Diel variability in catches of major bottom-dwelling fish species in the southwestern part of the Sea of Japan

Abstract

Diel variability in catches of major bottom-dwelling fish species in the southwestern part of the Sea of Japan was analyzed based on survey trawls and fisheries data. Ten pairs of day and night catches were produced by survey trawls at ten sampling points. The catch weight, catch number, occurrence, and standard length were recorded for each species caught by survey trawls. Further, the catch rate and frequency of occurrence in each species were compared between day and night using fisheries data of 487 cases. When the daytime catch rate was over two times higher than the nighttime catch rate, the fish was defined as a daytime species, and vice versa. Based on the results of both analyses, Doederleinia berycoides, Glossanodon semifasciatus, Heterololigo bleekeri, Pagrus major, Takifugu porphyreus, Todarodes pacificus, Uroteuthis edulis, Zenopsis nebulosa, and Zeus faber were classified as daytime species. Conger myriaster, Dexistes rikuzenius, Hippoglossoides pinetorum, and Tanakius kitaharae were classified as nighttime species. Most of the fish species analyzed differed in catch rate between day and night. Therefore, it is necessary to introduce a resource management method and standardization of stock index values based on information about diel variability in catches of each fish species.