Nineteenth-century whaling logs – chronicles of systematic slaughter – are now helping to protect southern right whales. NIWA scientists pored over pages of grim reapings that nevertheless held valuable clues to the whales’ present-day behaviour and distribution.
Funded by the Australian Marine Mammal Centre, the scientists spent three years analysing historic documents – compiled by the World Whaling History project – to deduce habitats where the nationally endangered species may still be at risk from shipping traffic and climate change.
Australian Marine Mammal Centre website
“The data proved an absolute goldmine,” says NIWA Marine Ecologist Dr Leigh Torres. “There is very little modern information on the offshore habitats of southern right whales. The historic documents are derived from vessel log books dating from between 1825 and 1888, in which whalers recorded their daily location and encounters and strikes of whales. They identify about 1800 locations where whale strikes or sightings occurred and – importantly – indicate about 23,000 places where whalers searched for, but failed to find, their target.”
There were once some 27,000 southern right whales in New Zealand and Australian waters. But their slow speed and superior oil yield, plus their handy trait of floating once harpooned, made them the ‘right’ whales to pursue. At their nadir in 1913, as few as 14 survivors may have remained around New Zealand and, despite 65 years of official protection, species’ recovery has been slow, hampered by a slow reproduction rate.
By combining historic data with present-day oceanographic information, sophisticated computer modelling helped the researchers predict the wanderings of the estimated 900 individuals alive today.
“We identified a number of consistent and influential predictors of whale distribution,” Torres says. “For example, the data showed that the southern right is very sensitive to ocean temperature, and has a distinct upper limit.”
That led the team to predict how climate change might alter the species' habitat and range. When ocean temperature projections for 2090–2100 were fed into the distribution model, says Torres, “substantial shifts in whale habitat suitability and availability in the Australasian area were indicated”.
They also fed in shipping traffic data, which shed light on those parts of the whales’ range and migration routes where they could be at greater risk from vessel strike. “We identified two areas – one on the Chatham Rise east of New Zealand and one in the waters south of Australia – where busy shipping lanes intersect key whale habitats,” says Torres.
Published in the journal Diversity and Distributions, the results, she says, will “form an important basis for future management and conservation efforts,” and validate unconventional datasets, such as historical exploitation data, as tools to predict present-day species distribution.
“We’re confident in the predictive capacity of our models, and we’re now familiar with the nuances of the historical information, so it’s possible we could apply this technique to the entire Southern Hemisphere – and to other species of whale.”