As Hawaii’s 2021-2022 humpback whale season gets underway, scientists say they hope to see population numbers continue to recover after an estimated 50% plunge in 2015-2016.

The migratory cetaceans swim 3,000 miles from Alaska to mate, give birth and nurse their calves in Hawaii waters from November through March.

“We saw an almost 80% decline in mother-calf pairs and a 39% decline in adults between 2013-14 and 2017-18 in Maui waters,” said Rachel Cartwright, founder of the Keiki Kohola Project, a nonprofit humpback whale research center. Declines off Maui, Kauai, Oahu and the Big Island were also reported by researchers at the Pacific Whale Foundation and the National Oceanic and Atmospheric Administration’s Hawaiian Islands Humpback Whale National Marine Sanctuary, as well as boaters, fishermen and citizen whale counts from shore.

According to a 2020 report on the national sanctuary’s website, the decline was triggered by a “trifecta” of warm-water events in 2013-2016 that heated Alaska waters up to 5 degrees Fahrenheit above normal. The condition caused the food source in the feeding grounds for the whales to vanish, preventing many from building up the fat stores they need to survive during their trip to Hawaii. The whales abstain from food throughout their migration.

Reproductive rates dropped as fewer whales made the trip to the islands and, possibly, because fertility declined.

“Because the hormones that stimulate ovulation come from fat, it’s very likely females didn’t go into the normal, two-year reproductive cycle,” Cartwright said.

Then, in 2019-2020 and last winter, there was good news.

“The warm water dissipated, food stocks improved and by 2019 we were seeing lots of mums and calves on Maui, and by 2020 those numbers were right back up to 2014 levels,” Cartwright said in a phone interview.

But “we aren’t out of the woods,” she warned, noting that humpback whales face the stress of steadily warming seas due to climate change, as well as boat strikes, noise, entanglement in fishing gear and other man-made problems.

And, while a dramatic uptick in whale numbers was observed in 2019-2020 by survey vessels off West Maui, rising from 2,207 the previous season to 2,826, last season’s numbers dipped back to 2,207, as reported in a paper by researchers Eden Zang and Marc Lammers of the sanctuary.

“Results indicate that after the reported period of decline in whale presence, the number of humpback whales using the west Maui area has generally increased, but has fluctuated over the three seasons surveyed,” the paper stated.

There have also been fluctuations in the timing of migration, said Lammers, who measures whale density off Maui, Kauai, Oahu and the Big Island with visual surveys and underwater microphones that measure decibel levels of the males’ mating songs.

“In (spring) 2019 we saw an earlier end to the season, with relatively low numbers by March compared with January and February,” Lammers said in a phone interview, “and in 2020 there were even better numbers in February that persisted into March, in a kind of extended season, while in 2021, (numbers) peaked in February but had a rapid decline in March.”

In 2015-2016, the season their numbers plunged, the whales also arrived in Hawaii significantly later than usual, said Ed Lyman, natural resource specialist for the sanctuary, who manages responses to entangled, stranded and otherwise distressed whales.

“In late December 2015 I was getting Maui tour boat operator reports saying, ‘The whales are pretty late this season,’” Lyman said, noting the season is normally well underway by November; “and when I checked with the different islands and started doing transects (surveys), they confirmed it.”

Cartwright pointed out that last season’s numbers were lower than in 2013, the last year the humpback population, estimated at 8,000 to 12,000 whales, was still growing.

The Hawaii and other humpback whale populations had been steadily increasing due to protection under the 1970 U.S. Endangered Species Act and a 1985 final moratorium on commercial whaling.

Because of this growth, in 2016 nine populations of humpback whales were delisted from endangered status. They remain protected by the federal Marine Mammal Protection Act.

The timing of the whales’ arrival and departure from Hawaii waters, Cartwright and Lammers said, is crucial for the development of newborn calves, who must consume an estimated 12-15 gallons of milk a day in order to grow big and strong enough to survive the trip to Alaska.

“An extended breeding season is a good sign that the population is probably well fed, which should translate to successful calf rearing,” Lammers said, whereas “shortened breeding seasons can be a sign that whales are having to prioritize more time finding food at higher latitudes, possibly due to scarcity, (which) could mean fewer females coming to Hawaii to breed and consequently little reason for males to linger longer, or having to return to Alaska to feed earlier.”

Cartwright said aerial footage taken with drones showed that while mothers and calves were of normal, oblong shape, many nonparent “escort” whales appeared emaciated, with “about a 15% dip in body volume.”

Even if numbers resume their rise, she and other researchers warn that in the long term, if global temperatures continue to rise, the health of the whales and the oceanic ecosystem in which they play a critical role will decline.

“What’s concerning is that the ocean is getting warmer consistently, and they’re estimating by 2050 it will be 1-2 degrees Fahrenheit higher, plus these warm- water heat-wave conditions are likely to keep occurring,” Cartwright said.

Three possibilities might result, she said: Females might lower their reproductive output and calve less frequently during periods of nutritional stress; mothers might alter their migratory routes as food sources shift; and calf survival rates may be changing for the worse.

While there have been few studies to date, Cartwright said, estimated first-year survival rates for calves had been 82% before dropping closer to 70% in 2010.

She added that last season, for the first time, she witnessed apparent aggression toward a calf by a male escort in aerial footage shot by a drone.

“The calf was a neonate; there were remnants of placenta in the water,” she said. “(At first) the mom’s got the calf riding on her back, and as the male approaches the calf, the mom moves the calf to her other side.”

While she can’t draw any conclusions from this single incident, Cartwright said whale researcher Nicola Ransome has reported “a little bit more aggressivity” by escort males toward mother-calf pairs in other whale populations around the world.

Researchers at the Keiki Kohola Project “need to look at whether or not calves all survive their time on Maui, and take on the task of tracking our moms back to Alaska,” Cartwright said.

Other research on mother- calf nursing pairs, including video shot via small tag sensors attached to calves, is being conducted by Lars Bejder of the Marine Mammal Research Program at the University of Hawaii at Manoa Institute of Marine Biology.

Meanwhile, rather than await the results of ongoing, long-term studies, Cartwright and other scientists say, it’s crucial that humans take care now to reduce stress our activities can inflict on the threatened whales.

Earlier this year the Pacific Whale Foundation on Maui published results of a three-year study on the effects on whale behavior by whale-watching vessels, and provided voluntary guidelines in addition to federal laws that boats cannot approach within 100 yards of whales, said Jens Currie, chief scientist of the foundation’s domestic research program.

“If you’re looking for whales, slower is better,” he said, because of the impact engine noise might have on whales’ behavior, in addition to the greater potential of hitting a whale when a boat is going faster.

“You should reduce speeds to 6 knots or less within 400 yards” of whales, Currie said, and “also just slow down in general to 15 knots or less when cruising around.”

“Maui waters are a very busy place, and moms and calves swim right through the harbor, and we have boat strikes, entanglements and injuries,” Cartwright said.

“I’d emphasize (giving whales space) to all ocean users,” she added. “We’ve really seen the strongest reactions to kayaks in mothers and calves — they bolt from kayaks, maybe confusing them with predator shapes.”

The more humpback whale calves survive, Cartwright added, the more this “critical bio-indicator species” can support the ocean food chain and mitigate against warming oceans by providing a crucial carbon sink.

The whales feed at depth, she said, then rise to the surface, into nutrient-poor waters, where they defecate iron-rich poop.

Iron supports the phytoplankton the krill feed on, and the krill feed the humpback whales and other ocean life.

And, “The more whales you have, the more poop you have, so the more phytoplankton growth you have, and phytoplankton are a carbon sink, like forests on land.”

All the more reason to protect them, Cartwright said, as humpback whales improve the odds of our own species’ survival.

For more information on Hawaii humpback whales, visit hawaiihumpbackwhale.noaa.gov, pacificwhale.org and mmrphawaii.org.

CITIZEN WHALE SCIENTISTS

Every winter, volunteers with the Hawaiian Islands Humpback Whale National Marine Sanctuary’s Sanctuary Ocean Count on Kauai, Oahu and Hawaii Island, and the Pacific Whale Foundation’s Great Whale Count on Maui, compile whale sightings from shore on the same day in January, February and March.

The 2022 Ocean Counts are scheduled for the following Saturdays: Jan. 29, Feb. 26 and March 26.

For more information and to volunteer, visit hawaiihumpbackwhale.noaa.gov/involved/ocean-count and pacificwhale.org/research/community-science/great-whale-count.

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Mindy Pennybacker, Star-Advertiser