Humpback whale numbers have taken a dive in February, historically the busiest month of year for whales that annually breed and give birth in Hawaii’s warm waters.

Researchers at Maui’s Pacific Whale Foundation on Monday reported lower numbers in their annual shoreline whale count for the third year in a row and suggested that the peak of the whale season may be shifting.

A total of 529 humpback whale sightings were recorded Saturday during the foundation’s annual Great Whale Count. That’s 455 fewer whale sightings than last year’s total of 984, and 959 sightings short of 2015’s total of 1,488.

This year’s count, conducted in ideal weather conditions, also recorded 209 fewer pods (breeding groups) than last year’s 544 and 26 fewer calves.

“The overall decreasing trend observed since 2015 suggests that something is changing,” said Stephanie Stack, senior research biologist with the foundation.

It could be that the peak of the whale season is shifting to earlier or later in the year, Stack said, or there may be other outside factors influencing the February numbers.

Meanwhile, the Hawaiian Islands Humpback Whale National Marine Sanctuary reported seeing fewer whales in February than in January during its first annual Ocean Count of the year.

Sanctuary volunteers collected data from 44 sites on Oahu, Kauai and Hawaii island on Saturday. A total of 135 whale sightings were recorded from 10 to 10:15 a.m., the most of any time period throughout the day. That compares with 172 whales seen in January.

“Usually, there are more whales during February. It’s the peak of the season in the Hawaiian Islands,” said Cindy Among-Serrao, Ocean Count coordinator.

Among-Serrao noted, however, that weather conditions were not ideal everywhere across the islands. Counting at multiple sites on the Big Island had to be canceled due to rainfall and poor visibility.

It has been estimated that more than 10,000 humpbacks travel each year from Alaska to Hawaii, where they breed and give birth primarily between December and April, although some whales come as early as October and leave as late as June. The peak of the season stretches from January to March.

In 2016 federal authorities took humpback whales that winter in Hawaii’s waters off the endangered species list, declaring that their numbers had recovered through ongoing efforts to protect the giant mammals.

Ironically, many researchers and whale-watch industry representatives complained earlier in 2016 that fewer humpbacks were seen close to shore in Hawaii’s waters that year.

The relatively shallow waters surrounding Maui, Lanai, Molokai and Kahoolawe are the most popular destination for the wintering whales.

Pacific Whale Foundation’s Great Whale Count was established in 1988 and has employed the same criteria and data collection methods to record whale sightings.

Trained volunteers are stationed at Kaanapali, Ka­hana, Lahaina, Launiupoko, Maalaea, Papawai/McGregor Point, North Kihei, South Kihei, Wailea, Makena and Hookipa to scan the water within 3 nautical miles and record the number of pods, individual whales in each pod and any calves.

Immediately following the scan, observers devote five minutes to recording conspicuous whale behaviors, such as breaches, pectoral fin slaps, tail slaps and head slaps. This scanning cycle is repeated from 8:30 to 11:45 a.m. Each location has the same number of observers each year.

“There were even fewer conspicuous whale behaviors this year,” Stack said. “It was very quiet.”

In 2012 the Pacific Whale Foundation published a paper arguing that the annual whale counts are a valid form of citizen science that offers valuable data about population trends and patterns.

Although the number of whales has dropped since 2015, the overall trend of sightings is increasing when all of the data gathered by the Pacific Whale Foundation going back to 1995 is considered, Stack said.

More study is necessary to see whether there’s anything to the recent decline in numbers, she said. Additionally, Stack said the foundation might consider adding counts in January and March, like the sanctuary, to record trends across the season.