Category: Science Magazines

More coastal salmon spawning helps grizzlies and fisheries

From Conservation Magazine, a short article on our recent PLoS Biology article:

Letting more salmon escape fisheries along the coast could boost both grizzly bear populations and fishery yields, according to a new study in PLoS Biology.

Fishery managers already let a certain number of salmon slip away so those fish can spawn. But it’s not clear which “escapement” level is best for the fisheries and the ecosystem. Grizzly bears eat salmon and often leave the remains of their meals by streams, providing nutrients for plants and animals. And the number of spawning fish also affects fishery yields down the line.

Researchers tackled the problem by modelling the effects of different escapement levels for four coastal sockeye salmon stocks and two inland stocks in Alaska and British Columbia, Canada. In the coastal systems, leaving more salmon to spawn would increase bear density by 8 to 44 percent. Fishery yields would jump as well — “an apparent win-win situation,” the authors write.

Read the full article here.

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Let Them Run

From Conservation Magazine, a nice little article on our recent paper in Conservation Letters calling for a small number of fully protected salmon runs.

Ask not what a park can do for spawning salmon. Ask what robust salmon runs could do for the park – and for coastal fishing communities.

That’s the provocative idea behind a “radical” proposal being floated by a group of conservation biologists. Limiting fishing for some pink and chum salmon bound for spawning streams in British Columbia parks could reinvigorate ecosystems that thrive on the annual infusion of millions of fish carcasses. And, in the long run, protecting the runs could produce economic benefits by making ecosystems more productive and resilient to change.

“Although managers safeguard protected areas for migratory species, little consideration has been given to how migratory species might benefit parks,” a team led by Chris Darimont of the University of California, Santa Cruz, and the Raincoast Conservation Foundation in Canada write in Conservation Letters. Case in point: Headwaters streams in coastal parks in British Columbia once saw huge annual runs of Pacific salmon. Many of the spawned-out fish died, producing a “fertilizer effect” that pumped a vast pulse of nutrients into surrounding ecosystems. “The breakdown of salmon carcasses…  ultimately can affect communities of riparian plants, terrestrial and freshwater invertebrates, resident fish, and songbirds,” the authors note. These days, however, commercial and recreational fishers kill up to 90% of the fish before they can spawn, blocking the transfer of nutrients.

To restore at least part of that pulse, the authors propose limiting catches of pink and chum salmon(Oncorhynchus gorbuscha and keta), which have still have large runs but low commercial value. While Chinook salmon sold for $1.23 a pound in 2002, for instance, pink and chum sold for just 6 to 16 cents a pound. “We believe that a focus on pink and chum… provides opportunity to implement our ideas without severe economic consequences.”

The authors concede that “some might deem our idea politically unachievable,” but add that their “aim is to inform and inspire decision-makers with a plan that not only favors biodiversity but also one that ultimately might yield economic and management benefits. Our goal is to inoculate the literature with a provocative idea to stimulate discussion.”

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Top 100 Stories of 2009

Discover magazine listed our PNAS article as #30 on its list of top 100 science stories of 2009.

Humans are powerful agents of evolutionary change: Wild animals and plants that are hunted or harvested evolve three times as quickly as they would naturally, according to a study from the University of California at Santa Cruz. In our quest to bag the biggest and the best, we introduce selective pressures that favor less desirable creatures, such as those with smaller bodies or less majestic horns. Hunting also gives a competitive advantage to animals that have babies when they are younger, before they become tempting targets for humans.

A team led by biologist Chris Darimont combed through data on dozens of species—predominantly fish but also bighorn sheep, caribou, marine invertebrates, and two plants. (“Hunters also want the biggest ginseng,” Darimont says.) Animals that are routinely subject to pursuit are, on average, 20 percent smaller and reproduce at a 25 percent younger age than what would be expected without human influence, the researchers determined. Predation is not the only way that people affect populations. Creatures that are exposed to environmental influences like pollution also experience accelerated evolution, although the effect is less dramatic.

The resulting changes have ripple effects, Darimont notes. Smaller and earlier breeders often produce fewer offspring, for instance. “Size really matters,” he says. “If a harvested animal keeps shrinking, it may no longer be prey to its predator. The whole food web can be altered.”

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The Fastest Way to Change a Species: Start Eating It

From Science magazine, more coverage on our PNAS article.

From the dwindling Atlantic cod to the increasingly rare American ginseng plant, species are racing to adjust to relentless human exploitation. According to a new analysis, the rate at which hunted and harvested species are changing their size and breeding schedules is unmatched in natural systems. Ecologists say the results point to errors in the way we manage fisheries and other harvested populations.

Researchers have noted rapid changes in heavily exploited fish and other species since the 1970s. To name one famous example, adult Atlantic cod (Gadus morhua) have decreased 20% in size over the past 30 years, and females now reproduce a year earlier than they used to (ScienceNOW, 31 January 2007). Although such hunting-induced alterations seem rapid, evolutionary biologist Chris Darimont of the University of Victoria in Canada, and colleagues wanted to determine whether they outpace changes in nonharvested organisms.

Read the full article here.

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Wolves Buffer Scavengers Against Climate Change

From Conservation Magazine, a story about our PLoS Biology article documenting the influence of wolves on scavengers as the climate changes.

Wolves and other top predators may help other species cope with climate change. Milder winters in Yellowstone National Park mean fewer elk (Cervus elaphus) die late in the season, which is tough on bald eagles (Haliaeetus leucocephalus), grizzly bears (Ursus arctos), and other scavengers that depend on the carcasses.

New research shows that wolves help scavengers by killing elk and thus providing more late-winter carrion. “Wolves act to retard the effects of a changing climate on scavenger species,” say Christopher Wilmers and Wayne Getz of the University of California, Berkeley, in PLoS Biology.

Many scavengers — from ravens (Corvus corax) and bald eagles to grizzly and black bears (Ursus americanus) — rely on carrion to get them through the winter in Yellowstone. However, without gray wolves (Canis lupus), carrion got scarcer as late winters got milder because deaths of elk depended primarily on snow depth. But after wolves were reintroduced in 1995, they once again became the primary cause of elk death and thus carrion availability.

To see whether wolves could buffer the impact of climate change on late-winter carrion, Wilmers and Getz analyzed 55 years of weather data from northern Yellowstone National Park, which has the park’s largest elk herd (at perhaps 10,000) and nearly 100 wolves. The researchers then estimated carrion availability with and without wolves by using models that accounted for factors including snow depth, wolf pack size, and elk kill rate as well as changes in the wolf and elk populations.

The weather analysis showed that Yellowstone’s winters have gotten shorter and milder, with shallower snow in the late winter months of March and April. The models confirmed that wolves do buffer the impact of milder winters on carrion availability: late-winter carrion drop-ped sharply as temperature increased without wolves but largely rebounded with them. Specifically, March elk deaths declined 27 percent without wolves vs. only four percent with wolves; April elk deaths declined 66 percent without wolves vs. only 11 percent with wolves.

“Late winter carrion in Yellowstone will decline with or without wolves, but by buffering this reduction, wolves extend the timescale over which scavenger species can adapt to the changes,” say Wilmers and Getz. They are now testing whether scavenger populations are in fact higher in areas where wolves have been reintroduced.

This work also shows that there is no substitute for intact ecosystems. “Their conclusions challenge the notion that human hunting serves as a surrogate to wild carnivore predation. Wolves distribute carrion widely in time and space, whereas modern human hunters do not,” says Douglas Smith of the National Park Service, who leads the Yellowstone Wolf Project.

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