First abundance estimates of Heaviside's (Cephalorhynchus heavisidii) and Dusky (Lagenorhynchus obscurus) dolphins off Namibia using a novel visual and acoustic line transect survey

dc.contributor.authorMartin, Morgan Jennifer
dc.contributor.authorGridley, Tess
dc.contributor.authorRoux, Jean-Paul
dc.contributor.authorElwen, Simon Harvey
dc.date.accessioned2020-11-16T14:12:23Z
dc.date.available2020-11-16T14:12:23Z
dc.date.issued2020-09
dc.description.abstractKnowledge of a population’s abundance is of primary importance for conservation management. However, robust estimates of abundance are often difficult to obtain, especially for cetaceans which spend most of their lives submerged. Cetacean abundance is commonly estimated using aerial or vessel-based line transect surveys and distance sampling methods. During 2012–2014, the first line transect surveys to estimate cetacean abundance were conducted in Namibian waters. Surveys took place in the Namibian Islands’ Marine Protected Area (NIMPA), a large MPA located along the southern Namibian coastline. A combined visual and acoustic double-platform survey configuration was used to investigate the factors affecting detectability of the endemic Heaviside’s dolphin (Cephalorhynchus heavisidii) and dusky dolphin (Lagenorhynchus obscurus obscurus). The present analysis estimates the probability of detection on the transect line (g(0)) for these two species and generates density and abundance estimates which incorporate a correction for both animals missed on the transect line and attractive responsive movement. The average annual baseline density and abundance estimates for Heaviside’s dolphins in the NIMPA region during 2012–2014 were 0.08 individuals/km2 (CV = 28.6%, 95% CI = 0.04–0.15 individuals/km2 ) and 1594 individuals (CV = 28.6%, 95% CI = 776–3275), respectively. The average annual baseline density and abundance estimates for dusky dolphins in the NIMPA region during 2012– 2014 were 0.16 individuals/km2 (CV = 26.2%, 95% CI = 0.10–0.28 individuals/km2 ) and 3493 individuals (CV = 26.2%, 95% CI: 2015–6052), respectively. A discussion on the distribution of Heaviside’s and dusky dolphins is provided for this region where such information is urgently needed. Based on existing knowledge of the species and area, these estimates are regarded as reasonable. They indicate moderate sized populations of animals within the NIMPA and provide an important first baseline on which future estimates can build.en_ZA
dc.description.departmentMammal Research Instituteen_ZA
dc.description.departmentZoology and Entomologyen_ZA
dc.description.librarianpm2020en_ZA
dc.description.sponsorshipThe Namibian Ministry of Fisheries and Marine Resources (MFMR); Nedbank Go Green Fund; Rufford Small Grants Foundation; SCOR Visiting Scholar Fund; Fulbright U.S. Research Fellowship; National Geographic Society Explorers Grant in conjunction with the Waitt Foundation; University of Pretoria’s Zoology Department; Stellenbosch University.en_ZA
dc.description.urihttp://frontiersin.org/Marine_Scienceen_ZA
dc.identifier.citationMartin MJ, Gridley T, Roux J-P and Elwen SH (2020) First Abundance Estimates of Heaviside’s (Cephalorhynchus heavisidii) and Dusky (Lagenorhynchus obscurus) Dolphins Off Namibia Using a Novel Visual and Acoustic Line Transect Survey. Frontiers in Marine Science 7:555659. doi: 10.3389/fmars.2020.555659.en_ZA
dc.identifier.issn2296-7745 (online)
dc.identifier.other10.3389/fmars.2020.555659
dc.identifier.urihttp://hdl.handle.net/2263/77031
dc.language.isoenen_ZA
dc.publisherFrontiers Mediaen_ZA
dc.rights© 2020 Martin, Gridley, Roux and Elwen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).en_ZA
dc.subjectAbundanceen_ZA
dc.subjectConservationen_ZA
dc.subjectDouble-platform line transect surveyen_ZA
dc.subjectMarine protected area (MPA)en_ZA
dc.subjectNear threatened speciesen_ZA
dc.subjectPassive acoustic monitoringen_ZA
dc.subjectSmall cetaceanen_ZA
dc.subjectHeaviside's dolphin (Cephalorhynchus heavisidii)en_ZA
dc.subjectDusky dolphin (Lagenorhynchus obscurus)en_ZA
dc.subjectMark–recapture distance sampling (MRDS)en_ZA
dc.subjectNamibian Islands’ marine protected area (NIMPA)en_ZA
dc.titleFirst abundance estimates of Heaviside's (Cephalorhynchus heavisidii) and Dusky (Lagenorhynchus obscurus) dolphins off Namibia using a novel visual and acoustic line transect surveyen_ZA
dc.typeArticleen_ZA

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