June 21, 2023

The Mulchatna herd was once among the largest in Alaska, with a historic range spanning from Dillingham to Bethel to Lake Iliamna. Today, the herd has dwindled to roughly 12,000; the Department of Fish and Game estimates a healthy population would range from 30,000 to 80,000 caribou.

Biologist Christi Heun is a representative for the conservation group Defenders of Wildlife. She said an ongoing study, conducted by Fish and Game biologists Nick Demma and Renae Sattler, identified two major contributing factors for the herd’s decline in a presentation last year.

“Habitat quality and disease are the two things that they’re like ‘smoking guns, this is what’s going on,’” she said.

Specifically, the study found low fat ratios in caribou mothers in the herd. Heun said this poor body condition suggests the caribou are competing for a special resource–lichen, which in the past has grown abundantly in the Mulchatna rivershed.

“We know the lichen community in the area is not as good as it used to be,” she said. “There’s encroachment from woody shrubs, as we start getting warmer summers and warmer winters.”

Biologists also recorded epidemic levels of brucellosis – a disease that can result in late-term miscarriages and weak calves. …

This May, Fish and Game undertook a month-long predation control mission, shooting 94 brown bears, five black bears and five wolves in the western subgroup calving area. The work cost approximately $415,000, according to Heun.…

But biologists like Heun say that removing predators may ultimately further the spread of brucellosis.

“The predators aren’t culling the sick animals, and so they’re leaving more sick animals on the ground to infect more animals. So the sickness is spreading,” she said. STORY

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Other lichen depletion reasons

GOVERNMENT-BACKED BROWN BEAR CULLING SPARKS CONTROVERSY

..predation is not the main reason the Mulchatna herd has declined so precipitously. Rather, biologists point to disease and lower juvenile recruitment as the primary culprits. Brucellosis, a bacterial-born illness, has recently been on the rise in the Mulchatna herd. The disease can cause pregnant cows to abort their fetuses, resulting in greater infertility in the population.

A lack of available food is equally as pressing. Caribou rely heavily on lichens as winter forage, which are notoriously slow growing. In the region the Mulchatna herd inhabits, a compilation of local knowledge reveals that lichens are not nearly as prevalent as they once were, in part due to the herd potentially overgrazing and trampling the plants when it numbered in the hundreds of thousands.

In fact, the slow decline could actually be part of the natural population arch of caribou herds, which are known to experience huge fluctuations over the course of decades (40-70 years or more). A caribou population booms, munching down the available lichens; and then crashes, once it has consumed all the food. The population then remains low for decades as lichens regrow, after which the herd size again begins to rise. In the Mulchatna herd specifically, biologists are seeing poor body condition in females, indicative of decreased forage availability.

On top of the impacts of caribou, lichens in southwest Alaska are also facing increased threats from summer wildfires and alder-brush encroachment on the tundra and alpine areas where they grow. In all, it’s a perfect storm of a population downturn combined with disease. SOURCE]