Anthropogenic activity, hydrological regime, and light level jointly influence temporal patterns in biosonar activity of the Yangtze finless porpoise at the junction of the Yangtze River and Poyang Lake, China

Abstract

Under increasing anthropogenic pressure, species with a previously contiguous distribution across their ranges have been reduced to small fragmented populations. The critically endangered Yangtze finless porpoise ( Neophocaena asiaeorientalis asiaeorientalis ), once commonly observed in the Yangtze River-Poyang Lake junction, is now rarely seen in the river-lake corridor. In this study, static passive acoustic monitoring techniques were used to detect the biosonar activities of the Yangtze finless porpoise in this unique corridor. Generalized linear models were used to examine the correlation between these activities and anthropogenic impacts from the COVID-19 pandemic lockdown and boat navigation, as well as environmental variables, including hydrological conditions and light levels. Over approximately three consecutive years of monitoring (2020–2022), porpoise biosonar was detected during 93% of logged days, indicating the key role of the corridor for finless porpoise conservation. In addition, porpoise clicks were recorded in 3.80% of minutes, while feeding correlated buzzes were detected in 1.23% of minutes, suggesting the potential existence of localized, small-scale migration. Furthermore, both anthropogenic and environmental variables were significantly correlated with the diel, lunar, monthly, seasonal, and annual variations in porpoise biosonar activities. During the pandemic lockdown period, porpoise sonar detection showed a significant increase. Furthermore, a significant negative correlation was identified between the detection of porpoise click trains and buzzes and boat traffic intensity. In addition to water level and flux, daylight and moonlight exhibited significant correlations with porpoise biosonar activities, with markedly higher detections at night and quarter moon periods. Ensuring the spatiotemporal reduction of anthropogenic activities, implementing vessel speed restrictions (e.g., during porpoise migration and feeding), and maintaining local natural hydrological regimes are critical factors for sustaining porpoise population viability.

Temporal and spatial biosonar activity of the recently established uppermost Yangtze finless porpoise population downstream of the Gezhouba Dam: Correlation with hydropower cascade development, shipping, hydrological regime, and light intensity

“…In this investigation, the significantly higher biosonar activity at night than during the day was consistent with that observed in the Pengze area of the Yangtze River (Wang et al, 2014), in the confluence area between Poyang Lake and the Yangtze River (Duan et al, 2023) and in the Wuhan section of the Yangtze River (Wang et al, 2024). The circadian rhythm of biosonar activity in finless porpoises observed in this study did not exhibit as pronounced a pattern compared to that documented in the confluence area between Poyang Lake and the Yangtze River (Duan et al, 2023).…”

“…TA B L E 2 (Continued) are porpoise positive was 64% for the three sites downstream of the Gezhouba Dam, which is less than what was reported between the confluence of Poyang Lake and the Yangtze River (93%) (Duan et al, 2023) and higher than that reported in the Wuhan region of the Yangtze river (43%) (Wang et al, 2024). However, porpoise buzz signals account for 78% of all porpoise click trains over the pooled data of the three study sites, which is significantly greater than that recorded between the confluence of Poyang Lake and the Yangtze River (23%) (Duan et al, 2023) and in the Wuhan region of the Yangtze river (55%) (Wang et al, 2024).…”

“…The MZ site was situated at the junction of two rivers beneath the Gezhouba Dam. Yangtze finless porpoises were frequently spotted aggregating at confluence areas where prey biomass and availability were greatest (Duan et al., 2023 ; Zhang et al., 1993 ). The finless porpoises in the Yangtze is an opportunistic predator (Kimura et al., 2012 ).…”

“…Using custom‐made Python software, the hydrological regime of the water level and water flow at the acoustic monitoring location was collected from the official database of the water resources database ( https://slt.hubei.gov.cn/sjfb/ ). In order to study diel patterns, each day was divided into three light periods: darkness, twilight, and day (Duan et al., 2023 ; Narganes Homfeldt et al., 2022 ). In order to investigate lunar trends, nighttime was separated into three periods: the new moon, the quarter moon, and the full moon (Wang, Nachtigall, et al., 2015 ).…”

“…cn/ sjfb/ ). In order to study diel patterns, each day was divided into three light periods: darkness, twilight, and day (Duan et al, 2023;Narganes Homfeldt et al, 2022). In order to investigate lunar trends, nighttime was separated into three periods: the new moon, the quarter moon, and the full moon (Wang, Nachtigall, et al, 2015).…”