Using Static Acoustic Monitoring to Describe Echolocation Behaviour of Heaviside’s Dolphins (Cephalorhynchus heavisidii) in Namibia

Abstract

Static acoustic monitoring is a cost-effective, low-effort means of gathering large datasets on echolocation click characteristics and habitat use by odontocetes. Heaviside's dolphins (Cephalorhynchus heavisidii) were monitored using an acoustic monitoring unit, the T-POD, in July 2008 at a site of known high abundance for this species in Walvis Bay, Namibia. The T-POD successfully detected clicks from Heaviside's dolphins, and these clicks were detected in the 120 to 140 kHz frequency range. A distinct diel pattern to the hourly mean inter-click interval was observed, with higher values during daylight hours than at night, suggesting that click trains are produced at faster rates at night time. There was no apparent diel pattern in the proportion of buzz trains produced, however. A diel pattern in click activity was observed, with many more detection-positive minutes per hour recorded between dusk and dawn, and vocalization activity dropping to low levels in the middle of the day. This corresponded with visual observations made on abundance of dolphins in the study area. These results suggest that Heaviside's dolphins use this site primarily during the night. Static acoustic monitoring proved to be an effective technique for monitoring patterns of habitat use by Heaviside's dolphins.

Baltic Sea harbour porpoise populations: status and conservation needs derived from recent survey results

“…Static acoustic monitoring. Static acoustic monitoring is an effective method to survey cetaceans, especially in areas with rare registrations due to low population densities such as the harbour porpoise in the Baltic Proper (Gallus et al 2012), the vaquita Phocoena sinus in the Gulf of California, Mexico (Gerrodette et al 2011), Hector's dolphin Cephalo rhynchus hectori in New Zealand (Rayment et al 2009(Rayment et al , 2011), Heaviside's dolphin Ce pha lorhynchus heavisidii in Namibia (Leeney et al 2011), and the Ganges River dolphin Platanista gangetica in India (SasakiYama moto et al 2013). In the future, statistical methods may allow the extrapolation of acoustic de tec tions to animal abundances, which requires a detec tion function including additional information about abiotic factors, and biotic factors such as the echolocation behaviour of porpoises (Kyhn et al 2008(Kyhn et al , 2012.…”

Abundance estimate of the Amazon River dolphin (Inia geoffrensis) and the tucuxi (Sotalia fluviatilis) in southern Ucayali, Peru

“…Our results may arise from a variety of factors including a change in predator behavior as a response to prey activity patterns (Todd et al, 2009;Leeney, 2011) or movement to other areas at dawn when there is less anthropogenic activity (boat traffic, fishing), leading to fewer acoustic detections (Sasaki-Yamamoto et al, 2012). In tandem, given how acoustically dependent these species are, consideration should be given to understanding the impacts of anthropogenic sound (McKenna et al, 2016).…”

Cetacean research in the southern African subregion: a review of previous studies and current knowledge

“…The echolocation signals of the species have recently been described (Morisaka et al, 2011) and long term monitoring using moored acoustic click detectors is being developed in Namibian waters (Leeney et al, 2011) The dusky dolphin remains poorly studied in the subregion (Best and Meÿer, 2010), although data and samples from local animals have been included in broad scale morphological, taxonomic and genetic studies (Cassens et al, 2003;Cassens et al, 2005;Harlin-Cognato et al, 2007;Van Waerenbeek et al, 1995). Best and Meÿer (2010) summarised data on opportunistic sightings, diet and life history parameters from Very little dedicated field research on small cetaceans has taken place in Namibian waters, although Findlay et al (1992) provide distribution records based on sightings and strandings and Griffin and Coetzee (2005) provide a species list of small cetaceans ecorded from Namibian waters.…”

“…Access to vessel time and development of broad scale (100s of km), repeated surveys to investigate distribution, seasonality and abundance trends of these species should be prioritised. Static acoustic monitoring, provides another method with which to investigate patterns of relative abundance, distribution and seasonality (Leeney et al, 2011;Marques et al, 2009;Van Parijs et al, 2002) and techniques to estimate absolute abundance are rapidly developing (Marques et al, 2010).…”