Dead fish a mystery

Thousands of dead fish have been washing up on Rodney beaches.

Martins Bay residents woke up Thursday to the sight of many dead sprats or pilchards along their beach, with more found at Stanmore Bay and Orewa Beach days later.

Dog walkers were reluctant to let their pets touch the fish in case they were poisoned.

Experts are at a loss to explain the mass deaths but doubt they are the result of toxins. Some of the dead fish have been sent to the Fisheries Ministry for analysis.

Rough weather or predators may have been factors.

The fish may have been chased into the shallows by predators, Conservation Department spokeswoman Thelma Wilson says.

They could also have been scared ashore by the southern right whale and calf off Rodney’s east coast, seen late last week at Waiwera.

The 18-metre whale has moved into the Mahurangi Harbour after a week at Waiwera. The department took DNA samples from the mother and calf.

While there were public concerns about the whales beaching Ms Wilson says they have no fears of that since the whales are used to shallow waters.

Leigh Marine Laboratory ecology lecturer Richard Taylor agrees predators could explain the deaths, saying kingfish, dolphins and kahawai feed on this type of fish.

Honorary fisheries inspector Murray Little says no trawling activity was apparent and the fish were unlikely to have been killed by a toxic algae bloom, which can occur in calm, warm weather.

He says the fish are pilchards and could have died after their gills filled with fine silt whipped up by the July 11 storm. Mr Little estimates about 1500 fish washed up at Martins Bay.

He sent samples off for testing but with a backlog of samples the ministry says it will test them as soon as possible.

Unusual sightings such as the fish deaths should be reported to the biosecurity hotline on 0800-80-99-66.