It seems social distancing rules don’t apply to blue whales! Almost 50 of the ginormous animals have been spotted recently gathered around the Farallon Islands in what may be the highest concentration of large marine mammals documented in Northern California waters in 20 years. But why is this such a big deal?

Blue whales can weigh as much as 200 tons (181 metric tonnes), and can reach up to about 110 feet (34 metres) in length. Image © NOAA

The Farallon Islands, off the coast of San Francisco, are one of the world’s great biodiversity hotspots. While scientists regularly visit the area to study sharks or birds, the current focus has been on the 47 blue whales recently documented around the Farallones. The blue whale (Balaenoptera musculus) belongs to the baleen whale suborder Mysticeti and is the largest animal on the planet. Weighing as much as 200 tons (181 metric tonnes), they can reach up to about 110 feet (34 metres) in length and their mottled blue-grey colour can be used to identify individuals. The giant animals are listed as endangered under the Endangered Species Act.

The recently sighted blue whales not only left visible "footprints" — smooth patches on the ocean’s surface formed when whales dive and push water up with their flukes — but they also announced their presence with spray from their blowholes. Blue whales feed almost exclusively on krill, straining huge volumes of water through their baleen plates to sieve out up to six tons of the shrimp-like crustaceans in a single day. Krill are found in all the world’s oceans and make up an important component of many ecosystems. The name comes from the Norwegian word krill, meaning "small fry of fish" also known as "whale food," since they form a large portion of many whales’ diets. 

The waters around the Farallon Islands, off the coast of San Francisco, are rich in biodiversity. Image © Jan Roletto

"It’s extraordinary. It may be an absolute record," NOAA Greater Farallones spokeswoman, Mary Jane Schramm told Marine Industry News. "Essentially, the driver here is krill and that’s the food they [the whales] feed upon this time of year, and we have it in such great abundance in the marine sanctuary that the blue whales have apparently targeted our water specifically to feed."

But their need to feed may be putting them in harm’s way. "Their enormous size dictates that they maximise feeding effort when food is available, and this sometimes takes them into dangerous waters," explains Maria Brown, superintendent of the Greater Farallones National Marine Sanctuary in a press statement. "While focused on feeding, they are not likely to recognise or evade a ship’s approach."

The biggest threats currently facing blue whales are vessel strikes and getting entangled in fishing gear. Due to this, many officials and conservationists have called for large ships to slow down while sailing near the whales' feeding grounds. The Coast Guard along with the National Oceanic and Atmospheric Administration (NOAA) – the organisation that manages the marine sanctuary that surrounds the Farallones – have requested that large vessels slow down to 10 knots when sailing through the area. "The sanctuaries are working with the U.S. Coast Guard to notify mariners to be on the lookout for the whales and maintain slow speed and maximum possible distance to avoid deadly collisions," says Brown.

The biggest threats currently facing blue whales are vessel strikes and getting entangled in fishing gear. Image © John Calambokidis, Cascadia Research Collective

The blue whales have been around for a few days, with scientists on the island counting 23 of the animals in the area a few days before the number jumped up to 47. Nobody can predict how long this group of blue whales will stay in the area for, but here’s hoping they take advantage of the aquatic smorgasbord and quieter waters as a result of COVID-19.

Top header image: Michael Bamford, Flickr