Partial abundances of three fishery-targeted species of Delphinidae cetaceans (false filler whale, striped dolphin, and Pacific white-sided dolphin) off the Pacific coast of Japan, estimated by the conventional line-transect approach

Abstract

False killer whales, striped dolphins, and Pacific white-sided dolphins have been targeted by dolphin fisheries in the coastal waters off Japan. Annual catch quotas are allocated on the basis of past abundance estimates, but those estimates were unpublished or more than 30 years old. Here, we reanalyzed the line-transect data collected from the sighting survey on the Pacific coast of Japan from 1985 to 2021 and estimated the past and latest abundances of those three species using a standard distance sampling approach. The surveys were conducted as part of the JAFRACSS-SC (Japan Fisheries and Education Agency Cetacean Sighting Survey-Small Cetacean Survey Program). This program mainly targets other fishery-targeted cetacean species and, thus, covers only a part of the above three species’ distribution ranges. As a result, we obtained the latest abundance estimates of 4105 false killer whales, 84,657 striped dolphins, and 28,052 white-sided dolphins. Considering the current estimates represent only a part of the entire population size and that annual catch records did not largely exceed potential biological removals calculated based on these abundances, the current harvest level will not lead to a severe depletion or extinction for these three species.