Pollution poses threat to Hector’s dolphin

Press, 2 June 1989, Page 34

Pollution poses threat to Hector’s dolphin

By

NIGEL MALTHUS

Pollution as well as gillnetting is threatening the endangered Hector’s dolphin population around Banks Peninsula.

Concern over pollution has been raised by two Canterbury University doctoral students, Ms Elizabeth Slooten and Mr Stephen Dawson, whose warnings over the endangered species’ vulnerablity to nets has already led to the establishment of a marine mammal sanctuary in Banks Peninsula waters.

In a report published recently by the United States Marine Mammal Commission, the researchers said the dolphin’s preference for living near the shore also made them vulnerable to pollutants such as heavy metals and pesticide residues.

"Although the biological effects of the pollutants are poorly known, the level of contaminants found in dolphin tissues examined to date gives cause for concern,” said the report. The pollutants were not central to their investigations, but the pair have had tissue samples analysed when available throughout their four-year study of the dolphins for their zoology Ph.D. theses.

Ms Slooten said yesterday that they had found maximum levels of DDT of 52.85 parts per million, and maximum levels of mercury of 51.18 ppm. That put them “somewhere in the middle” between animals in clean waters and those such as the “outrageously” contaminated beluga, a small

white whale living in the St Lawrence Seaway, said Ms Slooten. She said that, according to some studies, anything between 50 and 500 ppm of DDT was regarded as high. Readings as low as 0.18 ppm have been found in blue whales in the Antarctic, and readings between 450 and 1831 ppm have been recorded in common dolphins in the Mediterranean Sea. For mercury, readings of between five and 200 ppm indicated a polluted region. Other dolphin species around New Zealand had levels between 37 and 72 ppm, said Ms Slooten.

Mr Mike Donaghue, of the Department of Conservation, said the beluga of the St Lawrence Seaway was so riddled with contaminants that if their corpses wash up on shore they cannot be casually buried but must be treated as toxic waste. Mr Donoghue said New Zealand waters were wellknown for relatively high levels of heavy metals such as mercury, cadmium and zinc, because the country was geologically young, with high levels in the soil, brought up by volcanic action.

It was debatable how much of the heavy metals occurred naturally and how much came from accelerated leaching into the sea from human activities like mining, he said.

Because New Zealand was an agricultural country, Hector’s dolphins were probably as exposed to pesticide residue as cetaceans (whales, dolphins and porpoises) anywhere in the world, said Mr Donaghue.