Ayu Fry Catch in Lake Biwako Plummets to Record Low
The January haul of ayu sweetfish from Lake Biwako, Japan's largest lake, was a mere 3% of the average, marking the lowest catch since record-keeping began in 2009. This alarming decline is attributed to poor spawning conditions caused by the scorching heatwave experienced last summer.
The ayu, a representative fish species of the landlocked Shiga prefecture, constitutes roughly half of the total fish catch from Lake Biwako. The fishing season for ayu fry, known as "hiuo" (ice fish), commences in December. Traditionally, a maze of netting called "eri" is fixed in the water to capture hiuo during winter and early spring.
A study conducted on 14 eri nets, representing half of all nets operated by fisheries cooperative associations, revealed a dismal average catch of 4.3 kilograms per eri in January. This figure stands at a mere 2.9% of the average catch of 149 kg per net recorded over the past decade.
The extreme heatwave that persisted through September last year resulted in a 2-degree increase in the water temperature of rivers flowing into Lake Biwako during the ayu spawning season of September and October. This, coupled with low rainfall, led to a significant decrease in river water volume. Consequently, the number of ayu eggs found between August and October last year was a mere 20% of the average for that period.
Despite the low catch, a fishery experiment station observed a relatively normal number of ayu shoals in January. The Shiga prefectural government is currently investigating the discrepancy between the observed shoal size and the low catch.
The low water level in Lake Biwako, which has persisted since autumn, prompted the establishment of a drought management headquarters in January for the first time in 18 years. While no direct link has been established between the drought and the poor catches, fishermen report that the altered water currents caused by the low water level have disrupted the usual migration patterns of ayu, impacting their catch.
The poor catches have resulted in fisheries cooperative associations being unable to fulfill orders placed by ayu breeders, leading to shipment delays to retailers and restaurants. The situation has caused significant financial hardship for fishermen, some of whom have been forced to suspend operations due to the lack of profitability.