Judge halts grizzly hunting because Yellowstone bears need to find more diverse sex partners

The grizzly bears are spared from hunting, for now. 

For as low as $600 per hunting permit, grizzly bears were scheduled to be legally hunted in Wyoming beginning on Sept. 1, making it the first such hunt in over four decades. But after first just temporarily suspending the hunt, a federal judge has now bucked attempts by the U.S. Fish and Wildlife Service to remove the Yellowstone-area grizzlies from the endangered species list.

The , however, wasn’t about hunting. It was about how this isolated population of some 700 bears requires influxes of fresh genetic material to remain biologically resilient in the years ahead. This detached bear population, Chief District Judge Dana Christensen determined, were too biologically vulnerable to be removed from the infamous list. 

“The real point is, the judge is correct. There is a real problem here,” Eric Hallerman, who researches the genetics of wildlife species at Virginia Tech, said in an interview. 

“I am so surprised that a judge is so well-versed in science that he sees this,” Hallerman said.

A female grizzly bear, or sow, in Yellowstone National Park.

It doesn’t matter that there’s now a growing population of around 700 healthy bears in this area, which inhabit the unprotected areas in and around Yellowstone National Park. (Though, this is unquestionably a huge improvement from 1975, when biologists estimated a population of between 136 and 312 bears.)

The problem is that this population of grizzly bears is isolated. And when a population is isolated, genetic diversity is lost over time — it’s inevitable. Through a process called genetic drift — one of the foundations of evolution — certain genes in a population are passed down more than others.

This is especially the case in small populations as they “will lose genetic diversity just by chance as individuals carrying rare forms of a gene die or fail to reproduce,” Faith Walker, who researches wildlife genetics at Northern Arizona University, said over email. 

Even if there were considerably more than 700 grizzlies in the population, the bears would still fall victim to genetic drift.

“It’s not really a numbers game,” Kristin Brzeski, a wildlife ecologist with an expertise in conservation genetics at Michigan Tech, said.

“You could have 1,000 of them, but eventually they will lose genetic variation due to drift if there’s no infusion of new genetic variability,” she said. 

“It makes it very hard for this population to keep projecting itself forward,” said Hallerman.

There’s an obvious fix, however: new bears from other populations, like the 900 bears living in and around Glacier National Park, mating with bears living in Wyoming. Yet, in the modern U.S., the wilderness is fragmented by cities, towns, highways, fences, and swaths of developed land. This puts a hitch in the natural flow of genes.

“You need animals to move and disperse so they can adapt to changing climates and habitats,” said Brzeski. “And that doesn’t exist — they can’t move to Glacier and back.”

In the lower 48 states, the grizzly bear range is just a fraction of what was, centuries ago.

There’s no question the climate is changing. On the more local scale, for bears, that means adapting to changes in their diet and the diseases they’re exposed to, said Brzeski.

“The big thing is to be able to adapt,” she said. “Things are changing.” 

The closest grizzly bear population to these isolated Yellowstone-area bears is Glacier, more formally known as the Northern Continental Divide Ecosystem. Yet as Christensen noted in his ruling, “there is no evidence of interbreeding” between these two populations — or any U.S. grizzly populations. The Glacier bears, at the closest points to the Yellowstone population, are still 70 miles away and divided by Interstate 90. 

A judge dissects the science

From the judge’s written decision, he appears disappointed, if not frustrated, with the federal government’s understanding of the science behind these grizzly populations.

Quoting from two grizzly population studies that were used by the Department of Fish and Wildlife Service (which oversees the Endangered Species Act) in its attempt to delist the bears, Christensen emphasized that “without an adequate gene pool, the Greater Yellowstone grizzly bear will be at increased risk of endangerment.”

In fact, the judge found that the federal agency “misread” this very research.

“The Service illogically cobbled together two studies to reach its determination that the Greater Yellowstone grizzly population is sufficiently diverse at this time,” Christensen wrote. “In doing so, it ignored the clear concerns expressed by the studies’ authors about long-term viability of an isolated grizzly population.”

The expanded grizzly bear range expanding outside of the Greater Yellowstone Ecosystem between 1990 and 2016.

Today, these 700 grizzles are clearly a conservation success story, as they’ve grown and been closely managed for decades under the watch of the Interagency Grizzly Bear Study Team. This scientific agency, led of the U.S. Geological Survey, did not have an expert available this week to comment on this story.

Yet, allowing this still-recovering population to be hunted almost certainly won’t help its cause. Hunts, though carefully managed and require permits, will further diminish the bears’ gradually dwindling genetic pool — even though they’re healthy today. 

“That doesn’t mean they can withstand anthropogenic gunshot fatalities on top of these other factors,” said Brzeski. 

What’s more, the unfolding circumstances in this Yellowstone-area bear population “don’t occur in a vacuum,” said Walker, noting that other grizzly bear ecosystems, like that around Glacier, also would benefit from a diverse gene flow from the Yellowstone bears. 

But how to exchange these genes remains a problem. Perhaps it can be done naturally, if the bears are given routes, or corridors, between their segmented populations.

“The jury’s still out on whether corridors can be promoted to let these grizzlies do their own match dot com,” said Walker. “Dispersal via such corridors doesn’t have to happen very often to have a big genetic impact.”

Over a decade ago, the federal government considered transporting in other wild grizzlies to buttress the gene pool in 2020, should the bears still not naturally accomplish this on their own.

For now, it appears these Yellowstone-area bears — protected again by the Endangered Species Act — are on their own genetically, fenced in by modern society. 

“This population is now on its own evolutionary trajectory,” said Hallerman.