anchovy drought may turn these giants around

2 humpbacks making their way up delta
Agencies try to keep wayward whales, boats clear of each other
by Glen Martin, Chronicle Staff Writer Tuesday, May 15, 2007

Two wayward humpback whales forged their way up the Sacramento River on Monday, evoking the visit 22 years ago of the Bay Area's most famous marine mammal, Humphrey the humpback whale.

The animals are by far the largest creatures on the river, naturalist Stan Minasian of the Oceanic Society said after viewing videotape of them swimming in the opaque waters of the Sacramento-San Joaquin River Delta. He estimated their length at 50 to 55 feet, and their weight "at about a ton per foot."

Doreen Gurrola, the assistant director of the Marine Mammal Center in Sausalito, confirmed the two animals are humpbacks after a review of videotape but said it is not clear if both of them are adults. "One seems a little smaller and could be a juvenile," she said. "We also think one may be injured. There seems to be something attached near its dorsal fin -- maybe an entangled net."

By late Monday afternoon, the whales were reported 4 nautical miles north of Rio Vista in Solano County, said Lt. Amy Marrs of the U.S. Coast Guard. The National Marine Fisheries Service, which has authority over marine mammals, is expected to confer today with local agencies about whether to attempt to persuade the whales to swim back down the river.

Their presence in the delta is an extraordinary event, Minasian said. "It's very rare to see them in the bay, and almost unheard of to have them in the delta," Minasian said.

The only other record of a humpback in the delta is Humphrey, Minasian said, a whale that spent 26 days exploring the region in 1985 before it was finally driven back to the bay and the ocean with acoustic devices. Humphrey returned to San Francisco Bay in 1990, ran aground on a mudflat north of Sierra Point near Candlestick Park, was pulled off with a cargo net and again was sent seaward with noise-makers.

Minasian said humpbacks, which are migrating off the Pacific Coast this time of year, have "no business" being up the delta. "These are big, pelagic animals that normally are off the Farallones at this time of year, feeding heavily on fish such as anchovies," he said. "They have convoluted migration routes, and they exhibit very sophisticated behavior."

Humpbacks typically feed by working together in groups. Individuals will synchronize the exhalation of air bubbles to force schools of fish into tight, compact masses. When the fish are packed together, the whales charge into them with mouths agape. "It's an amazing thing," Minasian said. "Each individual knows its role in the feeding strategy and executes it perfectly."

The two humpbacks could turn around on their own accord, whale experts said, because of the profound dearth of a main food source -- anchovies -- in the Sacramento River. "They're going to get hungry, and there's nothing for them to eat up there," Minasian said. "At a certain point, they should follow the tidal water back to the bay and out to the ocean."

But it might be wise to help the process along, he added, as boat traffic is the greatest threat to the whales. "Right now they're a hazard to navigation, and navigation is a hazard to them," said Minasian.

"Humphrey attracted a huge number of boats, and the same thing will probably happen to these animals. The water is murky, and it's hard to see where they are. Accidents can happen. We should probably try to convince them to leave the area sooner rather than later."

It's not particularly difficult to get humpbacks to move in a preferred direction, Minasian said. "They're acoustically sensitive animals," he said. "They don't like noise. By creating noises that are uncomfortable for them, it should be fairly easy to direct them downriver."

Authorities are taking precautions to protect both the humpbacks and boaters. Vessels are precluded from coming within 100 yards of the whales, said Marrs, and aircraft should remain at an altitude of at least 1,000 feet when in their general vicinity. The Coast Guard is providing Marine Safety Information bulletins on the humpbacks' locations at VHF-FM Channel 16.

When the humpbacks were first spotted Monday, many observers assumed they were gray whales, smaller cetaceans that visit the bay with some regularity. A study conducted by the Oceanic Society from 1999 to 2001 determined that gray whales filter in and out of the bay year-round, except in August, Minasian said. Most visits occur from March through May, when the animals are migrating from their birthing lagoons in Mexico to their feeding grounds off Alaska. The number of gray whale visits seem to be particularly high this year, Gurrola said, based on the number or reported sightings. Jack Dumbacher, curator of birds and mammals at the California Academy of Sciences in San Francisco, said he recently spotted a gray whale in the Raccoon Strait between Sausalito and Angel Island. The bay and delta are more congenial habitats for grays than humpbacks. Grays will take a variety of prey opportunistically, but they generally are bottom feeders, rooting around in the mud or silt for crustaceans and other small organisms.

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This article appeared on page B - 1 of the San Francisco Chronicle
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