Research published yesterday in scientific journal Nature Scientific Reports, and updated with new samples and analyses, estimates that the total number of adult white sharks across the Australasian region is only around 2,210.
The research was led by scientists from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Hobart. Scientists from the DOC and National Institute of Water and Atmospheric Research (NIWA) contributed to the study. They provided genetic samples from white sharks tagged near Stewart Island, Chatham Islands and the New Zealand mainland, and from sharks accidentally caught by fishers.
DOC's marine technical advisor Clinton Duffy says the research is significant because it's the first time that it has been possible to estimate the total number of adults in the New Zealand white shark population.
The total number of adults in the 'Eastern' population, which includes New Zealand, is estimated to be about 750. Adding juveniles to the equation results in an estimated total population size of 5,460.
"We had assumed the population was low because of the slow breeding and growth rate of white sharks, but the numbers are a bit lower than we thought," he says.
White sharks migrate seasonally between New Zealand, Australia and the islands of the south-west Pacific. Their threat classification status in New Zealand waters was assessed in 2005 as "Declining".
"This new information shows how vulnerable the species is. The main threats to white sharks in New Zealand waters are through accidental by-catch in fisheries, particularly for small juvenile sharks on long lines and adults in set nets."
"Estimating the abundance of large sharks is difficult because the tools normally used by fisheries scientists, like trawl surveys, acoustic surveys or tag-recapture experiments, don't work well for them," says Malcolm Francis, NIWA Principal Scientist. "This new genetic technique offers strong promise for monitoring rare and threatened species".
Dr Francis says that NIWA and DOC have been jointly studying white sharks in New Zealand for more than 10 years, and the opportunity to collaborate with our Australian colleagues in this study is an important breakthrough in understanding the status of the Australasian white shark population.
White sharks are absolutely protected in New Zealand waters and if people accidentally catch one they must release it immediately alive and unharmed, and are required to notify DOC.