Fin whales are the second-largest in the world, growing up to 85 feet (26 m) long and 160,000 pounds (72.3 metric tons). In 1976, the numbers of these magnificent giants in the Antarctic were dangerously low, caused by human commercial hunting practices. This caused a ban on commercial whaling to be put into place and thankfully the species bounced back: another conservational triumph!

How can you track whale populations?

Careful monitoring from researchers and filmmakers revealed large groups of up to 150 southern fin whales in their historical feeding areas, this is the highest number on record using modern methods. “I’d never seen so many whales in one place before and was absolutely fascinated watching these massive groups feed,” exclaimed Professor Bettina Meyer, from the University of Hamburg, who worked on the project.

Using a helicopter to survey the area, the research group covered a total of 3251 kilometers and counted 100 groups of fin whales. A team from the boat deck also spotted a group of 50 giants near Elephant Island and later more than 70 in the same location.

The relationship between krill and fin whales

The overall aim of the project was actually to evaluate the impact of climate change on Antarctic krill populations in the area. As this species is the foundation of the Antarctic food chain – being the prime food source for fish, seals, penguins, and whales – their activity can tell us a lot about the rest of the ecosystem.

The krill and fin whale populations have a delicate and codependent relationship for them to flourish. As the number of whales grows through feeding on krill, their excrement increases the amount of nutrients – such as iron – in the ocean. This acts as fertilizer for phytoplankton (microalgae), which are krill’s main food source, and allows their numbers to flourish.

“When the whale population grows, the animals recycle more nutrients, increasing the productivity of the Southern Ocean. This boosts the growth of algae, which for their part absorb carbon dioxide from the atmosphere through photosynthesis, reducing the atmospheric CO2 concentration,” explains Meyer.

The return of these fin whales to the region is not only great news for krill populations, but also for the rebound of all the species that rely on the crustaceans as a food source.

Source study: Scientific Reports – Return of large fin whale feeding aggregations to historical whaling grounds in the Southern Ocean