A 12,000-mile trek: Gray whales moving through Monterey Bay – The Mercury News

MONTEREY — This time of year, gray whales are making their annual southern migration from Alaska and are cruising through Monterey Bay on their arduous journey to their calving grounds in the lagoons of Mexico.

But scientists are watching the pods closely following last year’s significant mortality rate of the 35-ton marine mammals. Their 12,000-mile trek is an annual ritual that packs the whale-watching boats moored to Old Fisherman’s Wharf in Monterey as well as Moss Landing and Santa Cruz.

It is the longest mammal migration of any species on Earth.

The migration of on average 27,000 whales got off to a bit of a slow start this year but is now picking up momentum, allowing scientists and nonprofit groups dedicated to protecting the whales let out a collective sigh of relief, according to land-based observers on the coast of Rancho Palo Verdes.

There was some concern because of the abnormal amount of fatalities that occurred during last year’s southern migration, said Alisa Schulman-Janiger, who runs the annual Gray Whale Census & Behavior Project from the Point Vicente Interpretive Center in Rancho Palos Verdes.

The southern migration historically peaks along the Central Coast in mid-January. By mid-March, with calves in tow, the pods will turn north for their migration to the Bering Sea where they summer. During the entire migration, north and south, the whales do not eat — a total of two months.

The hope is that they foraged longer in their northern feeding grounds and will be healthier as they make their migration, potentially rebounding after a year in which they were skinny, starving and washing up dead in large numbers along the entire West Coast

The fatalities led the National Oceanic and Atmospheric Administration in May to declare an “unusual mortality event” over concern for the species. Necropsies — animal autopsies — were conducted on some of the whales, with findings indicating many were emaciated, according to NOAA.

It is too soon to draw any conclusions from such a small sampling of sightings off the coast of Rancho Palos Verdes, said Dr. Bruce Mate, professor emeritus at the Marine Mammal Institute at Oregon State University. Sightings, he said, could depend on factors such as weather. Storms can drive pods farther from shore, out of sight of land-based observers.

Mate said there are a number of explanations as to why the number of fatalities jumped last year, but the one he puts the most stock in has to do with the amount of food available in the northern feeding grounds compared to the current population of whales.

“Right now just leaving the feeding grounds they are in the best condition of the year,” Mate said. “We don’t expect to see many fatalities now.”

But that can change by the time they reach Mexico and begin the trip back, having not eaten since early winter. The emaciation seen last year is a signal of inadequate nutrition that Mate and others believe is due to the number of grays outstripping the food supply. The 27,000 gray whales today is similar to the number before the advent of commercial whaling.

While in the feeding area in Alaska, the whales contend with a strong urge to begin moving south. But Mate said that without enough calories on board, a host of problems will emerge. One of the results is that female grays are unable to carry the fetuses to term because of insufficient body mass.

It is the same phenomenon in humans when female distance runners have such lean body mass they are unable to get pregnant. Some are unable to menstruate at all.

“The body just says ‘that is not going to happen.’” he said. “And if the (grays) do get pregnant they often will abort the fetus.”

The number of deaths last year could be nature’s way of adjusting for the food supply, Mate said.