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 drastic decline is attributed to poor spawning conditions caused by the scorching heat experienced last summer.
The ayu, a representative fish species of the landlocked Shiga prefecture, typically accounts for about 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 represents a mere 2.9% of the average catch of 149 kg per net recorded over the past decade.
The extreme heat 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 and a reduction in the number of ayu eggs found by 80% compared to the average.
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 poor catch.
The low water level in Lake Biwako, which prompted the establishment of a drought management headquarters in January, has also raised concerns. While no direct link between the drought and the poor catch has been established, fishermen have reported changes in water currents around the eri nets, potentially affecting the movement of ayu.
The poor catches have resulted in difficulties fulfilling orders placed by ayu breeders and delays in shipments to retailers and restaurants. The situation has caused significant financial strain on the fisheries cooperative associations and individual fishermen.