Warming seas push sharks into Japan’s shallow waters, causing problems for fish farms

And while experts say the species apparently to blame for the uptick in sightings in waters around Kyushu this summer generally pose little threat to humans, they do caution that there has been an increase in “ferocious” tiger sharks in the region.

Japan’s environment ministry on Friday issued heatstroke alerts for 21 of the nation’s 47 prefectures, linking the searing temperatures to the El Nino phenomenon affecting ocean temperatures. Rising water temperatures have been associated with changes in the Black Current, which brings marine life typically found in more southerly latitudes up the east coast of Japan.

A television report by All Nippon News on Wednesday showed the consequences of changing temperatures and currents, depicting sharks breaking through nets surrounding an aquaculture farm in Kinko Bay, an area within the larger Kagoshima Bay. At least two sharks, each around three metres (10 feet) in length, managed to consume amberjack that were nearly ready to be shipped.

Two sharks ultimately died when they became entangled in the net, but around 1,700 amberjack were either eaten or made their way into the ocean through the gaps in the net.

Yosuke Fukami, the owner of Maruyo Suisan, estimated the incident cost the company around 10 million yen (US$62,000).

“We have seen sharks off the port, but never thought they would come so close or to take fish in the nets,” he said. “We are just glad that no humans were injured.”