Dear MARMAM Community, My co-authors and I are very pleased to share with you two recently published papers in *Frontiers in Marine Science* and the *African Journal of Marine Science*. The first paper provides the first abundance estimates for Heaviside's and dusky dolphins off Namibia. The second paper is a methods paper describing how we used PAM from a towed hydrophone array in combination with visual observers on line transect ship surveys to increase the detectability of Heaviside's dolphins.
*First Abundance Estimates of Heaviside’s (Cephalorhynchus heavisidii) and Dusky (Lagenorhynchus obscurus) Dolphins Off Namibia Using a Novel Visual and Acoustic Line Transect Survey* Morgan J. Martin, Tess Gridley, Jean-Paul Roux and Simon H. Elwen To link to this article: https://doi.org/10.3389/fmars.2020.555659 *Abstract:* Knowledge 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. *Towed passive acoustic monitoring complements visual survey methods for Heaviside’s dolphins Cephalorhynchus heavisidii in the Namibian Islands Marine Protected Area* Tess Gridley , Morgan J. Martin , Jeffery Slater , J-P Roux , Rene J. Swift and Simon H. Elwen To link to this article: https://doi.org/10.2989/1814232X.2020.1848925 *Abstract:* 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. Please feel free to email me for a pdf copy of either paper. Thank you for your interest in our research! Merry Christmas, Morgan J. Martin, PhD Postdoctoral researcher University of Victoria, B.C.
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