This week’s Georgia Straight cover story looks at environmental destruction in the Pacific Northwest as part of a global phenomenon scientists are calling the “sixth extinction”.

The growing consensus is we have entered a new epoch wherein human activities are causing plants and animals to disappear at a rate that’s occurred only five times in the planet’s last 500 million years.

This places Homo sapiens in very violent company. The best known and most recent of those five previous mass extinctions occurred roughly 65 million years ago, when an asteroid struck the Earth with such force it brought an end to the age of the dinosaurs.

According to a July 2014 paper published in the academic journal Science, around the world, 322 vertebrate species have gone extinct since 1500 and another 16 to 33 percent of surviving vertebrates are now classified as threatened or endangered.

Just as troubling, B.C. scientists told the Straight, is what we don’t know.

The same report notes that of the estimated 1.4 million invertebrate species, scientists have assessed less than one percent. Of that small portion, 40 percent are considered threatened, which means hundreds of thousands of invertebrates could disappear before we are even aware they are at risk.

Chris Darimont, science director with Raincoast Conservation Foundation and assistant professor at the University of Victoria, recently expressed concern for similar knowledge gaps in an interview with the Straight about the province’s annual grizzly bear hunt.

He argued that while B.C. grizzlies are not classified as at-risk or endangered, the hunt is a concern because the province is issuing licences for people to kill the animal without knowing exactly how many live in the region.

“That grizzly-bear hunt, in most places in the province, is done in the absence of fieldwork that examines if there really are the number of grizzly bears that [government] models say there are,” he explained.

A Ministry of Environment website states that in 2012, there were approximately 15,000 grizzly bears in B.C. Darimont countered that rigorous population estimates have only been conducted in about 12 percent of the province.

From 1993 to 2012, hunters in B.C. killed 5,241 grizzly bears, according to data supplied by the province for an article the Straight ran on April 1.

“In particular with grizzly bears, we ought to be concerned,” Darimont said. “Being high up on the trophic web, there are fewer of them, and so we have to proceed very carefully. And not only are there fewer of them, but they reproduce generally more slowly than the herbivores, and they come into contact with humans and they usually end up dying as a result of that conflict. So there are a whole bunch of reasons why we ought to be careful.”

John Alroy, an associate professor in the department of biological sciences at Macquarie University in Australia, is one of world’s foremost experts on that sort of slow but steady decline Darimont argued should prompt caution.

On the phone from Sydney, Alroy similarly called attention to how much we don’t know about how quickly animals are disappearing.

“There is not actually a really solid answer to the question, ‘How many species have gone extinct in the last century?'” he said. “It is very hard to prove that something is actually extinct, just because you haven’t seen it lately. You are trying to prove a negative. And all you need is very tiny population of a species and it is not extinct.”

Even for large mammals now relatively well protected, rates of decline can be difficult to detect, Alroy continued.

Generally speaking, he said, large mammals such as bears have relatively long gestation periods as well as longer intervals between pregnancies. In addition, they give birth to smaller numbers of offspring, and those newborns take longer to grow to maturity.

It all adds up to a slow reproductive rate, which means a population can only lose a small number of members each year—even a number undetectable without close observation—before it enters a state of decline.

“It seems like there is still the same number of animals around because they [a group of humans] haven’t really knocked off that many,” Alroy said. “But then they keep on doing this for hundreds or thousands of years, and then eventually you run out.”