Antarctic voyage seeks to uncover whales’ secrets
Searching for answers in a vast ocean may seem a daunting task, but scientists are relying on sound rather than sight in the latest hunt for whales.
The scientists on board Niwa’s Tangaroa, which left Wellington yesterday on a six-week voyage to Antarctica, will be retrieving underwater moorings that have recorded sounds for the past two years. From those, they are hoping to learn more about the behaviour of sperm whales.
Niwa marine ecologist Dr Matt Pinkerton said sightings of the vulnerable species had been rare in recent years.
Sperm whales were targeted by the whaling industry in the 19th and 20th centuries, and more than 70 per cent of their population was wiped out.
‘‘My theory is that because of all the whaling that took place, they’ve learned to disappear as soon as they hear a big ship.’’
Knowing how many sperm whales were in the Ross Sea, and their movements, was an important part of a five-year programme, led by Niwa, to monitor the effectiveness of the Ross Sea Marine Protected Area established in 2017.
The first stage of the programme was to establish baselines for future comparisons to determine the effects of fishing and climate change.
‘‘We don’t really know their annual cycle – where their populations are concentrated and how different groups of whales interact,’’ Pinkerton said.
Sperm whales could dive to 3000 metres, and most toothfish (important prey for the whales) were at 1000m, well within diving range.
The abundance of toothfish on the Ross Sea slope had been reduced by fishing, and scientists wanted to know if that had affected sperm whales.
The best way to count them was via acoustic moorings, which recorded the sounds they made, sound travelling easily over great distances underwater.
Niwa marine mammal acoustician Dr Giacomo Giorli has been working on the project since its inception in 2017.
The initial moorings – at Iselin Bank, the Pacific-Antarctic Ridge, and Scott C seamount – were deployed in the summer of 2018 for 12 months. One was unable to be retrieved but the others provided a year’s worth of data.
They were replaced with three others, which had now been in the water for two years.
Sperm whales made a distinctive ‘‘short snapping sound’’, making them one of the easiest marine mammals to recognise sonically.
The moorings recorded sound for three minutes every 12 minutes.
‘‘What we look for is the echo location sound. It travels through the water and bounces off an object.’’
Foraging sperm whales typically sent one sound every second while searching for prey but increased the rate the closer they got to their target.