Southern Right Whales
Southern Right Whales - Tohora - Eubalaena Australis
The Whale's Story: Southern right whales used to be very common in New Zealand's coastal waters. The early settlers of Wellington apparently complained of being kept awake at night by the noise of the whales in the harbour. With the arrival of commercial whaling in the 19th century, right whale numbers plummeted because they were the "right" whale to hunt. By the start of the 20th century right whale sightings were very rare in New Zealand, and it was feared they had been hunted to extinction. That was until the 1980s when stories emerged of a population of whales clinging on in the remote sub-Antarctic Auckland Islands. Since then, researchers have been visiting the Auckland Islands during the whales' winter breeding season to learn more about these gentle giants.
For most of the year, right whales are roaming the southern ocean looking for dense concentrations of their zooplankton food, principally copepods and krill. The prime foraging areas are probably where plankton is aggregated in regions of high productivity, such as the sub-tropical convergence around 500 to 1000 km south of Australia. This is a region where warm, salty sub-tropical water from the north meets cold, nutrient rich sub-Antarctic water from the south which causes this high productivity. After fattening up in the wild southern ocean, southern right whales look for sheltered locations in winter for mating and calving. The Auckland Islands provide just such a habitat. Port Ross is a large, shallow harbour at the northern end of the islands. It is sheltered from the prevailing westerly winds and swells and is a real hotspot for right whales. Mature females seek out these calm waters to give birth and nurse their calves, while males and juveniles seem to view Port Ross as a lively hang-out where they can socialise with other whales. Right whales don't reach sexual maturity until about 9 years old, but that doesn't stop the juveniles practising their mating behaviour! Mating is often a very vigorous affair. Several males will pursue one female, jostling for the prime position to copulate with her. Fertilisation is probably achieved by the last male to mate with the female or by the one who produces the most sperm - right whales have the largest testes in the animal kingdom! The gestation period is 12-13 months, and after being born the calf stays with its mother for about a year. The period of nursing is relatively short, thanks to the very high fat content of the milk, which allows the right whale calf to grow very rapidly.
Port Ross is only about 13 km long, but might contain more than 100 right whales on a good day. We make use of these high densities to study aspects of the species' ecology essential for understanding how right whales are bouncing back since whaling ceased. Each whale has a unique pattern of callosities on its head (the callosities are actually patches of rough skin, infested by whale lice called cyamids). These patterns allow us to recognise individuals and build up a sighting history through time. Analyses of these sighting histories can tell us about population size, reproductive and survival rates and movements of individuals. We also use our sighting data to learn about the whales' preferred habitats. In the calving season, nursing mothers have a strong preference for inshore waters, sheltered from wind and swell - probably to reduce energy expenditure by their calves. Other right whales are less vulnerable, and therefore less choosy, making use of more exposed areas further from the coast.
Mother and calf at Port Ross. Photo: Will Rayment.
As the early settlers in Wellington would attest, southern right whales are a noisy bunch. We have been using our visits to the Auckland Islands to learn about the sounds they make and why they make them. Elsewhere in the world, other right whale species have been shown to modify their acoustic behaviour in response to noise pollution in the ocean. With little to no human activity around the Auckland Islands the acoustic environment is about as pristine as it could be. It's a different story around the New Zealand coast though, so understanding the whales' reaction to noise pollution is essential.
Southern rights are genetically differentiated based on philopatry to their calving grounds (Australia, NZ, South Africa, Argentina) but are still considered the same species. There is a possibility of gene flow, either through mixing on feeding grounds, or females occasionally calving in different locations. This is possible as there are no big land masses in the Southern Ocean. Right whales don't cross the equator, so southern rights are isolated from the two northern species (North Atlantic and North Pacific right whales), which in turn are separated by the northern hemisphere landmasses. Australian and NZ right whales are considered the same species, but different enough to be different stocks (based on mitochondrial DNA) but there must be some genetic exchange (based on nuclear DNA). Indeed, photo-ID matches have shown that the same female has had calves on both sides of the Tasman.
Whale at Port Ross. Photo: Will Rayment.
The Scientist: Dr Will Rayment - University of Otago.
I made my first trip to the Auckland Islands in 2008, aboard the expedition yacht Evohe. I instantly fell in love with the wild, untamed nature of the location, and the sheer abundance and exuberance of the wildlife. I have been back every year since then, most recently leading a research team aboard the University of Otago's vessel Polaris II. We head down in July and August each year because this is the peak of the right whale breeding season. While we are carrying out our research on right whales in the Auckland Islands we use Polaris II as our floating base. Every morning we use Polaris' crane to launch our small boats, and then head off in search of whales. We systematically search the area, carefully recording our survey effort and the locations of whale sightings. At each sighting we record details of the habitat and try to obtain photo-IDs. It's mostly really fun, especially when we have close encounters with curious whales, but can be very challenging if the weather is bad. After a long day in the wind, rain and snow it's awesome to be able to return to Polaris for a warm meal and a hot shower.
Studying southern right whales in the Auckland Islands is a real
privilege and great fun. Everything we learn can be applied to help understand
how the population is recovering and make predictions about recolonisation of
former habitats around the New Zealand mainland. It's exciting to think that
one day, places such as Otago and Wellington Harbours might be chock full of
right whales again.
Useful Links: http://www.otago.ac.nz/marinescience/staff/willray...