2015 Volume 79 Issue 4 Pages 266-276
To estimate the changes in dominant megabenthos catch in relation to dissolved oxygen (DO) concentration in bottom water in Ise Bay, Japan, we conducted a field study with small-bottom trawl. The catch per unit effor (tCPUE) of non-fishery targets increased at 22–36% DO saturation, around the edge of the hypoxic area (approximately less than 10% DO saturation) regardless of the surveys being conducted during day or night. CPUE of fisheries targets was also high at the samehypoxic edge; however, this was indicated only in the nighttime survey for the large catch of the conger eel Conger myriaster. These results indicated that hypoxia of the semi-closed bay induced an avoidance behavior in megabenthos due to the mass non-selective catch of the bottom trawl, but it simultaneously increased the catch. The number of species and the modified Shannon–Wiener diversity index (H*) were positively correlated with DO (%saturation), but not with CPUE. Itwas suggested that the increase of CPUE could be an index of the avoidance behavior in megabenthos in facing to hypoxic water. Both CPUE and economic profits decreased under DO30% saturation and only few megabenthos were caught under DO20%. Different avoidance behavior were taken by the dominant 15 species of non-fishery targets as observed from the different relationships between CPUE and DO saturations. The species that showed relatively slow avoidance against the hypoxia evaluated from CPUE-weighted average DO were goneplacid crab, Carcinoplax vestiva (DO26%; 1.92mg/l); Japanese mantis shrimp, Oratosquilla oratoria (DO30%; 2.24mg/l); and small dragonets, Repomucenus valenciennei (DO30%; 2.21 mg/l). The abnormal distribution and behavior of megabenthos, including that of fishery targets, occurred at higher DO saturation levels than those in experimental LC50 and affected bottom-trawl fishery.
