Porcupine Herd caribou swarming the North Slope of the Brooks Range/U.S. Fish and Wildlife Servic photo

Once more there is talk of oil development in the Arctic National Wildlife Refuge (ANWR), and once more there is worry of a threat to the Porcupine caribou herd which calves in the refuge, and once more there is the debate about what past oil development has meant to Arctic caribou.

And so far overlooked is the latest research that suggests a lot of the data around which this debate swirls could be largely meaningless.

In a study published in Applied Ecology in April, a team of scientists led by Per Fauchald, the senior researcher for the Norwegian Institute of Nature Research, reported their examination of migratory tundra caribou in North America has led to the conclusion the species has a “cyclic, or quasi-cyclic fluctuations with a periodicity in the range of 40 to 90 years.”

If that is true, much of the study conducted on Alaska Arctic-slope caribou could be tracking natural, cyclic variations in population rather than any changes related to oil development.

Over the course of the last 39 years, the population of the Central Arctic Caribou herd, which ranges in and around the Prudhoe Bay oil fields, has gone from about 5,000 animals, up to 70,000 animals, and then back down to about 23,000, according to the Alaska Department of Fish and Game. 

Population cycles are a well-documented wildlife phenomenon in North America.

“…Investigations into population cycles shaped the development of Anglo-American animal ecology during the 1920s-1930s,” wrote ecologist Susan Jones in the Journal of Historic Biology this year. “Population cycling revealed patterns that challenged ideas about the ‘balance’ of nature; stimulated efforts to quantify population data; and brought animal ecology into conversation with intellectual debates about natural selection. (Charles) Elton used the problem of understanding wildlife population cycles to explore a central tension in ecological thought: the relative influences of local conditions (food supply, predation) and universal forces (such as climate change and natural selection).”

Fauchald and his team have suggested that broad climate variations – one of those “universal forces” of which Jones writes – and not local conditions – such as displacement of caribou due to oilfield development – could be the main factor driving caribou numbers in the long run.

The Norwegian scientists reported a “paradoxical decline in caribou populations” tied to a greener Arctic richer in plant resources in recent years. The decline appears to influence caribou populations in undeveloped areas as well as those in developed areas.

The counter-intuitive conclusion in the study warrants a little explanation.

Warmer = greener

Greener on the human-dominated planet of the 21st Century is usually thought of as gooder. And there is little doubt that the northern reaches of  the northern hemisphere have been slowly but steadily growing greener since the late 1800s. 

There has been a steady push of shrubs onto the tundra and in the wave behind the shrubbery new forests. This sort of growth would be expected to increase plant biomass.

Using “data obtained from the Advanced very High Resolution Radiometer sensors onboard the National Oceanic and Atmospheric Administration satellite series,” the Norwegian scientists said they were able to measure just such an increase in biomass.

They thought this might increase Arctic carrying capacity for caribou, but they concluded that it did just the opposite.

“…The climate-induced greening had a negative impact on caribou population growth,” they wrote. ” This result suggests that the climate-induced greening was accompanied by a deterioration of pasture quality, possibly through a change in the composition and availability of forage plants. It is well established that the greening of the Arctic is mainly attributed to the expansion of tall erect deciduous shrubs in the Arctic tundra biome. In North America, expanding shrubs such as birch and alder contain antibrowsing toxins (resins) that deter browsing from mammals.

“These shrubs respond readily to climate warming, and because the antibrowsing defense gives them a competitive advantage over the more edible Salix (willow) species, they dominate the shrub expansion in several areas, replacing moss-, grass-, and herb-dominated vegetation. Moreover, the expansion of shrubs reduces the lichen cover, which is an important winter forage for caribou. In summary, the current shift to a shrub-dominated tundra might therefore reduce the availability of high-quality caribou
forage.”

How exactly this change is destined to play out on the ground over tens of thousands of square miles of Arctic wilderness going forward is a big unknown. It could make the North Slope of the Brooks Range, which shrubbery has yet to reach, even more important to the calving of the Porcupine caribou herd.

But it could also mean the opposite.

If a warming climate reduces the overall carrying capacity of the 78,000-square-mile range of the Porcupine herd, a high birth rate on calving grounds might just lead to a lot more calves starving.

“If a herd is too large for its habitat, animals become nutritionally stressed,” according to the Alaska Department of Fish and Game. “Cows generally have fewer calves and survival of both calves and adults decreases. Population peaks also tend to coincide with high parasite loads and disease susceptibility.”

Big country

The Porcupine herd roams a big, empty land the size of the Czech Republic that stretches east from Alaska’s Colville River into the Yukon and Northwest Territories of Canada.

The herd now numbers close to 200,000 animals, about twice its population in 1977, according to the Alaska Department of Fish and Game. 

Most calves were once thought to be born in May and June on Alaska’s North Slope in a 2,500-square-mile area between the Katakturuk and Kongakut rivers just south of the coastal village of Katovik. Researchers tracking radio-collared caribou in recent years have found a much less predictable pattern.

Starting in 2004, ” large portions of the herd calved along the Canadian border in
Ivvavik National Park, Canada,” Fish and Game’s latest annual report on the Porcupine herd details. A move back towards Alaska started in 2012 and peaked in 2016 when most of the caribou were again calving in ANWR.

And then this year the caribou were spread out “on the coastal plain from the Sadlerochit Mountains, Alaska to Babbage River, Canada,” according to Fish and Game.

Some of the caribou calving grounds overlap potential oil development areas in ANWR; others don’t. Caribou are absent from areas of potential oil fields in winter.

Winter-only drilling operations have been suggested to minimize the impacts on caribou, but questions have been raised about disturbing denning female polar bears although there are indications that forward-looking-infrared (FLIR) search technology and dogs might make it possible to identify den sites and keep development away from them.

Damage done?

Whatever the case going forward, much of the debate sure to come in the nation’s capital as the Trump administration pushes toward opening ANWR drilling is likely to focus on the past.

“…In longterm studies of the Porcupine herd (named after the Porcupine River in the Yukon and Alaska), (researcher Chris) Johnson found that even decades after oil development in the Canadian portion of its range, caribou were still avoiding areas within 6 kilometers of roads and wells,” Warren Cornwall wrote in Science Magazine this week.

Johnson is a wildlife ecologist at the University of Northern British Columbia in Prince George, Canada. Johnson’s studies date back 13 years, a blip in time if caribou cycles are operating on a 40 to 70-year basis. 

But Johnson did a pretty good job of framing the most important question in the whole debate: what does development mean at a population level?

“We get into a more nuanced conversation,” he said “‘Does this mean there are going to be a lot fewer caribou, [or] a little fewer? What [development] means for population dynamics is the million-dollar question.”

Some, of course, would contend the options should be broadened to include a lot fewer, a little fewer or possibly more.

The effect of existing, North Slope oil field development on caribou populations remains much debated, and because of that the oil-field-roaming Central Arctic herd has been closely monitored for about four decades.

Research has been generally inconclusive. Supporters of oil development for years touted the growth the of the herd. Now, with the herd in rapid decline since 2010, environmentalists spotlight it.

Studies have shown female caribou move away from roads to calve. Studies also show the number of calves killed by predators declines because roads bother wolves and grizzly bears more than caribou.

The herd, which numbered only about 5,000 animals when oil development began at Prudhoe Bay, grew to peak of 70,000 animals in 2010.

“From 1997 to 2008 CAH (Central Arctic Herd) increased at an impressive 10–13 percent annually,” notes the Central Arctic Caribou Herd News from the Alaska Department of Fish and Game. “ADF&G biologists attributed this increase to high pregnancy rates, good calf survival, and low adult female mortality.”

Then came a significant decline in female survival. Biologists concluded some of the die off was to be expected given a large number of old females in the population, but they conceded late springs in 2013 and 2014, which delayed green-up and the availability of good food, might have contributed.

Whatever the driver, the herd started shrinking fast. By 2016, “a new census indicated that the herd was less than half of the size it was in 2010,” having fallen to 22,630 caribou, according to Fish and Game.

But caribou deaths weren’t the only thing going on.

“From 2013 to 2015, extensive mixing occurred between the CAH, Porcupine, and Teshekpuk (caribou) herds after calving and during the winter,” state wildlife biologists reported. “Several thousand caribou left CAH and joined other herds.”

Exact numbers are unknown, but the wildlife researchers had enough radio collars on CAH caribou to determine that the departures were significant.

Oil field development could have helped the caribou, hurt the caribou or – if the Norwegians are right – done little to help or hurt as the caribiou population naturally fluctuated.

Unpredictable animals

As far back as 1991, David Klein of the University of Alaska Fairbanks and others were theorizing that the truly important swings in caribou numbers might be occurring over long, long time spans. But they lacked for data to support the theory.

“Caribou populations fluctuate widely over long periods of time and the possibility that
caribou populations cycle with a periodicity of 65 or more years has been proposed,” he concluded in a presentation to the Fifth North American Caribou Workshop, later published in Rangifer in 1991. “Unfortunately, estimates of population numbers of specific herds are reliable only during recent decades, therefore no adequate data sets exist upon which to test this hypothesis. To be cyclic, fluctuations in numbers must have a common periodicity.”

He also noted the inherent difficulties in anyone predicting what caribou population of might do. In so doing, Klein pretty much threw under the bus the much-beloved idea of a “balance of nature” wherein prey – like caribou and moose – live in some sort of comfortable harmony with predators – like wolves and bears.

Klein was willing to accept that might happen somewhere, but Alaska wasn’t that somewhere.

“At high latitudes, climatic extremes with interannual variations result in wide fluctuations in plant productivity and availability as forage, as well as having direct effects on survival of young, predator-prey interactions, levels of insect harassment, and energetic costs of locomotion and thermoregulation,” Klein wrote. “Consequently, wide fluctuations in numbers of caribou is common as is also true of many other northern herbivores, such as lemmings, hares, and ptarmigan.”

Alaska’s Mulchatna caribou herd numbered less than 40,000 animals in the early 1980s and was located in a contained area north of Iliamna Lake west of Anchorage surrounding the site of the proposed Pebble Mine.

The herd started growing late in that decade and exploded into the 1990s.

By 1996, its population had increased to about 200,000, and it’s range had expanded west hundreds of miles to the coast of the Bering Sea and north to Kuskokwim River. Then came the big crash. In less than a decade, the herd size was back down below where it had been in the 1980s.

The latest count puts the herd’s population at less than 30,000. The decline might have been blamed on Pebble – if the Pebble project had begun. It hasn’t and might never. And yet the Mulchatna herd declined anyway.

Over-used range, parasites and predators have all been blamed. It’s complicated.