Whale sightings down due to warming seas
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.
US and international researchers, wildlife managers and federal officials were meeting in Honolulu on Tuesday and Wednesday to discuss the decline in sightings of humpbacks that traditionally migrate each autumn from Alaska, where they feed during the summer months, to Hawaii, where they mate and give birth during the winter.
Data presented at the meetings shows 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 Nino period in 2016, and a massive “blob” of warm water in the region.
The Pacific Decadal Oscillation, a current that switches between cool and warm periods over the course of many years, switched to warm in 2014.
Data shows that “it was more favourable for the whales when we were in a cold period, and then less favourable 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 survival as well as juvenile survival,” Gabriele said.
“I think there are metabolic issues that are probably related to the production of a calf. 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 spreading out or moving north to cooler waters to find their prey, which could explain why there are fewer sightings in Hawaii.