Fishermen and tourist operators have asked the government to tackle the problems of unusually cool Andaman Sea currents and a "red tide" of plankton.

Boonthin Changnam, a fisherman from Koh Lanta in Krabi, admitted he did not know what the government could do, since there was "no culprit" for the phenomenon that has caused massive fish losses over the past month.

Thorn Thamrongnawasawadi, a marine biologist, said the death of fish was caused by two factors - both consequences of the El Nino phenomenon.

The first was the bloom of plankton caused by the sea's high surface temperatures. The second was that cold currents in the depths of the sea had driven deep ocean fish to swim up to the warmer water on the surface. Some fish had died from "shock" from the change of temperature, while others had died from plankton "poisoning".

Boonthin said his catch had dropped from 100 kilograms per week to about 40 to 50 kilograms.

Meanwhile, Harin Lohprasongkij, secretary of Krabi Fishing Association, said commercial boats equipped with hi-tech fishing gear had actually caught more fish. "We are not happy catching more, since it is too many and we are afraid it will cause long-term negative impacts," he said.

According to Harin, since the phenomenon began a month ago, about 200,000 kilograms of mackerel were being caught daily by all commercial boats in the province. Normally, they caught less than 100,000 kilograms.

Vichai Rattamanee, chairman of Trang's Tourism Business Association, said yesterday that many tourists panicked when they saw dead fish floating. He was afraid that the phenomenon would damage tourism.