Where do tohorā – southern right whales feed?
Recovery in tohorā – southern right whales is linked to environmental conditions and food abundance in areas thought to be important feeding grounds. This is probably because tohorā – southern right whale mums need to eat a lot to get in good enough condition to have a baby. Mums will have one baby, on average, every three years, and she will loose about 25% of her body weight while nursing her baby in the first few months of its life. If mum doesn’t have enough food, she’s not fat enough to do this. However, while we know that southern right whales feed on copepods and krill, wee marine crustaceans, we don’t have a good idea about where the most important feeding grounds are, particularly around Aotearoa New Zealand and Australia.
Uncovering foraging grounds for conservation
How can we protect tohorā – southern right whales if we don’t know where they are 9 months of the year? Researchers from the University of Auckland and Cawthron Institute are using satellite tracking technology and micro chemical markers to understand where and on what tohorā – southern right whales feed. Knowing where the whales are going, and how they get there, will allow us to understand how their movements interact with shipping lanes, coastal development and oil and gas exploration. Climate change will also impact different areas of the Southern Ocean differently: if we know where the whales are feeding, we can understand how their future recovery might be influenced by the changing seas.
You are what you eat
Microchemical markers called stable isotopes vary predictably across the Southern Ocean, like a map. The same microchemical markers found in the whale’s skin tell us where on the map the whale has been feeding in the past few months before we see it on the wintering grounds. Using remote biopsy systems, we take small skin biopsy samples, about the size of your fingernail, from the whales and use it to understand where the whales were during the summer months.
By attaching satellite tags to the tohorā – southern right whales, we can follow the whales on their voyage from the Auckland Islands to their offshore foraging grounds. These tags give day-by-day tracks of the whale’s movements, providing not just where the whales are eating, but how they are getting there, if they cross shipping lanes or oil or gas fields. This will provide important information for how we manage our oceans.
So far – surprises!
Six tohorā – southern right whales were tagged in 2020 and the tracked whales went southwest. Tahi and Bill went about 5000 km west of the Auckland Islands, half way to South Africa! This was a surprise because the historical whaling data shows southern right whales were killed northeast of Aotearoa New Zealand – an area none of our whales visited. Perhaps the whales tagged in 2021 will head there?