Several caribou herds in Alaska's Arctic are on the decline. That now includes the Porcupine herd, which is the largest. Biologists say the reasons for the downward trends are hard to pin down.
Alaska Department of Fish and Game announced this week that both the Porcupine and Central Arctic caribou herds have faltered. That's on top of a drastic decrease for a large Western Arctic Caribou herd, which the department announced in December.
Mark Nelson, a wildlife biologist with the department, monitors the herds in Interior Alaska, but he says he is aware of the broader trend.
"The general consensus is that a lot of these herds, especially Arctic herds, are declining at the moment," Nelson said. "But what that means as far as the future, or what's driving it, I really don't know."
The Porcupine herd roams across the eastern part of Alaska's Arctic and into Canada. It is only hunted by the Arctic Village residents and fly-in hunters, Nelson said.
The herd was among a few that were considered to be thriving after reaching an all-time high during its last count, eight years ago. But this year's census showed that the population had decreased by about 75,000 animals — from 218,000 caribou to 143,000 — which is more than 30%.
Nelson said the news was not a surprise to biologists monitoring the herd, but they needed a census for confirmation. That's not an easy feat for a herd that migrates between two countries.
"We were all pretty sure we were in some level of decline, and that's based on things like adult survival, calf survival, parturition rates – like the rate at which those females are giving birth," he said. "But because it had been so long since we had a photo census, it's really hard to know exactly what was happening."
Nelson said that throughout the last eight years, biologists have noticed that younger cows have been giving birth to fewer calves compared to the older females. They also saw fewer calves overall.
Nelson said that "there's clearly no smoking gun," and it's hard to single out one reason for the trend.
"It can be nutrition, it can be predators," he said. "The 'why' is hard for us to understand and to figure out, but it does seem like calf survival is a driver of this decline right now."
Biologists expect to see a few more years of decline before the Porcupine herd stabilizes again, Nelson said.
"It's just kind of part of these natural increases and decreases over time," he said.
The Central Arctic Caribou Herd is a smaller herd that migrates in the central part of the North Slope, around Deadhorse. Its population also dropped this year. The new count is 26,600 animals, which is a decrease of over 20%.
That herd has also seen lower calf and cow survival, according to the press release from the department.
Animals in the Central Arctic herd are hunted by people from the North Slope communities of Nuiqsut and Anaktuvuk Pass as well as Wiseman residents and some Alaskans who drive up the Dalton Highway from Fairbanks.
Nelson said he doesn't anticipate any changes to hunting regulations this year.
There are more than 30 caribou herds across the state, though seven of them include the majority of the animals, according to data from the U.S. Fish and Wildlife Service. Many of the herds have been shrinking or not growing in recent years.
Across the Arctic, caribou herds have declined by 65% over the last three decades according to the Arctic Report Card, released by the National Oceanic and Atmospheric Administration in 2024.
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