On Tuesday, a headless, badly-composed whale washed ashore along the Point Reyes National Seashore in northern California. It was the 12th dead whale to wash ashore since March along the northern California coastline.

The whale at Point Reyes rolled in with the surf just 3 few days after a 28-foot juvenile gray whale washed up Saturday on Portuguese Beach in Sonoma. Less than week earlier, on May 19, a gray whale washed up in Half Moon Bay, just as officials in Pacifica were burying two other beached whales – a humpback and a sperm –that had recently beached there. Another gray whale was found on a Mendocino County beach last week, and in April, two gray whales came ashore in Santa Cruz County while a killer whale was found near Fort Bragg.

At least one of the big mammals showed evidence of being hit by a ship – something not uncommon in this area, where more than 7,000 vessels enter the Golden Gate each year alone. Two other whales were found to have missing limbs, an indication that they may have been attacked by orcas or become entangled in fishing gear. What is puzzling to scientists though is that some were very young, and others appeared to be very old. Across all the species of whales found washed ashore, there appears to be no singular cause, or even a single common one found so far.

The number of whales found will likely decrease now, as the annual gray whale migration is coming to an end. Most grays have passed the California shoreline by the end of May. During this time, most baleen whales move from their winter breeding grounds in low latitude and warmer waters to their summer feeding areas in higher latitudes with cooler waters. The migration route of the Pacific Gray Whale is often described as the longest known mammal migration in the animal kingdom. Beginning in the Bering and Chukchi seas and ending in the warm-water lagoons of Mexico’s Baja peninsula, their round trip journey completes over 12,000 miles. As ice forms in the arctic, Gray Whales begin their journey south. By mid-December to early January, the majority of the Gray Whales are usually found between Monterey and San Diego, where they are often seen from shore.

Gray Whales can reach a length of 46 feet and a weight of up to 36 tons (72,000 pounds). At birth calves are about 15 feet long and weigh close to one ton (2,000 pounds).

Not a record 

In 1999 and 2000 there was a large die-off of gray whales along the Pacific Coast from Mexico to Alaska. There were 283 dead whales found in 1999, and 368 in 2000. This alarming number of strandings was 8 times what was normally seen. In Puget Sound, WA a similar pattern of strandings emerged, with over 50 gray whales stranded between 1999 and 2000.  This was almost eight times the normal average. Before that die-off, there were approximately 26,600 gray whales nationwide, according to estimates by the National Marine Mammal Laboratory in Seattle.

Fortunately, in 2001 and 2002 the number of strandings along the Pacific Coast dropped significantly to only 20 animals each year. It is unknown why so many whales died between 1999 and 2000, but many of the animals who died were severely emaciated (starving). One possibility is that the gray whale population was too high and there was not enough food available to them.

Ship Strikes

Many species of whales and dolphins are vulnerable to collisions with vessels, and that’s especially true near the Golden Gate, Long Beach, and San Diego ports. The ports of Los Angeles and Long Beach, San Diego, San Francisco Bay Area, Portland, and Seattle together service more than 50% of all container ship traffic coming to and from the United States. In the Golden Gate area alone, more than 7,000 vessels pass through each year. Collisions with large vessels often either go unnoticed or unreported, particularly for the smaller species. As a result of this, all vessels 65 feet (19.8 m) or longer must travel at 10 knots or less in certain locations along the U.S. east coast at certain times of the year to help reduce deaths by ship strikes (and reduce damage to ships as well).

In the fall of 2007, 4 blue whales were struck and killed by ships and found in or near the Santa Barbara Channel and Channel Islands National Marine Sanctuary. Three years later, between July and October 2010, two blue whales (one pregnant female that resulted in the loss of the fetus), one humpback, and two fin whales were found dead in and around Monterey Bay, Gulf of the Farallones, and Cordell Bank National Marine Sanctuaries. Accordingly, mortality from ship strikes has been identified as a threat to population recovery of these vulnerable whale species.

Killer Whales

Killer whales are a likely culprit in some of the recent deaths, and suspected in the latest carcas to was ashore at Pt. Reyes. The orcas congregate around Monterey Bay and ambush mothers and their calves as they attempt to cross the deepwater canyon there. The violent drama, involving fleeing whales and pursuing packs of orcas, is an annual extravaganza of death that scientists say has been growing in intensity as the number of whales and orcas increase.

Killer whales tend to hunt in groups, like wolf packs. With sharks, orcas may herd them to the surface and strike them with their tail flukes, while bottom-dwelling rays are flushed out with bubble-blowing before being cornered and pinned to the ground and taken to the surface. Killer whales can induce tonic immobility in sharks and rays by holding them upside down, rendering them helpless and incapable of injuring the whale. Some sharks suffocate within about 15 minutes while the whale holds them still, because these sharks need to move to breathe.

Killer whales attack gray whales, and especially target their more vulnerable calves. They will attack in their packs, biting and slamming whales with their tails, and drowning the calves. They will also ram the gray whales in an attempt to weaken them, and particularly try to separate the calf from its mother. A photographic essay on this behavior can be found here.

 

Scientists Puzzled, Not Worried

With the recent standings, scientists are looking at a variety of factors, including environmental changes, food distribution, shipping and predator behavior. And while the cluster of deaths is odd, it’s not record breaking.

“I don’t necessarily think that this is unusual,” Justin Viezbicke, the stranding coordinator for the National Marine Fisheries Service in Long Beach, said. “We should anticipate seeing some whales on the beaches. That is a part of coastal California life. They provide for a lot of critters.”