Towed passive acoustic monitoring complements visual survey methods for Heaviside's dolphins Cephalorhynchus heavisidii in the Namibian Islands Marine Protected Area

The genus Cephalorhynchus contains four dolphin species, of which three are classified as Near Threatened or Endangered and one subspecies is close to extinction. Understanding the species' abundance, distributions and habitat preferences is necessary for effective management to prevent further...

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Vydáno v:	African journal of marine science Ročník 42; číslo 4; s. 495 - 506
Hlavní autoři:	Gridley, T, Martin, MJ, Slater, J, Roux, J-P, Swift, RJ, Elwen, SH
Médium:	Journal Article
Jazyk:	angličtina
Vydáno:	Grahamstown Taylor & Francis 01.10.2020 Taylor & Francis Ltd
Témata:	Acoustic data Acoustic surveying Acoustics Africa Aquatic mammals Centroids Cephalorhynchus Cephalorhynchus heavisidii Cetacea click detection and classification Coastal ecology Coastal zone computer software Data collection Dolphins Dolphins & porpoises Echolocation Ecological distribution ecosystems encounter rate extinction Habitat preferences Habitat selection habitats Islands line-transect survey Marine mammals Marine parks Marine protected areas marine science Methods Monitoring Narrowband narrowband high-frequency clicks Offshore PAMGuard Population decline Porpoises Protected areas southwestern Atlantic Species extinction Surveys Taxonomy Threatened species Africa
ISSN:	1814-232X, 1814-2338, 1814-2338
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Popis
Shrnutí:	The genus Cephalorhynchus contains four dolphin species, of which three are classified as Near Threatened or Endangered and one subspecies is close to extinction. Understanding the species' abundance, distributions and habitat preferences is necessary for effective management to prevent further population declines. Heaviside's dolphin C. heavisidii is endemic to the Benguela ecosystem off southwest Africa, and like other Cephalorhynchus species these dolphins produce narrowband high-frequency (NBHF) echolocation clicks with a centroid frequency around 125 kHz. We conducted dedicated visual and acoustic line-transect surveys within and adjacent to the Namibian Islands Marine Protected Area in 2012-2014. Acoustic data were processed in the passive acoustic monitoring software PAMGuard, using the default porpoise click detector and classifier to identify NBHF echolocation clicks. Click detection and classification in PAMGuard included a large excess of false positives, which were easily identified by manual verification of events, and ultimately provided 52 definite detections. The acoustic methods provided data in offshore areas and during overnight periods, but were imperfect and not suitable for ecologically important shallow coastal areas. While demonstrating the utility of passive acoustic monitoring in line-transect surveys targeting Cephalorhynchus species, the study shows that both visual and acoustic methods were needed to collect data throughout the range of Heaviside's dolphin.
Bibliografie:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 14 content type line 23
ISSN:	1814-232X 1814-2338 1814-2338
DOI:	10.2989/1814232X.2020.1848925