The January haul of ayu sweetfish from Lake Biwako was a mere 3% of the average, marking the lowest catch since record-keeping began in 2009. Officials attributed the poor catch to poor spawning conditions caused by the scorching heat of the previous summer.
The ayu, a prized fish species in Shiga Prefecture, constitutes approximately half of the total fish catch from Lake Biwako. The fishing season for ayu fry, known as "hiuo" (ice fish), commences in December.
Traditionally, hiuo are caught using a maze of netting called "eri" fixed in the water during winter and early spring. The Shigacho fisheries cooperative association operates the most eri in the prefecture, with 12 nets.
A study of 14 eri revealed an average January hiuo catch of 4.3 kilograms per net, a mere 2.9% of the 10-year average of 149 kg per net. This figure was even lower than the 6.5 kg catch in January 2017, when excessive spawning led to a record-poor catch.
Extreme heat persisted through September 2022, resulting in elevated water temperatures in rivers flowing into Lake Biwako during the ayu spawning season. The number of ayu eggs found during that period was only 20% of the average.
Despite the low catch, a fishery experiment station observed approximately 20% as many ayu shoals as in an average year. The prefectural government is investigating the discrepancy between the observed shoals and the poor catch.
The low water level in Lake Biwako, which prompted the establishment of a drought management headquarters in January, may have also contributed to the poor catches. Fishermen have reported that the altered water currents have affected the movement of ayu, making them less likely to encounter the eri nets.
The poor catches have impacted fisheries cooperative associations, which have been unable to fulfill orders from ayu breeders and retailers. The Shigacho fisheries cooperative fisherman expressed concern about the financial implications of the situation, stating that some fishermen have suspended operations due to the low profitability.