A Dalliance With Dolphins
The researchers aboard the NOAA vessel R/V Fulmar, a sturdy 67 ft. catamaran, were following a predetermined east-west line transect 30 miles off the Marin coast. The scientists scanned primarily for marine mammals and seabirds, key indicators of the ocean’s health. They stopped occasionally to deploy nets and instruments to sample for invertebrates, chemistry and water conditions. Thus far, they’d logged several species of gulls, terns, shearwaters, murres, and fulmars (the vessel’s feathery namesakes). Several humpback whales were seen feeding on subsurface swarms of tiny shrimplike krill that showed on the captain’s “fishfinder” sonar. They’d also encountered a northern fur seal resting at the surface, it’s long, leathery foreflipper arched over its body in a “basket handle” position.
Squinting into the distance, the captain saw a commotion in the skies ahead, then a commotion on the water: over a hundred gulls and terns were hovering and diving repeatedly in dizzying aerial zigzags. Closing in, he saw one or two dark forms leaping vertically in acrobatic pirouettes. The reason soon became evident: the waters were a-boil with dolphins - nearly a hundred - corralling, confusing and feasting on a school of anchovies, with swift swoops, somersaults and dives. Handsome black-and-white bodies sliced through the shoal of fish, tracing crazy-quilt patterns in the foaming, churning blue-green ocean. Several swung away to visit the boat and look up at those on board: some looking back, but others furiously entering data on numbers, behaviors, presence of cow-calf pairs, and notes on probable prey. Who was having more fun?
These were Pacifiic white-sided dolphins (Lagenorhynchus obliquidens), an open-ocean offshore species ranging from California across the north Pacific to waters off China and southern Japan. Of the many dolphin and porpoise species in the sanctuary, these “lags” are frequently seen.
Like most dolphins, they are admirably designed for speed, an asset when prey is swift or scattered. Their streamlined bodies and powerful tail flukes help them achieve prodigious speeds, over 25mph in bursts. They’re gregarious, living in herds numbering into the thousands but are more commonly seen in groups between 10 and 100. Off Washington, Oregon, and California there are over 21,000 of them. Feeding on schooling fish and squid, they’re nomadic, and forage over a large area. When seeking prey, “outriders” may scatter to scout for dense patches of food; it’s surmised that the dolphins’ aerial leaps may be how they spot prey at a distance, looking for telltale flocks of wheeling, circling seabirds in the air indicating the presence of fish below. And probably these outriders then signal to the herd, “Jackpot!”
“Lags” have distinctive white ‘paneling’ on their sides, and a prominent hooked dorsal fin. At between 5.5 and 8 feet long, they weigh a robust 300 to 400 lbs. Pacific white-sided dolphins may live over 40 years. Newborn calves weigh about 30 pounds, and are about 3 to 4 feet long. Mothers nurse their calves for up to 18 months.
Though not endangered, Pacific white-sided dolphins in the U.S. are protected under the Marine Mammal Protection Act. A primary threat is entanglement in fishing gear, such as gillnets and trawls. Also, like all dolphins, these are highly acoustic animals, relying on vocalizations to locate prey, mates, and maintain social and familial cohesiveness with their clicks and whistles, and churrs, so anthropogenic (human caused) ocean noise poses a significant additional threat.
NOAA’s Greater Farallones National Marine Sanctuary uses research to inform management of our wildlife resources, and shares data with other conservation agencies and researchers. The sanctuary offers monthly Sanctuary Explorations to experience different marine life and habitats, including Farallones Nature cruises, usually in the fall. To learn more, see https://farallones.noaa.gov/visit/exploration-program.html.
