When the world came together to agree on a global ban on the hunting of blue whales, it was the first time nations had ever collectively decided to save a species from extinction. But three decades on, and it appears that the giant marine mammals in the southern hemisphere are a lot slower at recovering than previously thought, and that climate change may make this even slower.
Looking back at records on five species of baleen whales that live in the Antarctic waters dating from 1890 to the present day, researchers have been able to assess how well they have been recovering since the whaling ban came into place in the 1980s, and how future alterations due to climate change may impact them. And for some whales, the outlook is not great.
Publishing their results in the Fish and Fisheries journal next month, the scientists found that by 2100, blue, fin, and southern right whales are not even expected to reach half the pre-whaling population sizes they once experienced. Their slow reproduction rate, coupled with the impact that climate change is expected to have on their food, means that the cetaceans will struggle to up their numbers.
The study has looked in unprecedented detail at how the populations of blue, fin, minke, humpback, and southern right whales have responded to the differing pressures over the 127 years that current records cover, and how they may fair in the future, using the newly developed Model of Intermediate Complexity for Ecosystem Assessments (MICE).
“Our MICE model uses whale numbers dating back from 1890 to now and then couples this with food availability and ocean physics to understand the changes to ocean conditions that whales are likely to experience,” explained Dr Eva Plaganyi, from the Commonwealth Scientific and Industrial Research Organisation (CSIRO).
The results go to show how the legacy of commercial whaling, in which blue whales were hunted mercilessly for their meat and oil until just 400 remained, is still impacting the animals today, and will continue to do so long into the future.
The main issue here is their achingly slow reproductive time. For example, southern right, whales which were reduced to just 300 individuals, only have one calf every two to three years. Contrast this with the humpback whales, who pop one out every year, and it is easy to see why the latter is faring so much better, and expected to make a full recovery by 2050. The same is true of minke whales, although the population in the southern hemisphere is still having to deal with hunting, as Japan continues to target them.
The researchers hope that their new data can inform better conservation and management plans for cetaceans in Antarctica.