Distribution Pattern of the East Asian Finless Porpoise in the Huanghe River Estuary and Its Adjacent Waters in Spring

Abstract

The East Asian finless porpoise (EAFP, Neophocaena asiaeorientalis sunameri) is the exclusive cetacean species commonly seen in Bohai Sea. It was listed as Grade II in the latest updated list of wild animals under priority state conservation, and listed as the endangered in the latest International Union for Conservation of Nature Red List of Threatened Species. The Huanghe (Yellow) River estuary and its adjacent waters is an important habitat for EAFPs. However, knowledge on its distribution pattern in this area is particularly scarce, which hindered its conservation process. Therefore, passive acoustic monitoring (PAM), including towed PAM and fixed PAM, were conducted in June in 2019 and 2021 in the study region to gain information of spatial distribution of EAFP and the pattern of soniferous fishes. Results reveal that EAFPs were selective in their use of the waters in spring in heterogeneous distribution: higher acoustic encounter densities were observed in the northern part of the estuary and the central of Laizhou Bay than those in the southern part of the estuary and the western part of Laizhou Bay. In further analysis, two types of fish calls were found in the northern Huanghe River estuary and central Laizhou Bay only. Particularly, fish choruses were recorded in the central Laizhou Bay, indicating a high soniferous fish abundance. This study provides insights into the distribution pattern, habitat selection, and potential impact factors of the EAFPs in spring in the Huanghe River estuary and its adjacent waters, highlighting the importance of underwater anthropogenic noise and soniferous fish resource managements for local authorities tasked with protecting this endangered cetacean.