Identification of fishing gear entangled around the tail of a stranded sperm whale

This study reports the relationship between specific fisheries and an individual's incidental catch by focusing on a calf sperm whale (SNH21048) that was stranded with a fishing net.The net was primarily found entangled around the whale's tail and was removed using mechanical cutting.The separated fishing gear was observed to include a diamond-shaped net, a headrope with floats, a footrope with a lead core, and foam fishing buoys, suggesting that the gear could be broadly classified as a drift net.The fishing gear was characterized by a nylon multi-monofilament, a 175 mm mesh size designed to target larger species, and a footrope with a lead core, similar to the gear used in the drift-net fishery for billfishes operating in waters from the Boso Peninsula to eastern Hokkaido.Based on AIS data from the fishery, the fishing grounds were observed as the western and eastern areas off Erimo, which are relatively close to the stranding sites.This individual was alive at the time of discovery, suggesting that the entangling net was relatively short (40 m), resulting in minimal drag and buoyancy effects on its behaviour, and/or that the net was entangled in waters near the point of stranding, meaning the whale wasn't exposed to the effects of entanglement for an extended period.