Overfishing has been blamed for an “alarming” drop in dolphin numbers, with fears their populations may be at just 13 per cent of what they were in 1980.

An international group of scientists — including from Queensland’s James Cook University — used the numbers of dolphins caught accidentally in fishing nets as a way to estimate the wider population present in the world’s oceans.

Tens of thousands of dolphins are snared in nets each year.

The researchers found the numbers of dolphins snared had decreased by one-fifth since 2004, a sign of a rapid decrease in the number of dolphins in the ocean.

“The declining cetacean bycatch rates shown by what we can measure suggest current mortality rates are not sustainable,” said James Cook University’s Dr Putu Mustika, one of the researchers involved…