The giants of the sea
The biggest animals to have ever lived on our planet, blue whales are a charismatic species found across the world’s oceans.
Ranging in size from 79 ft in the Indian Ocean’s pygmy blue whale subspecies to more than 100 ft in Antarctic blue whales, these marine mammals were once hunted to near extinction.
In order to reconstruct past level of whales and discover if blue whale populations were recovering or not after the banning of commercial whaling in the 1980s, scientists have developed models that explain both old whaling catch records and modern-day counts.
Whaling records were incredibly detailed, recording data on every whale caught: species, size, sex, weight, fetus information, who caught them, the nationality of the boat, and date.
These historical datasets were used in decision-making by the International Whaling Commission to realize the Antarctic blue whale was almost extinct and to put a full moratorium on commercial whaling of the species in the 1960s.
Today, researchers like Professor Trevor Branch at UW are using statistical methods and models to study different whale populations across the globe and judge recovery levels.
He has been doing this work for decades. Fitting a model to data sets, he reconstructed what levels of whales there were, are now, and will be in the future, and judging whether they are in recovery or not.
There are many success stories. Almost every large whale population is recovering because whaling was the single biggest impact on these marine mammals in the past. Humpbacks are doing very well, and the blue whales on the Pacific Coast of the US have numbers suggesting they are fully recovered. Others like Antarctic blue whales are recovering but at very low levels, perhaps only 1% of pre-whaling levels.
Not all large whale populations are in good shape, however. North Atlantic right whales are still dying from entanglement with fishing gear and ship strikes, causing a decline in their numbers and raising the risk of extinction given their small population size.
Branch says it’s important to highlight the success stories in conservation of large whale species. Putting research intro practice, sharing why and how it helped recovery, and using it for other populations is vital.
His current work is focused on the assessment of pygmy blue whale populations in the Indian Ocean, with every population having a unique song. The whales repeat these songs over and over, and they are thought to have a mating function since only males sing them. These distinct calls stay stable over many decades, and he is using this information to figure out where each population resides, and therefore how many were caught from each during the whaling era. This will help him to assess trends in number over time for each of these populations… all based on their song!
On World Whale Day, we’re recognizing the importance of whales to the planet’s ecosystems and celebrating the recovery levels seen in most species whilst continuing to conduct research to tackle the continued negative impacts on the few that are still in danger due to human actions.