Blue whales believed to be foraging in South Taranaki Bight
Science Centres: Coasts and Oceans
A recent study indicates that blue whales in the South Taranaki Bight might be doing more than just passing through on their way to and from summer feeding grounds in Antarctica.
Carried out by the National Institute for Water and Atmospheric Research (NIWA), the study examined opportunistic sightings of blue whales collected between 1979 and 1999, historical whaling data, stranding events, foraging observations, and sightings recorded during two seismic surveys conducted in 2011.
The findings show that the presence of blue whales in the South Taranaki Bight is greater than expected and historical whaling data demonstrate a high density of blue whales in the region throughout time.
The study links this increased presence of blue whales in the Bight to the prominent upwelling system near the South Island's Farewell Spit that generates large clouds of plankton – perfect blue whale food - in the South Taranaki Bight.
Despite being more than 20 metres in length and weighing more than 100 tonnes, the blue whale remains one of the world's most elusive creatures. Southern Hemisphere blue whales were intensively hunted during the whaling era, leaving only small populations behind. Sightings are rare and little is known about the distribution patterns of blue whales, the world's largest animal.
NIWA marine ecologist Dr Leigh Torres said that the study would significantly enhance people's understanding of the distribution and foraging grounds of blue whales in the Southern Hemisphere.
"Conventional wisdom has been that blue whales only transit through New Zealand waters while migrating. But this new information suggests that this is not an accurate understanding of their ecology. Blue whales appear to be present in the South Taranaki Bight with some regularity and density, and based on their foraging patterns and the availability of their prey in the area, we think they are feeding here."
"Blue whales are huge and need to eat vast amounts of food, which are tiny plankton, to support their energy demands. But there are just four confirmed blue whale foraging grounds in the Southern Hemisphere outside of Antarctic waters. So, it's very important that we properly document and protect their foraging grounds."
Currently, the blue whale is classified as a "migrant" under the New Zealand Threat Classification System, which means they aren't afforded the same level of conservation protections as other large baleen whales that use coastal waters around New Zealand such as the southern right whale.
Dr Torres said that, although further work was necessary to determine the scale and significance of the foraging ground in the South Taranaki Bight, the new information may prompt a rethink on how blue whales are classified in New Zealand.
"The South Taranaki Bight is also the largest offshore natural gas and oil exploration area in New Zealand, with seven production platforms, considerable seafloor pipelines, and significant plans for expansion in the near future. Shipping traffic and seabed mining activities have been shown to impact blue whales directly – altering their behaviour and degrading their habitat through acoustic disturbance and ship strikes. We need to gain a better understanding of how and when blue whales forage here so that possible impacts can be avoided."
This research was done with the support of the oil and gas industry, which provided information about sightings of blue whales in the area. The study was funded by OMV NZ Limited and NIWA, and has just been published in the New Zealand Journal of Marine and Freshwater Research.
Since the study was accepted for publication, 49 additional blue whale sightings in the South Taranaki Bight have been reported to Dr Torres, including 33 sightings by marine mammal observers during a recent seismic survey earlier this year.
For comment, contact:
Dr Leigh Torres
Marine Ecologist, NIWA
Tel: 04 382 1628
The full study and results, Evidence for an unrecognised blue whale foraging ground in New Zealand, are available online.
Research for this report included analysis of a database curated by the Department of Conservation where each sighting is validated, sightings recorded by trained observers onboard ships collected between 1979 and 1999, sightings recorded by scientists and vessel captains at NIWA and photo verified, foraging observations, stranding records, historical whaling records, as well as sightings recorded during two seismic surveys conducted in 2011. The study includes both blue whale subspecies because it is difficult to distinguish between an Antarctic and pygmy blue whale without genetic analysis.
Blue whales (Balaenoptera musculus) were exploited by whaling operations in the 20th century, reducing the Antarctic blue whale population to less than 1 per cent of its original population. In the Southern Hemisphere, two subspecies of blue whales are recognised – the Antarctic (or true) blue whale and the pygmy blue whale.Only four blue whale foraging grounds have been documented in the Southern Hemisphere outside Antarctic waters – the south western coasts of Australia, near the fjords of southern Chile, near the Crozet Islands in the Indian Ocean and on the Madagascar Plateau.