Food chain disruption eyed in Hawaii whale sighting decline
Researchers unclear whether this points to long-term change
HONOLULU — Research into the decline of humpback whale sightings in Hawaii points to a food chain disruption likely caused by warmer ocean temperatures in the whales’ feeding grounds in Alaska, federal officials have said.
U.S. and international researchers, wildlife managers and federal officials were meeting in Honolulu Tuesday and Wednesday to discuss the decline in sightings of humpbacks that traditionally migrate each autumn from Alaska, where they feed during the summer, to Hawaii, where they mate and give birth during the winter.
Data presented at the meetings show a strong correlation between warming oceans and the missing whales, said Christine Gabriele, a federal wildlife biologist who monitors humpbacks at Glacier Bay National Park in Alaska.
Three factors have warmed the ocean in Alaska since 2014, the same year scientists noticed a decline in sightings in Hawaii.
There was a change in an ocean current known as the Pacific Decadal Oscillation, a warm El Niño period in 2016 and a massive “blob” of warm water in the region.
The Pacific Decadal Oscillation, which switches between cool and warm periods over the course of many years, switched to warm in 2014.
Data show that “it was more favorable for the whales when we were in a cold period and then less favorable when the (Pacific Decadal Oscillation) switches to warm,” Gabriele said.
“In Glacier Bay, we have definitely seen a much lower calving rate and much lower calf, as well as juvenile, survival,” Gabriele said. “… We’re not clear if it’s a lack of pregnancy or lack of ability to carry it to term.”
The whales may also be moving north to cooler waters to find prey, which could explain the fewer sightings in Hawaii.
Based on the latest largescale population study, it is estimated that half of all North Pacific humpbacks journey to Hawaii each year, putting the total number of whales making the 6,000-mile round-trip migration at around 11,000 annually.
If they are forced to find new areas to forage, they could be finding new areas to breed, possibly in areas that are not as closely monitored as the main Hawaiian Islands where the decline has been most notably observed.
And while scientists agree that a decline in sightings in both Alaska and Hawaii is because of a change in food, they don’t know if there is a larger issue that could be impacting the entire habitat.
Officials with the National Oceanic and Atmospheric Administration hope this week’s meetings will help them form a plan and get funding to help ensure the species’ continued success.
“At least in Alaska, there’s something happening with the prey,” said Marc Lammers, research coordinator for NOAA’s Hawaiian Islands Humpback Whale National Marine Sanctuary. “What we didn’t really resolve is whether that applies more broadly … across the North Pacific.”
The researchers said that while historically there have been dips in sightings on specific islands in Hawaii, those declines were usually accounted for by an increase in sightings elsewhere in the archipelago.
But over the past four years, there has been an “unprecedented” drop of between 50-80 percent in sightings across the entire main Hawaiian Islands.
“There is no question that the world is changing, the oceans are changing,” Lammers said. “The humpback whales are reflecting those changes and we now need to try to understand whether this is something that will eventually correct itself, and time will tell, or whether this is something that points to a more sustained change.”