Sperm whales found off North Island
New Zealand scientists have found sperm whales feeding in deep canyons off the lower North Island. Niwa researchers Giacomo Giorli and Kimberly Goetz expected to find them in these locations because the sperm whales are known to hunt in canyons, the locations aren’t that far from Kaiko¯ ura – where sperm whales have been studied extensively – and because old whaling records show sperm whales were taken in the Cook Strait region.
But knowledge on sperm whales in New Zealand waters is still thin and gappy.
Sperm whales were not much expected off the Taranaki coast, for example, because of the relatively shallow waters.
So whale experts were somewhat surprised when about a dozen sperm whales stranded on remote Taranaki beaches in May last year.
And knowledge of solitary sperm whales off Fiordland comes from observations made by Japanese fishing vessels decades ago.
Today, the number of sperm whales in New Zealand waters is unknown.
Studies carried out between 1988 and 1993 off Kaiko¯ ura
estimated 60-108 animals. But a study this year found that the population was in decline.
Sperm whales were moved from ‘‘not threatened’’ to ‘‘data deficient’’ in the Department of Conservation’s 2019 statement on the Conservation Status of NZ Marine Mammals.
For their work, Goetz and Giorli gathered data from three passive acoustic monitoring recorders moored to the sea floor. One was northwest of Kaiko¯ ura, the second was off Cape Palliser, the southernmost point of the North Island, and the third was east of Te Awaiti on the lower east coast – all of them in deep water.
From June 2016 to August 2017, they recorded 53,823 ‘‘echolocation click trains’’ from sperm whales.
Echolocation is when sperm whales emit sounds and listen to the echoes bouncing back from objects such as prey. It’s how they locate food in the dark, deep-sea environment.
These whales echolocate when they dive. A bottom phase follows, also characterised by clicks and is usually associated with feeding. The whales then ascend to the surface in a silent phase.
An algorithm was written to filter out all other noise.
Apart from confirming sperms whales were active off the south coast of the North Island, the data set showed they were foraging day and night and year round. They also recorded more feeding activity in the southern Kaiko¯ ura region compared to the two further north.
Giorli and Goetz did not count the number of sperm whales, although that could be done.
The three monitors were part of a larger Niwa programme in the Cook Strait area that recorded the entire underwater soundscape. It produced 14 terabytes of acoustic data.
Last year, Goetz and Giorli reported on the presence of beaked whales in the area using data from the programme.
There’s considerable data yet to be processed and is reliant on funding and time.
Sperm whales (para¯ oa, Physeter macrocephalus) are toothed whales and found in all of the world’s oceans, from polar waters to the Equator.
In New Zealand waters, they mainly eat various squid species, as well as fish such as groper, ling, orange roughy and southern kingfish.
The sperm whale paper was published in the journal Scientific Reports.
Knowledge on sperm whales in New Zealand waters is still thin and gappy.