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-en‐ dangered species' remark‐ able comeback from the brink of extinction.

The new research, pub‐ lished in Royal Society Open Science journal on Wednes‐ day, 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 re‐ search 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 con‐ tributed to comes amidst concerns about a large num‐ ber of the whales found dead worldwide in recent years, which scientists believe may have been caused by marine heat waves.

The new study, titled Bell‐ wethers of Change, involved 46 organizations and mod‐ elled the whales' likely popu‐ lation partly based on thou‐ sands of Northern Pacific humpback photographs - col‐ lected by nearly 4,300 "com‐ munity science contributors."

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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 extinc‐ tion in previous centuries, governments' moves to legal‐ ly protect the species - offi‐ cially 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 popula‐ tion grew quite fast, actually faster than we said was pos‐ sible," Doniol-Valcroze said. "Those populations can't grow forever, obviously, at some point they have to slow down.

"It's still a very healthy lev‐ el for a population of whales."

'They've overeaten and there'll be a correction'

According to University of British Columbia zoology pro‐ fessor Andrew Trites, the likely culprit for the change in humpbacks' fortunes is a matter of balancing their rel‐ atively rapid population re‐ covery.

"They're going to over‐ shoot initially," he told CBC News in an interview, "until they realize they've overeat‐ en and there'll be a correc‐ tion.

"What we have to watch for is if they go down, down, down again … Should we be worried and upset? It's too soon to tell."

The federal body over‐ seeing species at risk in the country, the Committee on the Status of Endangered Wildlife in Canada, now lists humpbacks as of "special concern" - because even though the species is recov‐ ering, it's still "not secure."

That's because hump‐

backs face several ongoing threats, the committee noted - such as being hit by ships, toxins, and ocean noise pol‐ lution. But "the major threat," officials warned, comes from marine heat waves reducing their food supply.

"There were changes in the environment, and in par‐ ticular a long marine heat wave," said Doniol-Valcroze. "They've been happening more and more right now in the context of climate change.

"It seems to have hit the humpback whales pretty hard. It's like the ceiling came down on them - and they re‐ acted to this by this big drop in their population."

UBC's Trites agreed cli‐ mate change is likely having an impact on humpback pop‐ ulations. But it's still unclear exactly how.

"We just have to watch to see whether or not in the long term climate change is going to reduce their food supply - or maybe it's going to improve things for them," the director of the universi‐ ty's Marine Mammal Re‐ search Unit told CBC News. "We just don't know at this point."

He noted that aside from climate change, there are the normal, periodic fluctuations in temperature to consider, such as the current El Niño cycle.

Trites praised the re‐ searchers' use of data from thousands of contributors.

"This is an amazing exam‐ ple of citizen science," he said. "And when you see so many authors on this … it's another sign of amazing leadership as well - to pull this off and have everybody put their data together for a common goal."