Volunteers counted 811 humpback whales — an average of two every 15 minutes off O'ahu and Kaua'i and an average of three humpback whales every 15 minutes off the Big Island — during this weekend's annual Hawaiian Islands Humpback Whale National Marine Sanctuary Ocean Count.

The number of whales counted was lower than previous years but many counting sites had to shut down because of high winds, rain, blowing sand and rough waters, according to Christine Brammer, who coordinates the sanctuary ocean count.

"Normally February is when we see the most whales, typically at least double what we had," Brammer said. "It's so weather dependent."

Some 650 volunteers collected data from 55 sites statewide on Saturday. Studies have shown that Hawai'i's humpback whale population has been increasing at an annual rate of approximately 7 percent, according to the National Oceanic and Atmospheric Administration.

Another Sanctuary Ocean Count is scheduled for March 28.

In a separate count conducted on Maui yesterday by the Pacific Whale Foundation, volunteers sighted 1,010 whales.

Intermittent showers and gusty winds hampered the efforts of more than 200 volunteers at 13 sites along the south and west shores of Maui, and on the northern shore at Ho'okipa.

The count on Maui was significantly lower than the record 1,726 sightings reported last year, when conditions were clear and sunny.

Foundation president Greg Kaufman said there is a two-year cycle, with fewer whales counted in odd-numbered years. There were 959 whale sightings in 2007.