Has the hunting of whales to the brink of extinction in the twentieth century caused a drop in krill numbers in the Southern Ocean? With almost two million whales killed in the Southern Ocean between 1900 and 1970 you would think that the krill would be pretty happy. Thriving with one of their major predators missing from the food chain.
There is one scientist from Tasmania’s school of Zoology who thinks the large drop in whale numbers may have led to krill changing their behaviour for the worse. Because they are not being hunted so much they may be reproducing more slowly and in fewer numbers. These changes are causing krill populations to drop off.
This scientist is Jay Willis. He has tracked the life of krill.
This idea of less whales equals less krill reverses the predictions of increases in krill numbers with the drop of almost two million in the whale population. Krill populations are tricky to measure and there may be a long term decline that has nothing to do with whales. This would make Jay’s theory less important.
So if it’s not whales or other predators that are reducing krill numbers what is?
Warming in the Southern Ocean means less sea-ice. Krill use sea ice for protection, a place to lay their eggs and a place to find food that grows on the underside of the ice. Less sea-ice makes it harder for krill to survive.
Another challenge for krill is that the Southern Ocean is absorbing more and more carbon dioxide (CO2) from the air. This extra CO2 is created when we burn fossil fuels like oil, gas and coal to create energy. Almost one third of all CO2 is absorbed by our oceans. This makes our oceans more acidic every year.
When the CO2 mixes with sea water in the Southern Ocean the water becomes more acidic. This increase in acidity of the ocean means it’s more difficult for krill to make their shell and more difficult to survive.