Thousands of herbivorous milkfish washed into the sea from fish farms along the coast of Greater Tainan by flooding caused by Typhoon Morakot in 2008 may have changed their feeding habits and they seem to have begun eating other species of fish, an Academia Sinica research fellow said recently, warning of a possible disruption in the balance of marine life.
Nicknamed “seaweed fish” by fishermen from southern Taiwan, milkfish generally feed on algae and seaweed, said Jeng Ming-shiou (鄭明修), a researcher at Academia Sinica’s Research Center for Biodiversity.
“However, in order to survive in the wild, the huge shoals of farm-grown milkfish may have become omnivorous and begun preying on silver anchovy after being swept into the sea,” Jeng said.
Jeng said he reached this conclusion after large numbers of milkfish were reported in waters near Penghu and Green Island (綠島), where they had not been spotted before the typhoon.
Furthermore, milkfish found in those areas not only have a higher survival rate, but are also larger, with some reaching 80cm in length, more than twice the length they usually grow to, Jeng said.
Jeng added that a fisherman from Greater Kaohsiung even reported catching a milkfish measuring 160cm in length.
“By contrast, the numbers of silver anchovy in the same areas have greatly diminished in the same timeframe, which I believe is evidence of the milkfish’s changing feeding habits,” Jeng said.
Jeng called for further research on the matter.
Echoing Jeng’s theory, Tsai Chu-fu (蔡居福), a veteran fisherman from Green Island, said that seabirds, that can usually be seen preying on silver anchovy in waters surrounding the island between June and July each year, were surprisingly nowhere to be seen in 2011.
“In addition, we had never seen a single milkfish in these areas before Typhoon Morakot, but ever since large shoals have been repeatedly spotted, with some fish weighing up to 8kg,” Tsai said.
Dismissing these concerns, Fisheries Agency Deputy Director-General Tsay Tzu-yaw (蔡日耀) said that although he was unfamiliar with Jeng’s research, milkfish were not likely to feed on silver anchovy.
“To my knowledge, local authorities or fishermen have not reported a decrease in hauls of silver anchovy. Even if the silver anchovy population has declined, it is most likely attributable to the changing marine environment,” Tsay said.