Gray whales, Eschrictius robustus, spend nearly all of their time within 12km of the shoreline, so they are one of the most commonly viewed whales by humans. They are medium-sized whales. Females may grow to be 25-30,000kg and 15m in length (add 5000kg if the female is pregnant). Males are a bit smaller at 20,000kg and 13m long. Despite that bulk, we rarely see more of them than the vapor of their spouts at the surface. They empty their lungs of 600 liters of air and grab another breath in 2 seconds.
From June through October Grays are in the Bering Sea, feeding around the clock. Grays are baleen whales, or mysticetes. Instead of teeth they have a row of baleen on each side of the mouth that is fibrous tissue and acts as a filter for feeding. “Mysticete” comes from the Greek word for “mustache.” The baleen resembles a mustache when the whales mouth is agape. Amphipods, tube worms and other tiny invertebrates thrive on the seafloor which is rich in nutrients and stoked by arctic summer sunlight. Grays dive to the bottom (no more than 70m deep) and suck up a mouthful of prey and mud. They use their tongue to press the water and mud through the baleen, leaving the food items to be swallowed. During their 5 month feast an adult may consume 60 tonnes seafood and have a weight gain of some 3000-6000 kg.
Gray whales don’t all migrate at once. The first group to go south are the pregnant females, starting in mid-October. The males and other females join in around mid-November. Even then, they don’t really travel in distinct social groups. They are solitary. It is more like a bunch of individual whales that happened to be traveling along the same route to the same place. Grays swim virtually non-stop at 7km/hr for 2 months straight to cover the 10,000km trip south. When sleeping they rest one hemisphere of the brain at a time. In this way they are able to swim (and breathe) during sleep. They burn about 23kg of fat stores per day. Put another way, they get about 16 miles per gallon of fat (a tractor-trailer rig gets about 8mpg).
Half of the females trekking to Baja are in the late stages of pregnancy, the other half are going there to mate. The females are promiscuous and will mate with more than one partner. Grays can mate one on one, or sometimes they mate in groups of 10 or more. If you can imagine the thrashing of beasts this size you will understand why no one has gotten close enough to study it in detail.
The whales rest in and near the lagoons of Baja California for a month, new mothers for about 3 months. So why migrate? First, the water temps in the Arctic are near freezing, compared to about 20degrees in the lagoons. Their body temp is 38degrees (37degrees for humans). The newborn calves need the warmth because their blubber and fat stores are not fully developed. Second, as the arctic sun sets in the winter, so does the food supply. Even with blubber, it costs a lot of energy for a mammal to maintain body temperature in those waters. A whale actually expends less energy swimming slowly south and back than it would if it stayed in the icy Bering Sea. Grays are neutrally buoyant and can just hang in the lagoons with little effort.
Mother & Calf
After a pregnancy of 13 months, the newborn gray whale calf is 4.7m long and weighs 1100kg. They are completely dependent on their moms. For the first several weeks the pair stays in the inner lagoon. As the calf gets more comfortable swimming it will spy hop and breach, and the pair will move nearer to the lagoon entrance and make forays outside the lagoon. Mother and calf pairs will also congregate, perhaps like human mothers taking their kids to the park for a playdate, much to the delight of whale watchers lucky enough to witness this from a boat. Grays have become famous for friendly interactions with humans, especially in the lagoons. To nurse, the calf does not suck, instead the mother squirts the incredibly fat-rich milk from a teat into the calves mouth. The calf will triple its weight to about 3300kg during its 2 month stay. That is a gain of 1.5kg per hour.
The grays head back north in 2 separate pulses. The males and newly impregnated females leave first, around mid-February (in fact, some of the whales start the return trip back before they even reach Baja). New moms need to wait until the calf is fit enough to make the journey, somewhere around mid-April. It has now been 6 months since the mother has eaten, and it will still be nursing its calf, all while swimming another 10,000km north. Females are larger than males because of the extra fat reserves they need for this incredible feat.
Orcas are beautiful creatures in their own right, but Bigg’s killer whales are amongst the only natural predators of gray whales. They are pack hunters that attack the vulnerable calves, especially near Monterey, CA were the shallow waters of the offshore continental shelf give way to deep submarine canyons. The killers bite the calf or give it body slams, but mostly they try to drown the calf by riding up on it. In defense, the mother will try to move to shallow water or swim underneath its baby and support it out of the killer’s reach. Mortality from killer whales can be as high as 35% of the calves.
This is the last leg of the 20,000km adventure, the longest migration of any mammalian population. Unimak Pass is the first gap between the Alaskan peninsula and the chain of Aleutian Islands, making it the gateway to the Bering Sea. It is a pinch point through which all of the grays will pass, and another place on the route where Bigg’s killer whales lie in waiting. It is a time of danger, but also of great anticipation.
The whaling industry completely wiped out gray whales from the Atlantic Ocean by the late 1700s. When whaling began along the west coast of North America in the 1800s, the population is believed to have been around 25,000. By 1900 there might have been as few as 800 surviving. Grays were given international protection in 1946. Their numbers increased to 11,000 by 1967, 17,000 by 1980 and 20,000 by 2000. A rare success story, in 1994 the gray whale population of the Eastern Pacific Ocean was delisted as an endangered species.
Breaching is one of those great spectacles of nature when a whale jumps out of water and lands on its side with a great splash. It is mostly youngsters that engage in this activity. They do it just for fun!
Song of the Gray Whale
Grays don’t “sing” in the way we typically think of whale songs.Their vocalizations are mostly pops, clicks, grunts and moans. Gray whales share a common ancestor with hippos. 54 million years ago this 4 legged terrestrial mammal about the size of a kitty cat dipped its toes in the ocean and eventually decided to stay. To this day, rising above the din of millennia, epochs, even whole geologic eras of evolution, you can hear the song of the gray whale.