Science

Is It a Whale? A Dolphin? Or a Shark?

SD 1023 captured this image in the Arctic, sparking a lively discussion among the Saildrone team and our science partners.

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Saildrone
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April 10, 2019

The sky, sea, and horizon cameras mounted on Saildrone unmanned surface vehicles (USVs) capture many spectacular sunsets and sunrises and some pretty impressive shots of ocean storms. But the cameras don’t shoot continuously, and given how vast the ocean is, it’s a pretty rare occasion to catch an example of wandering wildlife up close.

So, we were really excited to discover this image captured by SD 1023 during the 2018 mission to the Chukchi Sea to measure CO2 and the abundance of Arctic cod, and it sparked a lively discussion amongst the team here at Saildrone HQ trying to “name that fin.” Jaws was suggested at least once.

Saildrone Arctic mission fin whale surfacing
What type of fish or marine mammal do you think this breaching fin belongs to?

Our friends over at NOAA’s Pacific Marine Environmental Laboratory (PMEL) were excited about the image, too. We’ve completed several missions in the Arctic with PMEL, including two missions that used a passive acoustic sensor from Acousonde to listen for North Pacific right whales, but until this photograph, we had never seen a whale surfacing in that region.

NOAA/PMEL scientists deduced that this image is most likely a species of baleen whale. Baleen whales have plates along their upper jaws to filter food from the water and generally prefer the colder waters of the Arctic and Antarctic. They noted the slender, streamlined shape of the body, characteristic of rorqual (minke, sei, fin, and blue) whales and the pointy dorsal fin.

“If we had to get really specific, we think it is a juvenile fin whale,” concluded the team on the PMEL mission blog. “The white bubble you see is most likely from wash as the fluke (tail) of the whale pulls down as the whale dives.”

The fin whale, which takes its name from the fin on its back, is the second largest species of whale after the blue whale—they can grow up to 26 meters (85 feet) long. They live primarily in deep, offshore waters at temperate to polar latitudes, and have a lifespan of up to 90 years. Many individuals can be identified by unique markings behind their heads and on the underside of their tail flukes.

NOAA Fin whale
The fin whale Balaenoptera physalus is the second largest baleen whale species after the blue whale. Illustration: NOAA.

Fin whales are listed as an endangered species. Commercial whaling took hundreds of thousands of individuals in the early part of the 19th century, some 725,000 in the Southern Hemisphere alone. Today the fin whale’s major threats are vessel strikes, a lack of food due to overfishing (krill is an important source of nourishment), entanglement in fishing gear, and ocean noise. Stock assessments suggest that there are only about 100,000 left in the world’s oceans.

Saildrone USVs are wind and solar-powered ocean drones that carry a suite of science sensors to capture critical oceanographic and meteorological data above and below the sea surface, including acoustic sensors for fishery surveys and animal tracking. Being 100% powered by renewable energy and completely silent, they are an ideal platform to study the ocean environment without disturbing local wildlife.

Saildrones have been proven to be effective tools to augment ship-based surveys tracking great white sharks in the Pacific and northern fur seals in the Arctic, studying natural oil seeps in the Gulf of Mexico, and quantifying air-sea carbon exchange in the Atlantic, among others.