North Pacific humpback whale numbers fall by 20%, but some scientists aren't worried yet

A sprawling international study of humpback whales in the northern Pacific has found their population has shrunk significantly since 2012 — despite the once-endangered species' remarkable comeback from the brink of extinction. 

The new research, published in Royal Society Open Science journal on Wednesday, estimated a roughly 20 per cent drop in the cetacean species' numbers over a decade.

But despite that, one of the study's nearly 75 listed authors said the findings are not yet cause for alarm.

Thomas Doniol-Valcroze is head of the cetacean research program for Fisheries and Oceans Canada's Pacific Biological Station.

"It's not catastrophic news just yet," he told CBC's On the Island in an interview. "But it certainly it took us by surprise."

The research he contributed to comes amidst concerns about a large number of the whales found dead worldwide in recent years, which scientists believe may have been caused by marine heat waves. 

The new study, titled Bellwethers of Change, involved 46 organizations and modelled the whales' likely population partly based on thousands of Northern Pacific humpback photographs — collected by nearly 4,300 "community science contributors."

Precise counts of the giant but elusive marine mammals are near impossible.

"It's not like we can count them all ... but we're pretty confident in those trends," Doniol-Valcroze said.

He explained that after being hunted to near extinction in previous centuries, governments' moves to legally protect the species — officially outlawing commercial hunting in 1976, when their population was estimated to be at most 1,600 — allowed them to make a remarkable rebound.

By 2012, Northern Pacific humpbacks' population had exploded to what scientists believe was more than 33,000.

"Once we stopped killing those animals … the population grew quite fast, actually faster than we said was possible," Doniol-Valcroze said. "Those populations can't grow forever, obviously, at some point they have to slow down.

"It's still a very healthy level for a population of whales."

According to University of British Columbia zoology professor Andrew Trites, the likely culprit for the change in humpbacks' fortunes is a matter of balancing their relatively rapid population recovery.