Project Manaia

Fin Whales: Social Cetaceans of the Sea

Sometimes coming in second can feel like missing out, but for the fin whale (Balaenoptera physalus) being the second largest mammal on earth is an impressive place to be. Weighing in at 120,000 kg, and reaching up to 27 meters in length, the fin whale is an elegant second in size to its cousin, the blue whale. And the fin whale comes in first for speed within the whale family: swimming up to 47 km/hour.

Fin whales have many intriguing physical features, including a prominent dorsal fin and a distinct ridge that runs from the dorsal fin to the tail. Unique V-shaped patterns behind their heads can identify individuals since they differ on each whale. Fin whales also have a puzzling mismatch on the lower jaw. The right lower jaw is a solid dark gray, while the left is a mottled variation of white and gray. Though many theories have been suggested for this uneven coloration, none have been proven, and the purpose, or perhaps lack of purpose, remains unclear.

Fin Whale Populations

There are two subspecies of fin whale, the northern fin whale which lives in the north Atlantic and the southern fin whale which lives in the Southern Ocean. Fin whales found in the Mediterranean fall into two categories: visitors from the north Atlantic and a resident population. The resident population does not qualify for species status, but it does have clear physical and behavioral traits and even specific genetic markers. Physically, the resident whales only appear to differ from the north Atlantic population in that they are slightly smaller. Behaviorally, however, there are several distinctions.

Unique Mediterranean Fin Whales

Fin whale calves are usually born in the fall, but in the Mediterranean, there are calves born all year long—though births do peak in the fall. It is likely that this breeding flexibility has to do with consistent food sources in the Mediterranean Sea. In fact, many fin whales outside the Mediterranean fast during the winter while migrating to warmer waters. The resident Mediterranean population tends to migrate less and can find food more easily throughout the year.

This unusual situation for the resident Mediterranean fin whales also leads to another interesting contrast to their north Atlantic counterparts. Fin whales and blue whales have the lowest frequency vocalizations of any species on earth. They primarily use these sounds to communicate during breeding season, but in the Mediterranean, fin whales vocalize all year long. Research indicates that this is a result of both the expanded breeding season and the relatively small size of the Mediterranean Sea which allows for easier communication.

Baleen Whales

Fin whales are baleen whales, a group that includes four families and 16 species: the right and bowhead whales (family Balaenidae), gray whales (Eschrichtiidae), pygmy right whales (Cetotheriidae) and the fin whale’s family, Balaenopteridae, which contains 10 species. Whales in Balaenopteridae range from the “smallest” member, the northern minke whale which reaches 9 tonnes, to the largest member, the blue whale. Baleen whales split from the toothed whales (Odontoceti) around 34 million years ago. There are many more toothed whales, 73, including the sperm and beaked whales.

Baleen whales filter their food out of giant mouthfuls of water. Fin whales can take in an incredible 70 cubic meters of water filled with lots of their favorite foods: small fish, squid, copepods and krill. They then expel the water from their mouths while trapping prey inside with the filter-like baleen bristles. Each gulp provides the fin whale with approximately 10 kg of food.

Mediterranean Fin Whale Locations

Fin whales are most common in the central and western parts of the Mediterranean, mainly north and east of the Balearic Islands. They concentrate in the Ligurian Sea and the Gulf of Lyon in summer but expand to cover much of the western and central Mediterranean in winter. They are rare in the southern and eastern Mediterranean and have not been found in the Adriatic or Aegean Seas or the Black Sea.   

Threats to Fin Whales

Unfortunately, some of the most popular fin whale feeding locations correspond to high concentrations of microplastics. This is likely due to areas of high trophic upwellings, which tend to bring up both microplastics and the nutrient rich foods the whales crave.

Other threats include a potential reduction in food due to warming seas and climate change and mortalities due to ship strikes. Ship strikes are especially common in the Mediterranean and are the main cause of human-induced mortalities here. In one particularly troubling case, a distressed fin whale calf repeatedly rammed its head into seawalls in Sorrento Harbor off the coast of Italy. When divers followed the calf back out to sea, they found the calf’s mother, dead from a ship strike. The Italian Coast Guard responded but the calf swam away before help could be provided.

Like other whales, fin whales were hunted nearly to extinction in the 20th century. Hunting restrictions and international protections have helped to bring them back from the brink. The IUCN lists them as vulnerable internationally, with the Mediterranean population listed as endangered, with only around 2,500 individuals. Within the Mediterranean fin whales are protected by several laws including the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS).

A Social Cetacean

Perhaps the most compelling fin whale quality is their sociability. They are often found in pairs or small groups, and sometimes gather in the hundreds. There may be many reasons for their sociable behavior, but one appears to be a benefit to feeding. Fin whales will sometimes work together, swimming in circles around their prey, frightening them into a tight ball, making it easier to eat a large amount of food all at once.

And fin whales don’t just congregate with their own species, they have been known to feed in large groups that include humpback and minke whales and Atlantic white-sided dolphins. In fact, fin whales are so friendly with the biggest mammal on earth, the blue whale, that the two sometimes mate and produce hybrids.

Written by Rachel Endicott

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