Migrating gray whales are a common sight in the nearshore waters of the Pacific Coast, and several of the region’s national parks are whale watching hotspots. Now the timing of the gray whale migrations has shifted perceptibly, fewer whales are passing close to shore, and whale watchers will need to be more flexible.

The eastern North Pacific gray whale population numbers somewhere between 19,000 and 25,000 individuals. Although several thousand grays live year round in shallow waters in the Juan de Fuca Strait, along the Oregon Coast, and along the northern California coast, the vast majority are migratory. And boy, are they ever migratory! Gray whales undertake what is perhaps the longest migration of any mammal.

After spending the summer feeding on small crustaceans and tube worms in the Bering Sea and Chuckchi Sea (western Arctic Ocean), the grays head south to their over-wintering and calving grounds in the warm, shallow lagoons of Mexico’s Baja California. The journey south along the coast takes two or three months and covers around 12,000 miles, which is equivalent to half way around the globe. In the spring, when calves are sufficiently large and blubber-protected, the grays migrate back to their northern feeding grounds, again taking two or three months to make the 12,000-mile return journey.

Wildlife biologists aren’t sure why this migratory pattern exists, but the evidence suggests it may have developed because of predation pressure. Orcas (killer whales) prey heavily on the grays, many of which bear scars of past encounters, and are prone to attack calves when they get the chance. Sharks are also a threat to calves. By calving in the warm, protected lagoons of Baja California, the grays drastically reduce the predation risk for their vulnerable calves.

En route north, the grays swim even closer to shore and with calves flanking their mothers on the shoreward side. This makes swimming easier for the calves and reduces their vulnerability to orca attacks. (Mother grays are ferociously protective of their calves, so it’s seldom a simple matter for orcas to pick them off.)

Whale watching is a very popular activity these days, and grays are very popular with the whale watching crowd because of their habit of swimming close to shore and with little fear of humans. (Grays have been fully protected since 1946, and are about as numerous as they have ever been.) Tens of thousands of whale aficionados flock to the best shoreline vantage points during the whale migrating season.

“Whale watching” could be considered a misnomer at many shoreline observation areas. Although grays are quite large, up to 45 feet long and weighing in at 33 tons, many people watching from the shoreline don’t get to see them clearly. What they most commonly see is spouts. Before submerging, a migrating gray expels air from its blowhole several times, creating a 15-foot high spout (or blow) that is visible for four or five seconds. The spouts, produced when the whale’s warm breath condenses in the cold air near the water surface, can be seen for miles. If the whale is closer, an observer might be able to see the animal’s back, or at least its 12-foot wide flukes as it dives.

You can follow an individual whale as the pattern repeats at intervals of around three to five minutes, which is the usual time the gray remains submerged. It moves at about five miles an hour, going from right to left (north to south) during the winter migration.

Some of the best places to enjoy whale watching are situated in national parks. Two in particular – Point Reyes National Seashore in northern California and Cabrillo National Monument in southern California – are renowned for excellent whale watching.

Tens of thousands of people go to Point Reyes every year – mostly between December and May -- for the primary purpose of watching whales. The observation platform at the Point Reyes Light is actually the best place of all, but if the weather cooperates (not too much fog) many places along the headlands offer good vantage points. Whales headed south can be seen as early as mid-December, but are most numerous in January.

Few whale watching places on the West Coast are better or more conveniently located than Cabrillo National Monument, which is situated on Point Loma at the entrance to San Diego harbor. Historically, impressive numbers of grays have swum close to shore there, primarily from mi-December to mid-February. Though not as numerous as in the past (people often saw 40 an hour in the 1970s), grays passing at distances of less than a mile are still a common sight, and it isn’t unusual to see eight or more whales in an hour.

Unfortunately, the grays are more commonly staying so far out to sea that it is difficult to see them clearly. Some biologists think that the numerous whale watching boats operating in these waters have disturbed the grays and caused them to move further from shore during their migrations. Whether and to what degree the boats may have caused unwanted changes in whale behavior is the subject of ongoing research.

Speaking of research, fisheries scientists have observed that the grays recently began remaining in their northern feeding grounds about ten days longer before starting their southward migration. Just why this is so remains a matter of speculation, but the facts point to warming ocean water temperatures as the main cause.

Warmer ocean waters in the far North Pacific Ocean have disrupted nutrient supplies and changed the feeding patterns of numerous marine species. In the case of the grays, they have apparently encountered greater competition for food in the waters between Alaska and Russia and have had to move further north and feed for a longer time in order to get bulked up for the winter migration. Most grays don’t eat during the long swim south (or even while wintering in the Baja lagoons), so having adequate blubber is vital to their survival and reproductive success.

Because the grays have been departing the northern waters later than usual, they have been arriving later than usual along the shores of California. In recent years the net effect has been to shift the whale watching season about seven to ten days later.

Since it’s unlikely that the grays’ migrating behavior will revert to historical norms anytime soon, and might very well become even less predictable, whale watchers will need to be more flexible and pay more attention to reports and updates before heading off to their favorite spots along the shoreline.

It’s not yet clear whether warming ocean temperatures and related factors may adversely impact the survival rates, reproductive success, and other critical parameters of the gray whale population. It’d be a darn shame if that happened. The grays are doing better now than they have at any time since the 1850s when whalers discovered the calving lagoons and hunted the species to the brink of extinction.