LIHU'E, Kaua'i — The first humpback whales of the season were spotted off the west and south shores of Kaua'i, about a week earlier than initial sightings of the past two years.

"Exciting — the beginning of the season," said Dave Matilla, science and rescue coordinator with the Hawaiian Islands Humpback Whale National Marine Sanctuary. "It's pretty early, but not out of the norm."

Blue Dolphin Charters Capt. Dave Kalthoff said he saw a whale Friday afternoon off Lawa'i Kai on the southern coast of Kaua'i while he was operating the 65-foot catamaran Blue Dolphin.

"It was a single juvenile, maybe 18 to 22 feet long. It breached in front of me twice," he said. The crews aboard two other boats in the area also saw the whale, he said. Kalthoff, a captain for seven years, said he had no doubt the animal was a humpback.

Two days later on Sunday, passengers and crew aboard the tour boat Na Pali Explorer 2 saw what they believe were two humpbacks between Miloli'i and Nu'alolo valleys on the Na Pali Coast.

"We're pretty sure there were two, but we never saw them both at the same time. One did a full breach out of the water and we got a pretty good look at it," said Kimberly Anderson, a Na Pali Explorer crew member. "It breached twice and we think it was the same whale both times. It seemed to be a yearling, not that big."

Matilla said females and young whales are normally the first humpbacks to return from the Arctic feeding grounds each season. An estimated 5,000 humpback whales visit Hawai'i annually to socialize, mate and calve in the Islands' warm, shallow waters. The majority of the whales arrive by mid-December and most leave by April. Matilla said the ones that arrive earliest also tend to leave Hawaiian waters early.

"The earliest tend to be females with calves from last year, or juvenile animals one or two or three years of age," he said.

A whale sighted off Wai'anae in August, initially thought to be a humpback, was later identified as a sperm whale.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.