The Grizzly Bear Necessities

2008 ranked as one of the worst years for salmon returns on British Columbia’s central coast and the ‘silent fall’ I experienced there last year, while not surprising given the lack of fish, was disturbing nonetheless…

The silence along the river was almost deafening. No bears, or even birds, appeared along the banks. The reason soon became obvious: not a single salmon was to be seen in the glacial-fed water. Not a single salmon carcass lay on the ground, not in the estuary or the forest. There was no sign of predation and no sign of decomposition.

The usual sounds of fall in this coastal rainforest valley were agonizingly muted. The thrashing of salmon swimming upstream, the splashing of grizzlies pouncing on fish in the shallows, the cacophony of multiple bird species scavenging the bears’ leftovers—all were virtually nonexistent. And not a whiff of the fetid odor of dead and decaying salmon I have come to associate with this time of year was evident. The unnatural quiet sent a chill up my spine.

While it appears salmon returns, pink runs in particular, on the central coast are much improved in 2009, grizzly bear sightings have remained inconsistent.

The ability of grizzlies to get their quotas for salmon is really a matter of competition and the odds are stacked against the bears.  As fishermen, humans engage in what ecologists call ‘exploitative competition,’ capturing salmon en route to spawning grounds before they reach awaiting carnivores.

In a recent opinion piece for the Times Colonist, Raincoast biologists Chris Darimont and Misty MacDuffee stated that “referenced against past and current declines in salmon runs, we suspect coastal grizzlies receive a fraction of the salmon they used to, which ultimately manifests in
population declines.  Not by ‘die-offs’ as some have speculated, but through repeated years of low birth rates.  Grizzlies are omnivorous and can persist even without salmon, but they have far fewer offspring.”

Fisheries managers have always assumed that salmon exist exclusively for human consumption. Consequently, runs are only protected from harvest when they are overfished or endangered.  But how does status quo fisheries management serve the terrestrial ecosystems that salmon nourish? Not well.

As Darimont and MacDuffee explain: “Put yourself in the paws of bears.  Imagine if your big annual paycheque was reduced by four fifths.  Then imagine the effect on the coastal food web economy.  The nutrient subsidy used by the forest from the salmon carcasses, is also greatly diminished. As such, ‘protected areas’ that host highly exploited salmon runs are not really protected if a major ecological process is being compromised. Of course, it’s not just fishing nets that rob bears of this yearly bonanza.  Fish farms, climate change, habitat loss, fresh water withdrawals and changing ocean conditions all influence salmon abundance.”

So how much salmon do the bears really need? Raincoast scientists are directly addressing this question.  In hair collected from (harm-free) fur snagging stations, DNA and isotopes are used to track bear numbers, estimate how much salmon coastal grizzlies are eating and elucidate the relationship between the amount of salmon and the number of bears.  Like CSI sleuths, Raincoast is also assessing hormone levels in the hair to provide information about potential stress, reproductive activity and protein deprivation bears might show in response to poor salmon returns.  From this knowledge emerges an informed basis for action.

Did You Know?

The presence of salmon determines the size, fecundity and population density
of coastal grizzly bears.
Reproductive success for female grizzlies is directly related to their body
mass in the fall.

A version of this article first appeared in the Seaside Times November 2009 Issue.

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Coastal wolf with a salmon in its month.
Photo by Dene Rossouw.