Authorities believe a man was mauled and decapitated by a bear in northern Japan after a human head was found near a lake, national media reported this week. An alert for brown bears was issued after the incident.

Police said a fisherman went missing at Lake Shumarinai in Japan's northernmost main island of Hokkaido, Japan's Kyodo news agency reported. Toshihiro Nishikawa, 54, reportedly went to fish by himself on the lake and a boat operator later saw a bear with waders — long rubber boots often worn by anglers — in its mouth.

Officials in the city of Horokanai launched a bear hunt and a member of the search group killed a bear Monday afternoon, Kyodo reported. A human head was also found during the search and authorities were working  to confirm whether the remains belong to Nishikawa.

Police say bear sightings are on the rise this year in Hokkaido, according to public broadcaster NHK. Authorities had received 339 reports as of last Thursday --  40 more than the same period last year, when bears were spotted a record 2,240 times.

Experts say there are likely many reasons for the uptick in human-bear encounters in the region.

"Perhaps the main one is that the bear population of Hokkaido has recovered after years of over-hunting and as there are simply fewer hunters now,"  Kevin Short, a naturalist and professor at Tokyo University of Information Studies, told the South China Morning Post. "The deer population has also recovered, which is a key food source, while there have also been efforts across the prefecture to restore natural habitats in woodlands and along rivers, all of which increases the bears' range."

Two people have been injured in bear attacks in Hokkaido so far in 2023, NHK said.

In 2021, a wild brown bear in Hokkaido injured four people and disrupted flights at an airport before being shot and killed.

Brown bears roam mainly in forests, but experts say they have been increasingly spotted in inhabited areas looking for food, especially during warm weather. In 2020, a town plagued by wild bears in Hokkaido installed robotic wolves to howl at the animals and scare them off.

In:
• Bear
• Japan

Stephen Smith is a senior editor for CBSNews.com.