend in whole or in part on salmon for their survival. The Pacific Northwest coast simply wouldn’t be what it is without salmon.

This point was underscored in graphic terms to residents of the remote northern B.C. coastal community of Oweekeno three years ago. In the fall of 1999, some local salmon runs collapsed. For the first time that villagers could remember, starving grizzly bears wandered through the community in search of food. The result was the shooting of six bears, including a mother and two cubs. Officials captured and relocated three other underweight and undernourished grizzlies.

These and other stories point to the need to get government agencies in charge of fish and wildlife to think more carefully about the connections between species inhabiting water and species inhabiting land and to adjust their policies accordingly. “We need to start giving out the whole story of what made the ecosystem; it’s an abundance of fish on the spawning grounds,” says Jeff Cederholm, salmon research scientist and principal author of the Washington report.

Bag Harbour gave Reimchen insight into the bear’s role as nature’s courier, the deliverer of vital care packages to a host of creatures that call the temperate rain forest home. But it was the care package itself that later tweaked the scientist’s mind. Could it be that the salmon “fed” the coastal forest itself? And if they did, were certain salmon species more important than others?

After entering the coastal forest, we walk along the banks of the Salmon River, stepping cautiously over the roots of centuries-old western red cedar and Sitka spruce trees. Stopping perhaps 150 metres from the river’s mouth, we catch the occasional glimpse of a star through the maze of tree branches overhead. But the moon is too low to cast its luminous face on us. Enveloped in darkness, we hear, more than see, the gurgling, shallow river before us.

Behind us, a path leads into the forest. Reimchen leaves us and follows what is evidently a bear trail into the woods. He comes back moments later. “There’s three freshly eaten salmon carcasses back there.”

It would be impossible to see in this darkness without infrared night-vision scopes, two of which we constantly swap between the three of us as we look up and down the river. Through the eyepieces, this seemingly subterranean world is rendered in shades of black and green. Before long, we pick out the silhouette of a bear, perhaps six metres to our left.

The bear hunches like a cat readying to spring at an unsuspecting songbird. With a sudden lunge, it is in the middle of the narrow river. But no salmon is caught. Another few leaps while in the river fail to produce a kill, and the bear returns to the bank to try again.

Moments later, a large male bear walks out of the forest onto a log that extends off the bank about six metres opposite us. His acute sense of smell alerts him to our presence. Still, he makes no attempt to move. In fact, he seems downright nonchalant (as does Reimchen, who has spent many such evenings on Haida Gwaii and has come to learn that when salmon are about, the archipelago’s bears show no aggression to humans). The bear sits down on the log and yawns, giving us a clear view of his big teeth. Then he leisurely scratches his neck with his hind paw, showing off his long claws, and lies down, as if to watch the evening’s entertainment.

Before long, we see a third bear. It moves toward us downstream, in the middle of the river channel. The tips of its black coat glisten fluorescent green. As it comes closer, the infrared scope picks up its flashing eyes, more luminous than a traffic light. With a sudden surge, it grabs a pink salmon in its powerful jaws, then carries the thrashing fish back to the riverbank and settles behind a giant spruce tree to feed on its prize.

Up and down the B.C. coast-from the Khutzeymateen Valley, a grizzly-bear haven near Prince Rupert, to Princess Royal Island, home of the famed “spirit” bear, to mid-coast valleys where grizzlies, black bears, and wolves feed on salmon-Reimchen and a dedicated crew of student volunteers have been chronicling what really makes the Great Bear Rainforest tick.

Sockeye. Chum. Pink. Coho. Chinook. Take your pick. By returning to spawn in the numerous rivers and streams, salmon help to feed this delicately balanced ecosystem. But not all salmon species are alike. Some are fatter and richer. Some are just plain bigger. Pink salmon, for example, generally weigh one-and-a-half to two kilograms. By comparison, chum salmon generally range from three to eight kilos.

These big differences in weight have far-reaching consequences for life in the forest. When a bear catches a big chum, it will expend more energy to protect its catch from other bears by carrying its prize deep into the forest. Most often, it will not do the same with the smaller pink salmon.

“If you have a large chum run, you find them [carcasses] strewn in the forest hundreds of metres. But the pinks are nearby the streams, because basically they’re only a couple of mouthfuls,” Reimchen says. “Why would you take a couple of mouthfuls back into the forest when you can deal with it right there?”

A big fish hauled into the forest by a bear usually means a big amount of partly devoured nutrients left behind for other forest creatures to eat and for plants to absorb. In fieldwork, Reimchen and a group of student volunteers have turned their efforts to finding “signatures” of salmon in the trees themselves. The work begins with an odd T-shaped instrument known as an incremental bore.

The tool is commonly used by foresters to calculate the growth rates of trees before deciding what patch of forest should be logged next. It allows the user to bore deep into a tree trunk and extract a pencil-thin tube of wood. The wooden tube is circled in rings. Each ring represents one year’s tree growth.

Several years ago, Reimchen latched on to the idea of using tree rings to termine how trees at varying distances from fish-bearing rivers grow in response to the decaying salmon left behind by bears and other scavengers.

If the tree rings were found to contain the nitrogen isotope N15, it would be a sure sign that salmon were helping to feed the trees. Usually, N15 is almost undetectable in plants. But the isotope is found in the flesh of marine species and is relatively abundant in salmon because of their position near the top of the marine food chain. A reasonable proposition would be that if salmon parts were left near a tree, then as the salmon decayed, that tree would pick up N15.

When the results of the tree-core analysis began coming in, an interesting picture emerged. Reimchen learned that as much as 55 percent of this nitrogen isotope present in core samples taken from some streamside trees originated in salmon. Not only was N15 elevated in some trees, but it also rose and fell depending on salmon abundance. In other words, when historical data compiled by the federal Department of Fisheries and Oceans showed that a salmon run in a particular stream was high, the N15 signature in the streamside tree was high as well. When the same stream had a low salmon run, the resulting N15 signature was also low.

Reimchen believes that his analysis of tree cores will ultimately tell the story of how entire communities of plants and animals respond to changes in the abundance of salmon, whose decaying bodies may also yield calcium, phosphorous, and other trace elements of value to flora and fauna. He also believes that he will be able to show that N15 signatures declined as the relative abundance of chum salmon fell due to commercial fishing pressures that generally targeted larger fish species first, followed by smaller species.

To date, he and a crew of student volunteers have collected samples from 970 trees in 110 coastal valleys, as well as gathered vegetation and insect samples. Analysis of the bugs by Morgan Hocking, a PhD student working with Reimchen, shows that N15 is found in all manner of forest insects. And if it’s found in the insects, then it’s found in the songbirds that feed on the insects, Reimchen says.

More samples are needed before Reimchen will have a clearer picture of where the so-called salmon signature is found. From there, it should be possible to make some fairly reliable estimates of just how large an area of forest may be influenced by salmon. Until then, the biologist is unwilling to volunteer a number.

“What’s called by some the ‘salmon shadow’-I’m inclined to think of it more as a salmon signature-extends right up to the headwaters of the Fraser,” Reimchen says of the 1,370-kilometre-long river. Just how far out it extends from the water’s edge is the big and as-yet-unanswered question. But it’s safe to say it may be a long way. Reimchen cites the finding of another study that found N15 present in samples of bear urine and bear feces up to 800 metres from salmon streams. With thousands of kilometres of Coastal and Interior rivers and streams home to salmon, it’s not unreasonable to think that millions of hectares of forest may be involved.

In the early morning of a new day, I awake from a fitful four-hour sleep. As if the buzz of being within spitting distance of bears in the dead of night wasn’t enough stimulation, I joined Reimchen and Foster for a hot chocolate laced with a generous splash of rum before retiring for the night. An alcohol-sugar high sealed my sleepless nighttime fate. Groggily bumping about in the cramped quarters of the forward cabin, I climb into cold clothes and go in search of coffee.

In the gathering warmth of a new day, we pile back into the Zodiac along with three of Tom’s students. Awash in the rays of a low-lying sun, the forested valley reveals its glory. A whispering breeze through the rain forest’s upper canopy scatters billions of accumulated dewdrops into the air, where they form a fine mist.

The Salmon River is a series of gently curving braids. Between them, giant spruce trees covered in thick mats of moss shoot into the air. Somewhere-a four hour’s walk-ahead lies one of Reimchen’s favourite lakes. Passing underground, the lake water feeds the upper reaches of the river, constantly replenishing it with cool water.

This makes for almost perfect conditions for fish, a fact brought home by the hundreds of pink salmon that wait in a holding pattern in the water, their noses pointed upstream to the distant spawning beds where they will soon travel. For now, they stay in position, their tail fins moving gently back and forth, countering the current.

The number of salmon in this stream would not be anywhere near so robust had clearcut logging occurred here. Reimchen says that his fieldwork shows a marked decline in salmon abundance in logged versus unlogged rain-forest valleys, particularly when logging has proceeded right to a river’s banks.

But the biggest culprit in the disappearance of certain salmon runs and the stark diminishment in others has been from indiscriminate fishing in “mixed stock” fisheries that fail to distinguish between different salmon, Reimchen says.

In the natural world, predators rarely take more than five to 10 percent of the available adult prey. Bears may feed on a whole lot of salmon, but a whole lot more of the fish make it to the spawning beds to help ensure the perpetuation of the species.

Humanity’s drastic overdrawing of the ocean, however, has resulted in a dire situation. In some commercial fisheries, such as the herring-roe fishery, up to 85 percent of the fish are targeted for capture, a significant loss not only for that fish population but for the other fish that feed on herring.

“Nothing less than a fundamental revamp in our estimation of quota-our capture rate-will get us back to what natural systems have dictated over time is acceptable. We as a species have to get down to that five to 10 percent,” Reimchen says. “There isn’t a predator in the world that does what humans do.”

But not all humans are rapacious. In fact there are plenty of examples from the past and a growing number from the present that show how humans can harvest fish without overdepleting stocks.

On my last day with Reimchen, I find myself trailing behind the professor and his student volunteers as we move across a floodplain at low tide. We have left our boat anchored in Mathieson Inlet and are moving toward the mouth of one of two rivers draining into this water body to the south of the Salmon River valley.

We clamber over rocks covered in a toss of orange-and-yellow seaweed and drying sea asparagus. The tops of the surrounding forested hills are obscured in low cloud and mist while up ahead a grove of ancient cedar trees marks the entrance to the river valley.

Archaeological digs near here unearthed a bear tooth dating back to 9200 BC. Bears have been feeding on salmon here for a long, long time. And so have humans. When we arrive at the river’s mouth, we find signs of an ancientweir used by Haida people to steer salmon into a narrowing body of shallow water where they could be captured.

Weirs just like this marked points of settlement all over these islands, which at one point sustained a human population six times greater than it is today. Salmon were caught here and elsewhere in large numbers. But large numbers of fish were also allowed past these structures to spawn and continue the species.

Today a host of selective fishing methods, including weirs, combined with high-profile conservation efforts aimed at staving off the elimination of endangered stocks of coho salmon and steelhead, to name two species, have resulted in some remarkable turnarounds in fish abundance in certain river systems.

In 2001, for example, coho salmon returning to their home streams in the Thompson River watershed spawned at rates 10 times higher than their parents’ generation, thanks in part to stringent conservation efforts and changes to fishing practices.

If that kind of success can be replicated elsewhere over time, bears and a host of other species will be a whole lot happier in the Great Salmon Forest.