The Diel Rhythms of Biosonar Behavior in the Yangtze Finless Porpoise (Neophocaena asiaeorientalis asiaeorientalis) in the Port of the Yangtze River: The Correlation between Prey Availability and Boat Traffic

Abstract

Information on the habitat use of the critically endangered Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is critical for its conservation. The diel biosonar behavior of the porpoise in the port areas of the Yangtze River was examined along with simultaneous observations of fish density and boat traffic. Biosonar pulses from the porpoises were detected for 1233 min (5.77%) over a 21,380 min duration of effective observations. In total, 190 (5.63%) buzzes (an indication of prey capture attempts) were recorded among the 3372 identified click trains. Of the 168 echolocation encounters (bouts of click trains less than eight min apart), 150 (89.3%) involved single animals, indicating that solitary porpoises were frequently present and feeding in the port areas. Significant diel patterns were evident involving the biosonar behavior of the porpoises (including click trains and buzzes), fish density and boat traffic. The frequencies of the click trains and buzzes were significantly lower during the day than in the evening and at night, which suggests that porpoises in this region are primarily engaged in crepuscular and nocturnal foraging. The lack of a significant diel pattern in the echolocation encounters indicates the importance of the port in porpoise conservation. A forced feeding schedule may be associated with the lack of a significant correlation between porpoise acoustics and boat traffic. Overall, prey availability appears to be the primary factor that attracts porpoises. Additionally, porpoises tend to migrate or remain downstream in the morning and migrate or remain upstream in the evening, most likely to follow their prey. The findings of this study can be used to improve the conservation of the Yangtze finless porpoise.

Fine‐scale habitat use in Indo‐Pacific humpback dolphins, Sousa chinensis, may be more influenced by fish rather than vessels in the Pearl River Estuary, China

“…Furthermore, fewer dolphins were detected within an area with fewer fish choruses, despite the significantly lower vessel presence. Previous studies on Yangtze finless porpoises have also reported high detection rates in areas where vessel, but also fish activity, was greater (Kimura et al 2012, Wang et al 2014, 2015a); for which forced-feeding was the offered explanation (Wang et al 2014(Wang et al , 2015a. While the findings within the current study may suggest Indo-Pacific humpback dolphins might be demonstrating a degree of tolerance for vessels due to foraging pressure, more data are needed to strengthen such an argument for Indo-Pacific humpback dolphins within the current study.…”

“…, ); for which forced‐feeding was the offered explanation (Wang et al . , ). While the findings within the current study may suggest Indo‐Pacific humpback dolphins might be demonstrating a degree of tolerance for vessels due to foraging pressure, more data are needed to strengthen such an argument for Indo‐Pacific humpback dolphins within the current study.…”

“…, Wang et al . , ). Previous studies have also suggested low site fidelity in dolphins may be caused by lower prey availability (Grigg and Markowitz ), including humpback dolphins off South Africa and Mozambique (Karczmarski et al .…”

The spatial pattern of larval fish assemblages in the lower reach of the Yangtze River: potential influences of river–lake connectivity and tidal intrusion

“…Meanwhile, the finless porpoise was observed to be more abundant in the river section up and down the mouth of Poyang Lake than in other parts of the river (Kimura et al, 2012). The availability of prey fish is suggested as a major factor influencing the distribution of the finless porpoise (Wang et al, 2014). Dominant species of larval fish collected in the present study, such as H. bleekeri, P. pekinensis, and Hemiculter Leucisculus (Basilewsky, 1855), are assumed to be potential prey fishes for this animal (Yu et al, 2002).…”

The impact of fisheries management practices on the survival of the Yangtze finless porpoise in China

“…Even if fishers generally do not intend to catch or harm porpoises on purpose (Turvey et al, ), unintentional injuries to porpoises may result from the animals becoming entangled or interacting with gear underwater. Yangtze finless porpoises have been shown to be primarily nocturnal and crepuscular feeders, and are more active during the night and at dawn (Akamatsu, Wang, Wang, Li, & Dong, ; Kimura et al, ; Wang, Akamatsu, Wang, & Wang, ). The potential temporal overlap between the porpoise foraging time and the illegal fishing time may therefore lead to a higher risk of collateral damage to porpoises (Jefferson & Curry, ).…”