NZ great white shark stock worries scientists

New shark research shows the great white shark population of New Zealand is even lower than expected.

The study used genetic analysis to estimate the total number of adults in the eastern population at just 750.

The eastern population includes New Zealand, the east coast of Australia and some of the south Pacific. Including juveniles, the estimated total population size is only 5,460.

Scientists from the Department of Conservation (DoC) and National Institute of Water and Atmospheric Research (NIWA) contributed to the study, which was published on Thursday in the scientific journal Nature Scientific Reports.

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 worrying.

"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," Mr Duffy says.

"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."

It's the first time it's been possible to estimate the total number of adults in the New Zealand white shark population.

"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.

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.


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