Rainforest Solutions Project

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


Do Bears Fish in the Woods?

November 22, 2001

Scientific detective work has discovered why a delicate Canadian ecosystem is changing. unravels a complex tale of bear necessities.

Wearing night-vision goggles, Tom Reimchen manoeuvres the inflatable Zodiak boat around the rocks, deadfalls, and barnacles as we proceed in the dark up an estuary on Canada’s Pacific Northwest. We leave brilliant bursts of bioluminescence in our wake, as schools of fleeing salmon agitate the unicellular algae called dinoflagellates. Why the ‘dinos’ produce light is open to interpretation. One recent hypothesis, Reimchen tells me, is that the light attracts fish which in turn eat the zooplankton that are predators of the dinoflagellates.

Reimchen is a new breed of holistic evolutionary geneticist, whose work focuses on relationships between species rather than on what drove them apart. A professor of biology at the University of Victoria, British Columbia, he specialises in predator-prey interactions. We are here to observe black bears catching spawning salmon (the bears get most of their catch in the dark). This is part of an investigation born eight years ago at Bag Harbour in the Queen Charlotte Islands. As Reimchen sat under giant trees, looking at half-eaten salmon carcasses strewn throughout the forest, he realised that the abundance of carcasses and the abundance of the giant trees adjacent to the salmon river was probably not a coincidence. He has since collected evidence that the autumn return of salmon from the open Pacific Ocean to their natal streams constitutes a major entry of marine nutrients into estuaries and coastal watersheds. He compares it to the great migrations of the wildebeest on the Serengeti plains: both are temporarily very abundant, spatially constrained, relatively easy to capture, and more or less predictable.

Reimchen estimates that 70 per cent of a bear’s annual protein comes from salmon, and that during the 45 days of the spawn each black bear catches about 700 fish and leaves half of each carcass in the forest. At 2.2kg per fish, this amounts to 120kg of nitrogen fertiliser per hectare of land. British Columbia’s 80,000 to 120,000 bears could be transferring 60 million kg of salmon tissue into the rainforest, accounting for half of the nitrogen fixed by some old-growth trees.

The Zodiak carries us out of the salty estuary and up the Klekane River into the conifer rainforest. After the boat has been safely tied up at the bank, Reimchen leads me and the other passengers – graduate student Deanna Mathewson, assistant Dan Klinka, and veteran filmmaker and naturalist Bristol Foster – following a creek, into the pitch-black woods. To avoid surprising any bears, Reimchen trudges steadily along uttering low guttural sounds. Then, at the edge of the creek we stop and wait quietly, listening to the riffles of water against rock, and salmon splashing. With my night-vision goggles, I scan the forest on the opposite bank; an infrared beam taped to the goggles accentuates the grainy image.

‘There is a bear downstream walking towards us,’ someone whispers softly. I see a shadowy movement. The bear is perhaps 75 metres away. The splash of the footsteps sounds closer than the animal appears through the goggles. The bear lunges forward, crashing through the water, but is unsuccessful at catching a fish. Moving upstream slowly, to within perhaps 15 metres of us, the bear takes another lunge. Again, no catch. On its fourth try, it succeeds. I hear the crunch of fish skull, and the bear disappears into the forest with a big chum salmon in its mouth.

Black bears favour the bigger chum salmon over smaller pink salmon; they eat pink in the stream, and usually carry chum salmon into the forest. At Bag Harbour, Reimchen predicted that bears would take larger and more valuable salmon further into the forest, where other bears and scavengers would be less likely to interfere. This led Reimchen deeper into the forest in search of carcasses. Occasionally, he found them 200m from streams. His prediction was correct and he speculates that parts of carcasses would be found even further into the forest, if he looked. ‘We need a new definition of riparian habitat,’ he says, referring to the forest zone influenced by the stream. ‘It is much wider than ever imagined.’

The bear returns in about 15 minutes and starts fishing again, by swatting and grabbing. Bears have various techniques. Some grizzly bears, observed catching pink salmon at Knight Inlet, stand still in deeper water and turn their submerged head from side to side. Some patiently wait and then just flop in on their bellies. Reimchen says that at Bag Harbour, during the day, black bears would just wade in and snorkel, or search overhangs and logs, and catch fish without any great motion. ‘Salmon are more quiescent at night and can easily be approached in the water,’ he says. ‘At night I can pick up a big chum salmon; as long as I don’t take them out of the water, or squeeze them too hard, they allow me to hold them’.

Some bears eat only parts of the fish—- they bite out the brain, or strip out just the eggs. Often I see nothing left of the fish except for a set of intact testicles draped over a rock or mossy log. Reimchen is not sure why. ‘The bear is showing the male salmon respect,’ he jokes, then goes on to explain that testes are composed mainly of nucleic acids (DNA) and that these are metabolically difficult to deal with because they may yield high levels of nitrogenous toxins when digested. In contrast, eggs are primarily yolk (oils). Often bears delicately skin and eat only the fattest parts of the fish, and leave the rest on the forest floor for numerous scavengers including eagles, martens, ravens, crows, gulls, beetles, and fly larvae. After the fly eggs hatch, nothing else will touch the carcass.

Reimchen has observed bears, night and day, for hundreds of hours, and inspected and weighed thousands of fish carcasses. We find scores of fish remains strewn on the forest floor, and something that surprises Reimchen – eight chum salmon, left in a group, only feet apart, with only their heads eaten. I’m leaning over a carcass photographing it when Reimchen arrives, and asks: ‘Did you move these here to photograph them?’ Reimchen has never seen this kind of ‘caching’ before. ‘This might even be the work of wolves’, he says of the discovery. Wolves have been filmed catching salmon, and even deer and squirrels have been observed feeding on dead carcasses. I watch him and Deanna Mathewson work. They examine, weigh and measure each fish – lower jaw length, body length, sex, weight of testes or number of eggs in body cavity and number of eggs on the ground, position of carcass and distance from stream, body condition, intactness of carcass, and presence or absence of brain.

‘Black bears catch more males than female fish’ Reimchen explains. ‘Males are always darting around, fending off other males, and chasing females, while females are more likely to conceal themselves in the shadows, under a log. Male fish are also in the stream longer than females, and the distinguishing hump on their back may be an advantage to the bear.’ In addition to watching bears at night, Reimchen and his colleagues collect tree cores and plant tissue samples during the day, in as many watersheds or ‘systems’ as possible. During his initial research in Bag Harbour, Reimchen reckoned that he could look at historical trends in salmon abundance by examining the yearly growth rings of trees. Salmon numbers entering Bag Harbour have ranged from 500 to 35,000 over the last 50 years. Presumably tree rings would be thicker in the years salmon were more abundant. But Reimchen didn’t know how he could rule out some independent external factor – for example, both tree growth and salmon abundance might determined by rainfall. Then a colleague of Reimchen’s, Joseph Rasmussen at McGill University in Montreal, suggested that Reimchen look at nitrogen isotopes, specifically the proportion of nitrogen 15 (N15), a traceable marker that exists at higher levels in salmon than in the air. N15 is found in the ocean at progressively higher levels of concentration with each successive trophic level. Salmon, as a fourth level consumer, has a distinctly high N15 signature, which would show relative contribution of the marine-derived nitrogen to plants and trees.

At the time, a mass spectrometer capable of measuring minute quantities of N15 in wood didn’t exist. It took four years of tests and false starts before Reimchen found a laboratory in Davis, California, that could modify the combustion chamber in their equipment to allow trace amounts of N15 in wood to be measured. Reimchen got the technology he needed. Now, day after day, Reimchen and Dan Klinka use specialised drills to extract 15mm cylindrical cores from old-growth cedar, spruce, and hemlock trees. Each tree, and the distance it is from the stream is measured, and coordinates are established at each site with a global positioning system. Each core is placed in an individual plastic tube and labeled.

First Nations elders as well as early European settlers speak of rivers which once had thousands of salmon but these disappeared or became rare in the last 100 years. Such stories are commonplace and are largely rejected by fishery biologists as exaggeration. In other cases, some rivers and streams today have no salmon and no one is around who remembers whether salmon existed there in the past. ‘Now, for the first time, we have a method of evaluating relatively easily the presence or absence of salmon in such rivers and perhaps their relative abundance’, Reimchen says.

Meanwhile Mathewson collects live tissue from ten species of plants – black huckleberry, red huckleberry, salal, false azalea, false lily of the valley, hemlock needles, devil’s club, and false buykave. ‘I find more huckleberries in salmon streams than non-salmon streams’, she says. Reimchen concurs that in streams where there are no salmon (Beiu creek, for example, where a waterfall and steep banks guarantee that no fish could been taken into the forest), the cedar trees are small; salal, false azalea, and deer fern are sparse; and the soil is exceptionally poor. ‘I want to understand what proportion of these differences are due to the presence or absence of salmon, and perhaps the relative numbers of salmon that swam up each stream, hundreds of years ago.’

This research is influencing other scientists such as Jonathan Moran, also at the University of Victoria, who studies soil nitrogen, and could lead to satellite imaging of trees enriched with salmon nutrients, and maps showing vital arteries that link the natural world. Analysis of hair from grizzly bears that became extinct in Oregon’s Columbia River Valley in 1931 have shown that 90 per cent of their diet came from salmon. Even grizzly bears 1,100-1,300km from the ocean had consumed salmon. The work may even provide new insights into the historical movement of salmon-dependent First Nation people.

The findings also feed into debates over conservation issues, with respect both to salmon and the forest. The goal of some policies has been to conserve the fisheries for human exploitation, regarding birds and animals as costly competitors. In the past, Alaska had a bounty on eagles because they ate salmon. In British Columbia, until the early 1970s, it was routine for ‘Creek Guardians’, hired by the Canadian Department of Fisheries and Oceans, to walk the streams, count fish, and shoot bears as part of their job. Last year some 4,400 hunters were permitted to kill 400 grizzly bears and 4,000 black bears in British Columbia. The actual number killed by poachers and others is as unknown as the ecological implications of the hunt.

‘Bears have a minor affect on running salmon, contrary to what conservation officials believe,’ says Reimchen. ‘Few predators take more than 10 per cent of their prey population; people take between 40 and 75 per cent of the salmon run.’ At Bag Harbour Reimchen found that about 70 per cent of females were spawned-out at the time of capture, and the average male had spawned about six times prior to capture.

‘People act as if they harvest the surplus, and are the only harvesters. They think that all the dead fish in the stream are wasted,’ says Reimchen. ‘But in ecosystems there is no surplus. Everything is used.’ Not only do salmon replenish the forest but they also vitalise streams and estuaries with carbon, nitrogen, phosphorous, and micro-nutrients. Nearly 50 per cent of the nutrients that juvenile salmon consume comes from dead parents.

Reimchen points to commercial fisheries and habitat loss through poor forestry practices for substantially reducing the number of salmon over the last 100 years. British Columbia has 25 per cent of all the coastal temperate rainforest in the world, and 39 per cent of it has already been logged. And while the government has committed 12 per cent of forest to protected status, there is a major flaw in the plan. According to organisations such as the Sierra Club, the David Suzuki Foundation, and others, the critically low elevation forests – the valleys, where the best timber is, and where the salmon and bears are – are absent from this 12 per cent.

‘All the systems are either logged, un-logged, or slated to be logged, and they may or may not have fish in them,’ Reimchen says, pointing to the big rocks in the mouth of Salmon River where, according to the Canadian Department of Fisheries and Oceans, there were once 40,000 fish spawning. ‘Look at this mess, all this big broken rock left behind, sits here, in the mouth, and all the gravel that is good for spawning is now out in the bay, because of the clear-cut logging here forty years ago.

That is why there are no salmon here anymore.