Oregon State University researchers working in Alaska’s Bristol Bay have now documented what has been obvious to many bear biologists for a long time: small salmon streams are important to big bruins.
Forget those iconic photos of grizzlies snatching salmon from the falls at the McNeil or Brooks rivers. According to the work of Johnathon Armstrong and colleagues, the streams a full-grown grizzly can jump across appear more important.
“Small populations of salmon (contributed) roughly half of total bear consumption while representing only one‐fifth of total salmon escapement,” they reported after studying the Wood River drainage in Southwestern Alaska.
Their study has implications for both development and commercial fisheries in the Bay region and potentially throughout Alaska.
“The stream spawning sites that our model represents are often 3 kilometers (1.9 miles) or less in length and can be challenging for fish to access even in their undeveloped state,” an appendix to the study noted.
The streams themselves averaged only about 12-feet wide. Their widths and depths offered the salmon less protection from bears than is found in the region’s big rivers.
“Salmon populations that spawn in small tributary streams are far more vulnerable to predation than populations that spawn in rivers or on lake shores,” the authors reported, and for this reason “empirical studies of bear–salmon interactions suggest that some small salmon populations can contribute disproportionately to the foraging opportunities of bears.”
When the scientists modeled the salmon consumption by bears in the drainage, they concluded that ensuring significant numbers of salmon reached small streams made two to three times as many fish available to the region’s grizzly bears.
With their study, Armstrong and colleagues were clearly aiming at the proposed and highly controversial Pebble mine to the east.
“We feel it is reasonable to assume that watershed development such as mining could degrade, dewater, or fragment these (small stream) sites in ways that eliminate the salmon populations they support,” the appendix concluded. “Indeed, analysis of sockeye salmon in the contiguous United States found that approximately 50 percent of populations have been extirpated by humans and this may be a conservative estimate because populations were defined at a coarse resolution that would often not detect the finer scale extirpations we simulated.”
But the study’s findings extend beyond mining into the management of commercial fisheries in the 49th state.
“Increasing (salmon spawning) escapement from the average level observed (1.5 million over 56 years) to two‐times the average (3 million) only increased consumption by 15 to 31 percent,” the scientists reported. “In contrast, at the average observed escapement level, increasing the phenological variation from our minimum to maximum simulated value increased bear consumption by 52 to 75 percent.”
That “phenological variation” – the climate-related differences that dictate where and when various salmon stocks spawn – is tied to early arriving Alaska salmon, according to the study.
“Populations returning to small streams also spawn the earliest due to colder temperatures,” the study reported, “and may be the only salmon available for a substantial window of the salmon‐foraging season (for bears).”
Protecting early returns of salmon to the state’s rivers has historically been a low priority for the Commercial Fisheries Division of the Alaska Department of Fish and Game, especially when large salmon runs are forecast.
Kenai River 2011
On the way to the fourth-largest commercial salmon catch in 20 years in upper Cook Inlet, the state agency in 2011 allowed commercial fishing to continue even when it was obvious the early return of sockeye to the Kenai River was extremely weak.
“In 2011, sockeye salmon harvests in the central district up to July 14 were well below average, especially in the upper subdistrict set gillnet fishery,” the end-of-season harvest summary would later note. “The July 14 cumulative harvest of 269,000 fish was more than 43 percent lower than the average harvest of 475,000 fish from 2000 to 2010.”
The situation in-river was even worse. With the commercial fishery harvesting most of the early return, less than 64,000 sockeye had passed a Kenai River sonar counter as of July 15 – about 28 percent of the average number of fish in-river for that date in the previous decade.
Those fish help feed the 2,200-square-mile Kenia River drainage, an area about twice the size of the state of Rhode Island.
When it comes to bears, early returns to the drainage are somewhat buffered by a commercial fishing closure through most of June designed to ensure early-run sockeye for the hook-and-line fishery on the Russian River, a major Kenai tributary. But the Russian return, like the early Kenai return, was weak in 2011.
Slightly more than 29,000 sockeye were counted through a weir in the river by July 15. That was at the bottom range of the escapement goal of 22,000 to 42,000. Escapement is the number of salmon escaping fishermen to win the chance to spawn.
State commercial fisheries managers cannot be blamed for the low numbers. Getting significant numbers of sockeye into the Kenai River early has never been a priority in what is a very complicated fishery.
Fisheries managers have historically tried to concentrate on catching as many sockeye early as possible so as to minimize the time commercial nets are in the water later in July when a highly prized run of Chinook salmon shows up.
The big “kings” as they are called in Alaska have been the focus of a decades-long battle between commercial fishermen on one hand and anglers plus Kenai tourists businesses on the other. The kings are by-catch in the commercial fishery, but the most-prized catch for Alaskans and visiting anglers.
Caught in the middle
The bears might, in part, be paying a price for this battle, according to the new study.
When it comes to feeding bears, the scientists concluded, both the size of salmon runs and their timing matter, and above a certain level timing appears to matter more.
In the Wood drainage “at a threshold of approximately 2 million salmon, adding additional escapement had little effect on bear consumption, whereas phenological variation could still increase bear foraging by nearly 50 to 100 percent (compared to a situation with homogeneous run timing),” the researchers reported. “The effect size of phenological variation increased with increasing salmon escapement. In combination with the saturating effect of escapement, this generated two domains in the response of bears. At high salmon abundance, bear consumption was primarily sensitive to phenological variation, whereas at low salmon abundance, bear consumption was primarily sensitive to escapement levels.”
The short version is this: The more salmon filling little creeks in Alaska, the more bears.
Only this being Alaska, the question of whether that is a good thing or a bad thing is also open to debate. Issues have already arisen on the Kenai Peninsula and in Anchorage, the state’s largest city, as to how many bears are too many bears.
In the city, where several people have been killed by bears and many more injured, the issue is primarily public safety. Outside the city, the focus is more on predation.
Boosting bear numbers means more hungry bears emerging from their dens in the spring with sometimes little around to eat but winter-weakened moose and their calves. A state study of bears in the Nelchina Basin north of Anchorage found them killing an average 34.4 moose or caribou calves per year over the 45 days at the start of the Alaska summers from 2011 to 2013.
That is not a problem in areas where moose populations are large, but in areas where moose populations are low, such high kill rates can keep those populations from recovering for a long time.
Ecosytem management – something about which environmentalists have long talked – is probably so little practiced because of its complexity. There are a lot of tradeoffs.