Scientists hope to solve caribou mystery

Tobias Romaniuk
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Strategy attempts to discover why herds declined and are now rebounding

There are many unanswered questions about what caused the rapid decline of caribou populations in the 1990s, and part of the problem is that the answer is not simple.

The caribou strategy, a five-year study of animals on the island portion of the province which began in 2008, is supposed to explain the decline and devise a way to help caribou populations recover.

Shane Mahoney, a research biologist and executive director for sustainable development and strategic science with the Department of Environment, is leading the project.

He said understanding the current situation requires looking back nearly a century.

The current population arc is a repeat of what happened between the 1890s and 1920s, when the number of caribou fell from an estimated 100,000 to 15,000.

The wolf disappeared, coyotes were scarce and hunting was banned. Despite this, the caribou didn’t begin to recover until the 1960s.

“What is often missed (is) the period between the peaks, how long it took before the population started to increase,” said Mahoney.

Caribou have a relatively conservative reproductive strategy; they have only one calf, no matter how much food is available, even in captivity.

From the 1960s to the 1990s, herd populations steadily increas­ed, peaking at 100,000 animals. By the mid-1990s, the population began to decline again, with a 60 per cent drop in population from 1999 to 2009.

Estimates place the current population around 32,000.

Some herds, such as the Avalon and Grey River herds, showed declines of more than 90 per cent.

What caused it? The answer involves a complex web of factors, and pointing to any one cause as the definitive answer isn’t easy.

“Single causes are very difficult to explain satisfactorily for what takes place in a system such as this,” said Mahoney.

Predators, food supply issues and the condition of the caribou all play a part.

“There are these layers of interaction between variables, which is a whole part of the reason, of course, that we developed this very elaborate scientific approach and a strategy to try and tease these various pieces apart,” he said.


Few calves survive

A progress report, written by Mahoney, states that while the underlying cause of the decline is unknown, research shows predation led to low calf survival rates.

“Whether this high rate of predation mortality is primarily due to changes in predator populations (increased populations, the arrival of coyote to the island) or to changes in vulnerability of the calves (smaller or weaker calves), or some combination, is unknown,” the report says.

Also contributing to the decline is evidence that suggests the caribou population is outgrowing its habitat.

“Although the body of evidence is consistent with a density-dependent decline … the root cause of the population decline remains elusive,” states the report.

It would appear from the evidence that a population of 100,000 caribou is too large for the forests of Newfoundland to support. But they can support more than 32,000.

Between those two figures is a sustainable population number, which Mahoney and his team of researchers are still trying to determine.

“What is a reasonable population that might be maintained in the long term that perhaps does not experience these extreme highs and lows? This is one of the central questions for the caribou strategy to answer,” he said.

Changes in antler and jaw bone size, pregnancy rates and other indicators are used to determine the health of a herd, and from that data a sustainable population number is developed.

“But bear in mind it’s never a fixed point,” Mahoney cautioned.

Figuring out and achieving that sustainable population will require the management not only of caribou, but of predator populations, such as black bears, coyotes and lynx.

“We really are taking a system approach here, and we’re studying the bears, we’re studying the coyotes, at the same time that we’re studying the prey.”

The first step in achieving a sustainable caribou population is to halt the population decline.

The problem is, insufficient calves are surviving. Still, based on the research since 2003, the calf survival rate has increased somewhat, said Mahoney.

From 2003 to 2005, the survival rate was from zero to five per cent.

“We need about 45 to 50 per cent survival of calves to get our population rising again,” he said.

Now some herds are at 35 per cent, Mahoney said, but while the numbers are rising, they still aren’t enough.

The improved survival rate did not occur as a result of direct intervention, Mahoney added.

“One could safely and honestly say that the improvement that has come in calf survival has happened, to an appreciable extent, by natural factors.”

That brings Mahoney back to one of the central questions of the strategy: how did the calf survival rate become so low in the first place, and what changed to reverse the trend?

The answer may lie in the massive amount of data that has been collected in the past few years. The caribou strategy is moving into a data-analysis stage and it is hoped some answers will be found.

The results will be compiled in a report to the provincial government that is expected to be completed in eight to 10 months, said Mahoney.

What they do know about the caribou population, though, provides some hope for the future.

“We still have the healthiest populations of woodland caribou that exist,” said Mahoney.

“It’s a long way from the 95,000-100,000 we had, but these animals that we have today, the (30,000 or so), they are healthy, they look very good now, their condition is excellent and their pregnancy rates are good. They’re producing good numbers of calves, so the population is healthy.”

Twitter: tobiasromaniuk

Organizations: Department of Environment

Geographic location: Grey River, Newfoundland

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