title: 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.
authors.affiliation: The Key Laboratory of Aquatic Biodiversity and Conservation of Chinese Academy of Sciences, Institute of Hydrobiology of the Chinese Academy of Sciences, Wuhan, China; University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Zhitao
authors.initials: Z
authors.lastname: Wang
authors.forename: Tomonari
authors.initials: T
authors.lastname: Akamatsu
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Mei
authors.forename: Lijun
authors.initials: L
authors.lastname: Dong
authors.forename: Tomohito
authors.initials: T
authors.lastname: Imaizumi
authors.forename: Kexiong
authors.initials: K
authors.lastname: Wang
authors.forename: Ding
authors.initials: D
authors.lastname: Wang
mesh_terms: D000818:Animals; D002681:China; D004455:Echolocation / Q000502:physiology*; D017753:Ecosystem; D005247:Feeding Behavior; D019576:Porpoises / Q000502:physiology*; D011235:Predatory Behavior / Q000502:physiology*; D045483:Rivers; D012767:Ships
keywords: feeding behavior; nocturnal; passive acoustic monitoring; port area; prey availability