Frequent and prolonged nocturnal occupation of port areas by Yangtze finless porpoises (Neophocaena asiaeorientalis): Forced choice for feeding?

Abstract

During the Yangtze Freshwater Dolphin Expedition 2012, Yangtze finless porpoises (Neophocaena asiaeorientalis) were acoustically monitored in 9 port areas at night. During 6566 min of nocturnal monitoring, porpoise sonar was detected for 488 min (7.43% of the total time). Of all 81 encounters, the longest echolocation span obtained was 102.9 min, suggesting frequent and prolonged porpoise occupation of the port areas. A combined total of 2091 click trains were recorded, with 129 (6.2%) containing minimum inter-click intervals (ICIs) below 10 ms (termed a buzz). Buzzes with a decrease in ICIs and search and approach phases that resembled feeding echolocation signals accounted for 44.2% (N = 52) of all buzzes. Buzzes with an increase in ICIs, suggesting a mirrored prey capture phase, accounted for 20.2% (N = 26) and could reflect attempts to locate escaped prey because they were followed by approach-phase feeding buzzes. Anecdotal evidence of porpoises fleeing the proximity of vessels was observed. The recordings indicating clusters of porpoises feeding near the port areas suggest a forced choice for feeding due to the relatively higher prey availability in the port areas compared to other areas in the Yangtze River that are probably overfished.

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 .…”

A preliminary study on diet of the Yangtze finless porpoise using next‐generation sequencing techniques

“…), as has the tendency of porpoises to forage within port environments, where they also display boat avoidance behavior (Wang et al . ). These facts together suggest that Yangtze finless porpoises experience food shortages in Yangtze River, and that they are forced to forage in unfavorable environments (Wang et al .…”

“…These facts together suggest that Yangtze finless porpoises experience food shortages in Yangtze River, and that they are forced to forage in unfavorable environments (Wang et al . ). However, the diet of the Yangtze finless porpoise has been poorly known for a long time because of the lack of studies of stomach contents.…”