Passive acoustic survey of Yangtze finless porpoises using a cargo ship as a moving platform

Abstract

In order to periodically investigate the population and distribution of the Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) in its main distribution range in the Yangtze River, a passive acoustic system deployed on a cargo ship as a moving platform, rather than a dedicated research ship, was developed. A stereo acoustic event data-logger (A-tag) was installed on the cargo ship to passively detect phonating animals. In three surveys carried out in the Yangtze River from Wuhan to Shanghai, an average of 6059 clicks in each survey and 284 porpoises in total were acoustically detected along an 1100-km stretch. The animals were detected frequently in most of the survey range except two "gap sections" with 40 and 60 km lengths, respectively, where no animals were detected in all three surveys. Detected group sizes of the animals in each 120-s time window were not significantly different among the surveys, but the distribution pattern was different and suggested seasonal migration. The cargo ship based passive acoustic survey was effective in detecting phonating animals and can potentially monitor the distribution and population trend over time. Compared to surveys that used dedicated research ships, the present method is more cost effective.

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

“…Yangtze River (Zhao et al ; Dong et al ). The average distance between two port areas was 85.5 ± 45.5 km, with minimum and maximum distances of 27 and 157 km, respectively (Table ).…”

“…The discriminating parameters included the minimum number of pulses in a click train, the maximum duration of ICIs between two pulses, and the differences in ICI and SPL between two pulses. Because porpoise sonar always exhibits pulse trains (Au ), the minimum number of pulses in a click train was conservatively set at 5 (Dong et al ; Sasaki‐Yamamoto et al ). Successive clicks were considered as one click train if the ICI was shorter than 200 ms (Akamatsu et al ), because 90% of ICIs were smaller than 276 ms and the occurrence of ICIs near 200 ms was almost negligible in both free‐ranging and tagged finless porpoises (Akamatsu et al ; Akamatsu et al ).…”

Yangtze finless porpoises along the main channel of Poyang Lake, China: Implications for conservation

“…This width was similar to the Yangtze River system; the average width in most regions of the Yangtze River was less than 2 km (Dong et al . ). In addition, the distribution patterns of porpoises with respect to the transect line in both the Yangtze River and Poyang Lake were approximately the same; over 80% of the porpoises were observed in near‐bank areas rather than in mid‐channel areas (Xiao and Zhang , Wei et al .…”

“…) or deploying the A‐tag at the side of a cargo ship (Dong et al . ) to detect the sonar sound of the porpoises. This protocol has also been used at the junction of Poyang Lake and the Yangtze River to reveal the seasonal distribution of the local porpoise population (Kimura et al .…”

Field observation of low-to-mid-frequency acoustic propagation characteristics of an estuarine salt wedge

“…Those few studies carried out in confined coastal and inland waterways that are found in the literature have focused on a variety of issues, including acoustic scintillation to estimate current flow (Di Iorio and Farmer, 1994), active sonar systems for biological stock assessment and fisheries management (Xie, 2000), homeland security applications (Stolkin et al, 2006), acoustical communication (van Walree et al, 2007, acoustical monitoring of tidal bores (Zhu et al, 2010), marine mammal surveys (Dong et al, 2011), seasonal trends in a large remote fjord (McConnell et al, 1992), recreational boat noise in waterways (Haviland-Howell et al, 2007), ambient noise in freshwater habitats (Wysocki et al, 2007), high-frequency noise spectra in shallow brackish water (Poikonen, 2010), long-term noise trends in large, industrialized rivers (Vracar and Mijic, 2011), acoustical monitoring of ship traffic (Fillinger et al, 2011), acoustic attenuation properties in a river (Roh et al, 2008), sitespecific acoustic propagation models for the lower Hudson River Estuary (Radhakrishnan, 2009), and acoustic quantification of stratified turbulence in the Connecticut River (Lavery et al, 2013).…”