An ayu fry, known as "hiuo" or ice fish due to its translucency, is a popular fish species in Japan's Shiga prefecture, accounting for about half of the entire fish catch from Lake Biwako. The January catch of ayu sweetfish from the lake was alarmingly low at only 3 percent of the average, attributed to poor spawning likely caused by the scorching heat experienced the previous summer, according to officials from the Shiga prefectural government's Fisheries Management Division.
The low ayu catch has been a significant concern for local fishermen, with one fisherman from the Shigacho fisheries cooperative expressing that the current situation is unprecedented in his 40-year career. The fishing season for ayu fry, called "hiuo," usually opens in December, with a traditional method involving a maze of netting called "eri" set up in the water during winter and early spring to catch ice fish. Despite operating 12 eri, the most in the prefecture, the average January catch per eri was only 4.3 kilograms, significantly lower than the mean catch of 149 kilograms per net averaged over the past 10 years.
Extreme heat lasting through September the previous year, leading to higher water temperatures in rivers flowing into Biwako and low rainfall, has been identified as contributing factors to the poor ayu catches. The situation has been exacerbated by a decrease in river water volume and a lower number of ayu eggs found, impacting the fish population in Lake Biwako. Despite a smaller number of observed ayu shoals this year compared to an average year, the prefectural government is conducting further studies to determine the reasons behind the dwindling ayu catch. The situation has been so severe that the prefectural government set up a drought management headquarters for the first time in 18 years in January, although no confirmed causal relation between the drought and poor catches has been established.