Letting salmon escape from nets could benefit grizzly bears and even the fishers, study says

Grizzly eating a salmon
A grizzly bear eats a salmon. A new study says managers must consider the value of salmon to the entire ecosystem. (Jennifer Allan)

A new study suggests that the health of the grizzly bear population is also a strong indicator of the health of Pacific salmon—and perhaps surprisingly, allowing grizzlies to consume more salmon will, in the long term, lead to more, not less, salmon.

The study, led by Taal Levi, of the University of California at Santa Cruz and colleagues from Canada, suggests that allowing some more Pacific salmon to escape the nets of the fishing industry and thus spawn in coastal streams would not not only benefit the natural environment, including grizzly bears, but could also eventually lead to more salmon in the ocean. Thus there would be larger salmon harvests in the long term—a win-win for ecosystems and humans.

The article, “Using Grizzly Bears to Assess Harvest-Ecosystem Tradeoffs in Salmon Fisheries,” was published April 10 in the online, open-access journal PLoS Biology. In the study  Levi and his co-authors investigate how increasing “escapement”—the number of salmon that escape fishing nets to enter streams and spawn—can improve the natural environment.

“Salmon are an essential resource that propagates through not only marine but also creek and terrestrial food webs,” said lead author Levi, an environmental studies Ph.D. candidate at UCSC, specializing in conservation biology and wildlife ecology.

Salmon fisheries in the northwest Pacific are generally well managed, Levi said. Managers determine how much salmon to allocate to spawning and how much to harvest. Fish are counted as they enter the coastal streams. However, there is concern that humans are harvesting too many salmon and leaving too little for the ecosystem. To assess this, the team focused on the relationship between grizzly bears and salmon. Taal and his colleagues first used data to find a relationship between how much salmon were available to eighteen grizzly bear populations, and what percentage of their diet was made up of salmon.

The study looked at Bristol Bay, Alaska, the Chilko and Quesnel regions of the Fraser River watershed and Rivers Inlet on the Inside Passage, just northeast of northern Vancouver Island.
The study says adult wild salmon are “critical” to ocean, river and terrestrial ecosystems. As well as humans, salmon are eaten by orcas, salmon sharks, pinnipeds (seals and sea lions). On land, salmon are eaten by black and grizzly bears, eagles and ravens.

Because the grizzly is the “terminal predator” the study says “if there are enough salmon to sustain healthy bear densities, we reason there should be sufficient salmon numbers to sustain populations of earlier salmon-life history predatory such as seabirds, pinnipeds and sharks.”
As is well known in the northwest, the study says “bears are dominant species mediating the flow of salmon-derived nutrients from the ocean to the terrestrial ecosystem. After capturing salmon in estuaries and streams grizzly bears typically move to land to consume each fish, distributing carcass remains to vertebrate and invertebrate scavengers up to several hundred metres from waterways.”

“We asked, is it enough for the ecosystem? What would happen if you increase escapement—the number of fish being released? We found that in most cases, bears, fishers, and ecosystems would mutually benefit,” Levi said.

The problem, the study says, is that fisheries management have a narrow view of their role, what the study calls “single-species management,” concentrating on salmon and not the wider ecosystem. “Currently,” the study says, under single-species management, fisheries commonly intercept more than 50 per cent of in bound salmon that would otherwise be available to bears and the terrestrial and aquatic ecosystems they support.”

The relationship between salmon and bears is basic, Levi said. “Bears are salmon-consuming machines. Give them more salmon and they will consume more—and importantly, they will occur at higher densities. So, letting more salmon spawn and be available to bears helps not only bears but also the ecosystems they nourish when they distribute the uneaten remains of salmon.”

When salmon are plentiful in coastal streams, bears won’t eat as much of an individual fish, preferring the nutrient-rich brains and eggs and casting aside the remainder to feed other animals and fertilize the land. In contrast, when salmon are scarce, bears eat more of a fish. Less discarded salmon enters the surrounding ecosystem to enrich downstream life, and a richer stream life means a better environment for salmon.

In four out of the six study systems, allowing more salmon to spawn will not only help bears and the terrestrial landscape but would also lead to more salmon in the ocean. More salmon in the ocean means larger harvests, which in turn benefits fishers. However, in two of the systems, helping bears would hurt fisheries. In these cases, the researchers estimated the potential financial cost—they looked at two salmon runs on the Fraser River, B.C., and predicted an economic cost of about $500,000 to $700,000 annually. This cost to the human economy could help support locally threatened grizzly bear populations, they argue.

While these fisheries are certified as sustainable by the Marine Stewardship Council (MSC), the researchers suggest that the MSC principle that fisheries have minimal ecosystem impact might not be satisfied if the fishery is contributing to grizzly bear conservation problems.
The researchers believe the same analysis can be used to evaluate fisheries around the world and help managers make more informed decisions to balance economic and ecological outcomes.


What do grizzlies eat in northwestern BC ?

The current study and previous studies track the grizzly’s diet by studying the nitrogen and carbon istopes in grizzly hair. In one study in the early part of this decade, the BC Ministry of the Environment used guard hairs from “passive hair snags” as well as samples from bears killed by hunters or conservation officers.

The 2005 study says “Guard hairs are grown between late spring and fall, thus integrating the diet over much of the active season of temperate-dwelling bears.” Analysis of the isotopes can show what the bears ate over the season.

The study identified four elements in the grizzly diet across British Columbia, Alaska, Yukon and the Northwest Territories: plants, “marine-derived nutrients” mostly salmon, meat (primarily from ungulates such as moose) and in inland areas, kockanee salmon.

As could be expected, grizzly salmon consumption is highest in coastal areas. Males generally consume more salmon than females, likely because a mother grizzly may avoid taking salmon if there is danger to the cubs from males. The further inland a grizzly is found, salmon is a lesser factor in the bear’s diet. In Arctic regions, grizzlies can feed on arctic char, whales, seals and barren-ground caribou.

So what do local grizzlies eat? (excerpts from the 2005 study, Major components of grizzly bear diet across North America,  National Research Council Research Press  published March 28, 2006)

Map of grizzly diet and salmon
Grizzly consumption of salmon on the northwest coast (NRC)

North Coast 54.54 N 128.90 W (north and west of Kitimat)
Plants 33 per cent Salmon 67 per cent

Mid Coast 52.50 N 127.40 W (between Bella Bella and Ocean Falls)
Plants 58 per cent Salmon 42 per cent

Upper Skeena Nass 56.80 N 128.80 W
Plants 71 per cent Salmon 5 per cent Meat 13 per cent

Bulkley Lakes 54.10 N 127.10 W
Plants 63 per cent Salmon 6 per cent Meat 16 per cent Kokanee 15 per cent

Cranberry 55.40 N 128.40 W (near Kiwancool)

Plants 30 per cent Salmon 17 per cent Meat 40 per cent Kokanee 13 per cent

Khutzeymateen 54.68 N 129.86 W (near Prince Rupert)
Plants 22 per cent salmon 78 per cent



Other authors of the 2010 study are Chris Darimont, UCSC, Misty MacDuffee Raincoast Conservation Foundation, Denny Island, BC; Marc Mangel, Paul Paquet, UCSC and University of Calgary, Christopher Wilmers, USCC
Funding: This work was funded by an NSF GRF and Cota-Robles Fellowship (TL), a NSERC IRDF (CTD), the Wilburforce and McLean Foundations, and Patagonia. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

2005 study by Garth Mowat Aurora Research  Crescent Valley BC and  Douglas Heard BC Ministry of the Environment, Nelson

Scrutiny of Enbridge Northern Gateway plans: II Landslides

Energy Enviroment

598-bigslide.jpgThis photograph from the geomorphology report shows how bedrock spread lead to catastrophic landslides along a 2.5 kilometre scarp (photo lower centre to upper right) and a 1.3 km scarp (photo distance) on the ridge above Parrott Creek. The yellow dashed line delineates the landslides’ headscarp. The arrow shows the direction of movement.

A retired geomorphologist for the BC Forest Service, who lives in Smithers, says a break in the Enbridge Northern Gateway pipeline, triggered by a landslide, is “inevitable” given the highly complex terrain that the pipeline will cross.

James Schwab bases his peer-reviewed paper  on his 30 years experience in northwestern British Columbia.

“The unstable mountainous  terrain across west-central BC is not a safe location for pipelines. Eventually a landslide will sever  a pipeline,” he says.  He calls for investigation of  a safer, alternative route for the pipeline.  

The report was funded by the Bulkley Valley Research Centre.  It examines  three areas, the Nechako Plateau, the Hazelton Mountains and the Kitimat Ranges.

Schwab’s report says the Nechako Plateau appears relatively benign, but, he says, large landslides have occurred in volcanic rock overlying other older volcanic and sedimentary rock.

Along the Morice River,  the report says sediments have historically experienced landslides. Road construction and wildfires have reactivated these landslides. The proposed pipeline corridor crosses an historic earth flow west of Owen Creek, moving sediment along Owen Creek and moving sediments  near Fenton Creek and Lamprey Creek

At  Gosnell Creek, Schwab says, shifting channels on active alluvial fans pose road maintenance challenges at present and, he says, pipelines will likely bring similar challenges crossing these fans. The report says the creek banks are unstable at Crystal Creek and Gosnell Creek pipeline crossing points.

The report says the volcanic bedrock of the Hazelton Mountains is “inherently unstable” and geological  surveys show there were many landslides in prehistoric times. Three more recent documented large landslides within the Bulkley Range of the Hazelton Mountains have severed the natural gas pipeline since its construction in the early 1970s; large landslides have also impacted forest roads and highways.

He says that gravity is deforming the slopes in the  volcanic bedrock found in the Kitnayakwa, Clore and Bernie watersheds and the report calls for a  thorough geotechnical investigation to determine the stability of the bedrock and hill slope in areas before the pipeline is built.  “Avoidance of these unstable hill slopes is generally the preferred engineering development option,” the report says.

The report examines where the pipeline corridor crosses through a mountainside to the southeast of the Clore Canyon.

The highly fractured bedrock in the canyon is undergoing active mass erosion. unstable rock reaches up to about 1200 m above sea level and extends around the mountain into an adjacent tributary valley. This bedrock along the north and west side of the mountain is extensively gullied and contains many landslide scarps and an actively moving landslide.

The active instability of the eastern mountain slope places major constraints on development, Schwab says.

Schwab says the Kitimat Ranges are characterized by steep narrow valleys, which create “colluvial-fluvial fans … at the base of most steep gully channels in the Hoult Creek and Upper Kitimat watershed.” The steep gullies extend from the mountains in to the valley or directly  into Hoult Creek or the Kitimat River.

Many of these high-energy systems  in the Kitimat Ranges experienced debris flows during extreme rainstorms in the fall of 1978 and the fall of 1992. Debris flows commonly occur under seemingly normal storm events during summer convective storms and fall frontal rainstorms.

Debris flows are powerful landslides that can damage or rupture pipelines, the report says.

Hunter Creek, a large active alluvial fan, has historically pushed the Kitimat River across the valley, Schwab’s report says.  In 1992, road and  levée  construction caused a catastrophic channel  change.

The Kitimat trough, on the road between Terrace and Kitimat, is actually a fjord uplifted by ancient geological forces.   The valley has deep deposits of sediments both from ocean and land, left by glaciers, which have produced landslides from prehistoric times to the present day.

Recent large flow slides occurred at Mink Creek (winter 1992-93) and Lakelse Lake in May and June 1962. A large submarine flow slide occurred in sensitive marine muds at the front of the fiord-head delta at Kitimat Arm in April 1975.

These recent landslides serve to show the continuing sensitivity of the glaciomarine sediments in the Kitimat Trough and the marine sediments on the fan-delta at the fiord-head of Kitimat Arm. Natural and human caused factors such as increases in surface load, removal of lateral support by stream bank undercutting or excavation, vibration by heavy equipment, earthquake shock, high water pressures and interruption of intertidal drainage can trigger these landslides. Thus, the potential exists for landslides to occur during pipeline construction and in the future.

This large swampy area  on Lakesle Lake is the location of the May 1962 flow slide. Highway 37 crosses the landslide depletion zone. (The highway was closed for several days after the 1962 slide.) The provincial park is in the middle left of this photo from the report.

Schwab says  the pipeline  will encounter the glacial sediments  during construction at Cecil Creek, Deception Creek, Wedeene River, Little Wedeene River, along the west side of Kitimat Arm and along Chist Creek. He says that even minor erosion along those creek banks can expose the glacial sediments, which are then displaced by as the sediments are exposed.
“Pipelines crossing glaciomarine sediments must therefore avoid areas that lie within potential flow slide depletion zones as landslides will break or disrupt pipeline service.”

The executive summary of the report concludes by saying.

Landslides travel long distances and damage linear infrastructure such as pipelines. Six large rock slides occurred in west central B.C. since 1978, five of these since 1999, and four since 2002. Three of the six rock slides severed the natural gas pipeline (Howson landslides in 1978 and 1999, and Zymoetz landslide in 2002). Damage to linear infrastructure commonly occurs in run out zones many kilometres from the initial landslide. This has occurred with recent landslides in west central B.C.; the longest traveled in excess of four kilometres along a slope of 9°. Therefore, the potential for damage to pipelines extends to unstable terrain and potential landslides that start well outside the construction corridor.

The Bulkley Valley  Research  Centre, based in Smithers, is a not-for-profit  organization that aims to improve the knowledge of resource sustainability by facilitating  what its website calls “credible research projects.”

Bulkley Valley Research Centre news release: Geomorphology report highlights pipeline concerns

James Schwab’s paper Hillslope and Fluvial Processes along the Proposed Pipeline Corridor (pdf)

This report was corrected on Oct. 25, changing the headline, correcting the main link to the Bulkley Valley Research Centre that was not visible due to a coding error and adding a link to the geomorphology report news release.

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