First non-lethal whale study answers big questions
Between February and March this year, the six week Australia-New Zealand-led expedition used skin biopsy, photography, satellite tagging, and passive and active acoustics to study the population structure, distribution, movement, feeding and ecological role of Southern Ocean whales. The expedition was the first project conducted under the banner of the Southern Ocean Research Partnership (SORP), which was formed in March 2009 and involves 12 countries.
'The partnership aims to provide the results of non-lethal research to the International Whaling Commission as a scientific basis for sound conservation and management of Southern Ocean whales,' says expedition leader Dr Nick Gales, of the Australian Antarctic Division.Working from two small boats (supported by New Zealand's research vessel, Tangaroa) the research team collected 64 skin biopsy samples and 61 individual tail fluke photographs from humpback whales. They also satellite tagged 30 humpback whales in their Southern Ocean feeding grounds. By deploying 110 sonobuoys (passive 'listening' devices), they recorded sounds from blue, humpback, minke, fin and sperm whales and an unidentified beaked whale and tracked the movements of blue whales for 36 hours.
'This is the first time small boats have been used to work with whales on the high seas in the challenging Antarctic environment, but they proved highly successful, despite the generally poor weather experienced during the trip,' Dr Gales says.
Individual or pods of whales were sighted 326 times, accounting for at least 624 animals from eight species. Blue whales proved elusive, however, despite acoustic detection of their presence. Humpback whales were the most commonly sighted species, particularly around the Balleny Islands.
'On occasions when whales were sighted in good weather, the small boats were launched,' Dr Gales says.
'The sightings surveys will contribute to one of the major SORP projects investigating the distribution and mixing of Southern Hemisphere humpback whale populations around Antarctica.'The satellite tagging results will also feed into this project by providing information on the medium-scale movement of humpbacks in their Antarctic feeding grounds, and links between their Antarctic feeding grounds and their tropical breeding grounds. While the team tagged 30 humpback whales, the failure of a newly designed tag meant that fewer tags than expected succeeded in transmitting daily whale locations. These should continue to transmit for at least several months.
'The working tags will provide valuable data on the foraging behaviour of these animals, and we hope to be able to establish migratory routes between the Balleny Islands region and the tropical humpback whale breeding grounds,' Dr Gales says.
Photo-identification will also help build the distribution and mixing picture.
'Matching tail fluke photos taken in the feeding grounds on this expedition, with those taken on breeding grounds by others, will contribute to our understanding of the mixing between breeding populations on common feeding grounds in Antarctica,' Dr Gales says.
To complete the picture, genetic analysis of the skin biopsy samples from 64 humpback whales will give scientists an insight into, among other things, the population structure in Antarctic waters, and the sex composition of whales in Antarctica compared to those migrating along the East Australian coast. The team will also use genetic techniques to study age-related gene expression, which could lead to a simple, non-lethal ageing method for baleen whales.Passive acoustic sonobuoys were deployed to identify the sounds produced by whales in the study region and compare them to sounds recorded in other regions of the Southern Ocean. Preliminary analysis of the results has shown that blue whales were the most commonly recorded species and their sounds were similar to those recorded from blue whales at other Antarctic sites. In contrast, humpback whales were rarely recorded, but their limited recordings were intriguing.
'We did record a humpback whale song with the repetition of distinct stereotypic phrases,' Dr Gales says.
'As far as we know, this is the first instance where structured song-like sounds have been recorded from humpback whales on their Southern Ocean feeding grounds. Previously, it was thought that humpback whales only sang during their migration to and from, and while on their breeding grounds.'
The team also recorded a repetitive vocalisation in an aggregation of minke whales, revealing the likely source of a mystery sound.
'Repetitive song-like sounds have been recorded in long term Southern Ocean acoustic datasets, but the source of the "song" has never been identified,' Dr Gales says.
'The bearing to this sound from the sonobuoy was in the same direction that whales were sighted, supporting the likelihood that minke whales are the source of this "song"'.To learn more about the diet of whales, active acoustic instruments (ship-based 'echosounders'), which emit 'pinging' sounds into the water and listen for the returning echo, were used to detect aggregations of krill and small fish in humpback feeding areas. Dense schools of krill – the largest of which was about one kilometre across – were usually found around whale aggregations. Schools of what are thought to be Antarctic silverfish (Pleurogramma antarctica) were also detected around the Balleny Islands. Samples of krill, phytoplankton and small invertebrates (such as salps, amphipods and squid larvae) were collected and their carbon and nitrogen signatures will be compared to those found in the whales' skin biopsy samples to identify the whales' prey and feeding locations.
Dr Gales says the results of the Antarctic whale expedtion will be reported to the International Whaling Commission and shared with other members of the Southern Ocean Research Partnership.
Corporate Communications, Australian Antarctic Division