Indirect Evidence of Boat Avoidance Behavior of Yangtze Finless Porpoises

Li, Songhai; Akamatsu, Tomonari; Wang, Ding; Wang, Kexiong; Dong, Shouyue; Zhao, Xiong; Wei, Zhao; Zhang, Xianfeng; Taylor, Barbara L.; Barrett, Leigh A.; Turvey, Samuel T.; Reeves, Randall R.; Stewart, Brent S.; Richlen, Michael; Brandon, John R.

doi:10.1080/09524622.2008.9753806

Cited by 16 publications

(24 citation statements)

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“…Dive time in marine mammals can be affected by physiological factors, such as oxygen storage and consumption [64], as well as external factors such as presence of vessel traffic [65], [66]. A recent study of Ganges River dolphins [47] found that time of day did not significantly affect dive time, although this study was based on limited survey effort.…”

Section: Discussionmentioning

confidence: 99%

To See or Not to See: Investigating Detectability of Ganges River Dolphins Using a Combined Visual-Acoustic Survey

et al. 2014

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Detection of animals during visual surveys is rarely perfect or constant, and failure to account for imperfect detectability affects the accuracy of abundance estimates. Freshwater cetaceans are among the most threatened group of mammals, and visual surveys are a commonly employed method for estimating population size despite concerns over imperfect and unquantified detectability. We used a combined visual-acoustic survey to estimate detectability of Ganges River dolphins (Platanista gangetica gangetica) in four waterways of southern Bangladesh. The combined visual-acoustic survey resulted in consistently higher detectability than a single observer-team visual survey, thereby improving power to detect trends. Visual detectability was particularly low for dolphins close to meanders where these habitat features temporarily block the view of the preceding river surface. This systematic bias in detectability during visual-only surveys may lead researchers to underestimate the importance of heavily meandering river reaches. Although the benefits of acoustic surveys are increasingly recognised for marine cetaceans, they have not been widely used for monitoring abundance of freshwater cetaceans due to perceived costs and technical skill requirements. We show that acoustic surveys are in fact a relatively cost-effective approach for surveying freshwater cetaceans, once it is acknowledged that methods that do not account for imperfect detectability are of limited value for monitoring.

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Section: Discussionmentioning

confidence: 99%

To See or Not to See: Investigating Detectability of Ganges River Dolphins Using a Combined Visual-Acoustic Survey

et al. 2014

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“…In our survey the A-tag was deployed closer to the survey platform, facing a noisier environment from the ship engine and propeller. Since the animals may stay away from the survey platform, documented by Li et al (2008), a lower encounter rate in the present study is anticipated. Second, the survey lines are not exactly the same between the YFDE2006 and the present cargo ship surveys.…”

Section: Discussionmentioning

confidence: 92%

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

Dong

Wang

et al. 2011

The Journal of the Acoustical Society of America

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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.

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“…This finding indicates that more porpoises can be detected further from the survey boat. Li et al (2008) also suggested that the porpoises might have been moving away from the vessel initially. Furthermore, our results indicated that they might come back toward the line after the boat crossed it.…”

Section: Discussionmentioning

confidence: 99%

Acoustic capture-recapture method for towed acoustic surveys of echolocating porpoises

Kimura

Akamatsu

Dong

et al. 2014

The Journal of the Acoustical Society of America

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Passive acoustic monitoring for cetaceans mainly employ fixed-location methods or point transect samplings; an acoustic survey from a moving platform to conduct line transects is less common. In this study, acoustic capture-recapture by combining a double-observer method with line transect sampling was performed to observe Yangtze finless porpoises. Two acoustic devices were towed with the distance between them varying 0.5 to 89.5 m. The conditional probabilities that both devices would detect the porpoises within the same time window were calculated. In a 1-s time window, it became smaller as the distance between the devices increased, approaching zero when the distance between them was more than 50 m. It was considered that the devices with less than 50 m distance detected the same signals from the same animals, which means the identical detection. When the distance between them is too great, the recapture rate is reduced and the incidence of false matching may increase. Thus, a separation distance of around 50 m between two devices in acoustic capture-recapture of Yangtze finless porpoises was recommended. Note that the performance of the double detections can change depending on the particular device used and on animal behaviors such as vocalizing interval, ship avoidance.

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Indirect Evidence of Boat Avoidance Behavior of Yangtze Finless Porpoises

Cited by 16 publications

References 1 publication

To See or Not to See: Investigating Detectability of Ganges River Dolphins Using a Combined Visual-Acoustic Survey

To See or Not to See: Investigating Detectability of Ganges River Dolphins Using a Combined Visual-Acoustic Survey

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

Acoustic capture-recapture method for towed acoustic surveys of echolocating porpoises

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