As gray whale mothers and calves journey up the West Coast toward summer feeding grounds it’s becoming increasingly clear that this is a special season. As in baby boom!

The number of calves on their first-ever migration from Baja California nursing grounds to the Arctic has astonished whale watchers and landing operators, and represents a welcome sight for researchers hoping Pacific gray whales will rebound after several recent low-production years.

Gray whale calf greets admirers in a Baja California lagoon before its first-ever journey to Arctic feeding grounds. Credit: Diane Alps

“At this rate we just might exceed our record high of 222 cow/calf pairs by May 15,” said Alisa Schulman-Janiger, director of the ACS-LA Gray Whale Census and Behavior Project at Point Vicente on the Palos Verdes Peninsula.

Through Tuesday, volunteer spotters at Point Vicente had logged 181 calf sightings, marking the third-highest count since the project began in 1984. The record was 222 was in 1997.

It’s too early to predict whether this will be a record-setting year, but it will be one of the top calf-production years since spotting stations were established, beginning with the ACS-LA project.

The boom occurred most likely because of a meager Arctic ice cover last spring, which enabled pregnant females early access to important feeding areas. “In years that ice is slow to melt, primarily in April and May, pregnant females cant get to the feeding grounds,” explained NOAA Fisheries biologist Wayne Perryman. “They’re bumping up against this ice trying to get to feeding areas but they can’t get far enough north. So when ice is slow to recede the odds of their pregnancies going to term are reduced.”

Gray whale mothers and calves are still passing California and Oregon, trailing pregnant females, adult males and juveniles. Cow-calf pairs require more time to complete the 6,000-mile return migration and they generally hug the coastline, providing research stations with ideal vantage points.

At Point Piedras Blancas in Central California, Perryman, who leads NOAA’s Cetacean Health and Life History Program, has reported single-day sightings of 28 cow-calf pairs on two days during the past week.

Twenty-eight is the most for one day since 2004, when 456 calves were counted by the end of what turned out to be the second-biggest production season since the program began in 1994. (501 calves were sighted in 1997.)

Through Tuesday, about halfway through the cow-calf peak migration period off Central California, Perryman’s spotters had tallied 192 calves. They expect many more over the next couple of weeks.

“You want to be in the 300s at the end of the season — those are good calf years,” Perryman said.

Last year, spotters counted 255 calves. In 2010 and 2009 they counted only 71 and 86, respectively.

Pregnant females fast during the four-month round-trip migration, so they require steady nourishment from the moment they reach the Bering and Chukchi seas. Their diet consists of small crustaceans such as amphipods and tube worms, found in bottom sediments.

“When they get back up north they need to start putting on fat right away because next year they’re going to have a calf and they’re going to lactate and feed that calf while they’re fasting again next year,” Perryman said. “So if you’re not a fat girl you’re probably not going to make it.”

The Pacific gray whale population numbers about 20,000. It has edged upward since devastating mortality events between 1998 and 2000, following poor feeding seasons. During that period the population dropped from about 28,000 to about to 18,000 whales.

Gray whales, which were once hunted to the brink of extinction, were removed from the endangered species list in 1994.

– Top two images are courtesy of Diane Alps. Bottom two are courtesy of Searcher Natural History Tours