Injury and subsequent healing of a propeller strike injury to a heaviside’s dolphin (Cephalorhynchus heavisidii)

No abstract available

Heaviside's dolphins (Cephalorhynchus heavisidii) relax acoustic crypsis to increase communication range

Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Proceedings of the Royal Society B. Biological Sciences 285 (2018): 20181178, doi:10.1098/rspb.2018.1178.The costs of predation may exert significant pressure on the mode of communication used by an animal, and many species balance the benefits of communication (e.g. mate attraction) against the potential risk of predation. Four groups of toothed whales have independently evolved narrowband high-frequency (NBHF) echolocation signals. These signals help NBHF species avoid predation through acoustic crypsis by echolocating and communicating at frequencies inaudible to predators such as mammal-eating killer whales. Heaviside’s dolphins (Cephalorhynchus heavisidii) are thought to exclusively produce NBHF echolocation clicks with a centroid frequency around 125 kHz and little to no energy below 100 kHz. To test this, we recorded wild Heaviside’s dolphins in a sheltered bay in Namibia. We demonstrate that Heaviside’s dolphins produce a second type of click with lower frequency and broader bandwidth in a frequency range that is audible to killer whales. These clicks are used in burst-pulses and occasional click series but not foraging buzzes. We evaluate three different hypotheses and conclude that the most likely benefit of these clicks is to decrease transmission directivity and increase conspecific communication range. The expected increase in active space depends on background noise but ranges from 2.5 (Wenz Sea State 6) to 5 times (Wenz Sea State 1) the active space of NBHF signals. This dual click strategy therefore allows these social dolphins to maintain acoustic crypsis during navigation and foraging, and to selectively relax their crypsis to facilitate communication with conspecifics.This research was supported by a Fulbright U.S. Research Fellowship, the National Geographic Society’s Emerging Explorers Grant in conjunction with the Waitt Foundation (38115) and the University of Pretoria’s Zoology Department. TG was funded by the Claude Leon Foundation, and SE was funded by the South African National Research Foundation. FHJ acknowledges funding from the Office of Naval Research (N00014-1410410) and an AIAS-COFUND fellowship from Aarhus Institute of Advanced Studies

Heaviside's dolphins (Cephalorhynchus heavisidii) relax acoustic crypsis to increase communication range

The costs of predation may exert significant pressure on the mode of communication used by an animal, and many species balance the benefits of communication (e.g. mate attraction) against the potential risk of predation. Four groups of toothed whales have independently evolved narrowband high-frequency (NBHF) echolocation signals. These signals help NBHF species avoid predation through acoustic crypsis by echolocating and communicating at frequencies inaudible to predators such as mammal-eating killer whales. Heaviside's dolphins (Cephalorhynchus heavisidii) are thought to exclusively produce NBHF echolocation clicks with a centroid frequency around 125 kHz and little to no energy below 100 kHz. To test this, we recorded wild Heaviside's dolphins in a sheltered bay in Namibia. We demonstrate that Heaviside's dolphins produce a second type of click with lower frequency and broader bandwidth in a frequency range that is audible to killer whales. These clicks are used in burst-pulses and occasional click series but not foraging buzzes. We evaluate three different hypotheses and conclude that the most likely benefit of these clicks is to decrease transmission directivity and increase conspecific communication range. The expected increase in active space depends on background noise but ranges from 2.5 (Wenz Sea State 6) to 5 times (Wenz Sea State 1) the active space of NBHF signals. This dual click strategy therefore allows these social dolphins to maintain acoustic crypsis during navigation and foraging, and to selectively relax their crypsis to facilitate communication with conspecifics.Data Supplement: Martin et al. 2018 Supplementary Methods from Heaviside's dolphins (Cephalorhynchus heavisidii) relax acoustic crypsis to increase communication range - Supplementary Methods include detail on the statistical analyses conducted for classifying the pulsed signal types of Heaviside's dolphins. Also, these methods contain the relevant information, steps and figures used in the acoustic modelling of the detection range and active space of a NBHF click compared to a lower-frequency burst-pulse click.Data Supplement: Martin et al. 2018 Appendix S1 from Heaviside's dolphins (Cephalorhynchus heavisidii) relax acoustic crypsis to increase communication range - Appendix S1 contains the parameter measurements for all measured Heaviside's dolphin pulsed signals.A Fulbright U.S. Research Fellowship, the National Geographic Society's Emerging Explorers Grant in conjunction with the Waitt Foundation (38115) and the University of Pretoria's Zoology Department. T.G. was funded by the Claude Leon Foundation, and S.H.E. was funded by the South African National Research Foundation. F.H.J. acknowledges funding from the Office of Naval Research (N00014-1410410) and an AIAS-COFUND fellowship from Aarhus Institute of Advanced Studies.http://rspb.royalsocietypublishing.org2019-07-25hj2018Mammal Research InstituteZoology and Entomolog

Pygmy right whale Caperea marginata records from Namibia

All known records of pygmy right whales Caperea marginata in Namibia since 1978 are summarised for the first time, including 12 strandings (live and recently dead animals) and skeletal remains from at least eight more individuals. The majority of strandings and remains were located in the Walvis Bay region, where the coastal topography of the bay and lagoon may be a primary cause for the relatively high incidence of strandings in this area. Strandings appear to occur only during the austral summer, between November and March. All but two of the records for which age is available were juveniles, suggesting that the area offshore of Walvis Bay may function as a seasonal nursery ground and that the inexperience of younger animals may cause them to become ‘entrapped’ in the bay. These data contribute substantially to the limited information on pygmy right whale distribution worldwide and the cetacean fauna of Namibia.http://www.tandfonline.com/loi/tams20hb201

Echolocation click parameters and biosonar behaviour of the dwarf sperm whale (Kogia sima)

PhD and fieldwork funding were provided by the Danmarks Grundforskningsfond (27125 to P.T.M.), the Oticon Fonden (18-0340 to C.E.M.) the Dansk Akustisk Selskab (to C.E.M.), the South Africa National Research Foundation (research career advancement fellowship to S.E.) and the Claude Leon Foundation (postdoctoral fellowship to T.G.).Dwarf sperm whales (Kogia sima) are small toothed whales that produce narrow-band high-frequency (NBHF) echolocation clicks. Such NBHF clicks, subject to high levels of acoustic absorption, are usually produced by small, shallow-diving odontocetes, such as porpoises, in keeping with their short-range echolocation and fast click rates. Here, we sought to address the problem of how the little-studied and deep-diving Kogia can hunt with NBHF clicks in the deep sea. Specifically, we tested the hypotheses that Kogia produce NBHF clicks with longer inter-click intervals (ICIs), higher directionality and higher source levels (SLs) compared with other NBHF species. We did this by deploying an autonomous deep-water vertical hydrophone array in the Bahamas, where no other NBHF species are present, and by taking opportunistic recordings of a close-range Kogia sima in a South African harbour. Parameters from on-axis clicks (n=46) in the deep revealed very narrow-band clicks (root mean squared bandwidth, BWRMS, of 3±1 kHz), with SLs of up to 197 dB re. 1 µPa peak-to-peak (μPapp) at 1 m, and a half-power beamwidth of 8.8 deg. Their ICIs (mode of 245 ms) were much longer than those of porpoises (<100 ms), suggesting an inspection range that is longer than detection ranges of single prey, perhaps to facilitate auditory streaming of a complex echo scene. On-axis clicks in the shallow harbour (n=870) had ICIs and SLs in keeping with source parameters of other NBHF cetaceans. Thus, in the deep, dwarf sperm whales use a directional, but short-range echolocation system with moderate SLs, suggesting a reliable mesopelagic prey habitat.Publisher PDFPeer reviewe

Transit station or destination? Attendance patterns, movements, and abundance estimate of humpback whales off west South Africa from photographic and genotypic matching

Humpback whales found off west South Africa (WSA) are known to display an atypical migration that may include temporary residency and feeding during spring and summer. At a regional scale there is uncertainty about how these whales relate to the greater West African Breeding Stock B as a whole, with evidence both for and against its division into two sub-stocks. A database containing sighting information of humpback whales intercepted by boat in the WSA region from 1983 to 2008 was compiled. It included a total of 1,820 identification images of ventral tail flukes and lateral views of dorsal fins. After systematic within- and between-year matching of images of usable quality, it yielded 154 different individuals identified by tail flukes (TF), 230 by left dorsal fins (LDF), and 237 by right dorsal fins (RDF). Microsatellite (MS) matching of 216 skin biopsies yielded 156 individuals. By linking all possible sightings of the same individuals using all available identification features, the periodicity and seasonality of 281 individual whales were examined. Sixty whales were resighted on different days of which 44 were between different calendar years. The most resightings for one individual was 11 times, seen in six different years, while the longest interval between first and last sightings was about 18 years. A resighting rate of 15.6% of whales at intervals of a year or more indicates long-term fidelity to the region. Shorter intervals of 1 – 6 months between sequential sightings in the same year may suggest temporary residency. The TF image collection from WSA was compared to TF collections from four other regions, namely Gabon, Cabinda (Angola), Namibia and the Antarctic Humpback Whale Catalogue (AHWC). Three matches were detected were between WSA (in late spring or summer) and Gabon (in winter), confirming direct movement between these regions. The capture-recapture data of four different identification features (TF, RDF, LDF and MS) from six successive subsets of data from periods with the highest collection effort (2001 – 2007), were used to calculate the number of whales that utilise the region, using both closed and open-population models. Since dorsal fins have never been used to estimate abundance for humpback whales, the different identification features were evaluated for potential biases. This revealed 9 – 14% incidence of missed matches (false negatives) when using dorsal fins that will result in an overestimate, while variation in individual fluke-up behaviour may lower estimates due to heterogeneity of individual capture probability, by as much as 57-69%. Taking into consideration the small dataset and low number of recaptures, the most consistent and precise results were obtained from a fully time-dependent version of the Jolly-Seber open-population model, with annual survival fixed at 0.96, using the MS dataset. This suggests that the WSA feeding assemblage during the months of spring and summer of the study period numbered about 500. The relationship of these whales to those (perhaps strictly migratory) that may occur here in other seasons of the year, and their links to possible migratory routes and other feeding or breeding areas remain uncertain.National Research Foundation (NRF), South Africa, under Grant Number 2047517. Earthwatch Institute (funding), The Mazda Wildlife Fund (through the provision of a field vehicle), SASOL (through the donation of two four-stroke engines), PADI Project AWARE (UK) (funding), the South African Navy (access to the shore-based look-out), the Military Academy, University of Stellenbosch (accommodation) and Iziko South African Museum (office space and support). JB gratefully received financial support in the form of bursaries from the NRF, the Society for Marine Mammalogy, University of Pretoria, and the Wildlife Society of South Africa (Charles Astley Maberley Memorial bursary). The Namibian Dolphin Project is supported by NACOMA (Namibian Coastal Conservation and Management Project), the Nedbank Go Green Fund, Mohammed bin Zayed Species Conservation Fund, the British Ecological Society, the Rufford Small Grants Foundation and the Namibia Nature Foundation. JB and TJQC received funding from the International Whaling Commission (IWC) to conduct between-region matching.http://www.tandfonline.com/loi/tams20nf201

Injury and Subsequent Healing of a Propeller Strike Injury to a Heaviside's Dolphin (<I>Cephalorhynchus heavisidii</I>)

No abstract available

Interactions between leatherback turtles and killer whales in Namibian waters, including possible predation

Killer whales and leatherback turtles are infrequently sighted in the coastal waters of southern Africa. Year round observations in Walvis Bay, Namibia of killer whales (2003–2010) by multiple marine tour operators and opportunistic seasonal observations of leatherback turtles made during a cetacean research project in the area (2008–2010) have been collated. Visits to coastal waters by killer whales (n = 16) are sporadic and unpredictable but are slightly higher (n = 11) between late winter (August) and late summer (March). Leatherback turtles were only seen in the warmer periods of summer months (February–March) when the surface waters exceeded 15°C. Two interactions (one harassment and one probably predation) between killer whales and leatherback turtles have been recorded in Walvis Bay. This is the first report of killer whales eating leatherback turtles in the South Atlantic. These observations are noteworthy due to the low frequency of encounters of both species in the area, suggesting predation of turtles may be relatively common. Knowledge of the diet of killer whales is valuable due to the importance of dietary specialization in definition of ecotypes of the species.The Namibian Dolphin Project is funded by the Nedbank Go Green Fund, NACOMA (Namibian Coastal Conservation and Management Project), the Mohammed bin Zayed Species Conservation Fund, the British Ecological Society and the Rufford Small Grants Foundation.http://www.sawma.co.za/nf201

Using static acoustic monitoring to describe echolocation behaviour of Heaviside’s dolphins (Cephalorhynchus heavisidii) in Namibia

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

Data from: Heaviside's dolphins (Cephalorhynchus heavisidii) relax acoustic crypsis to increase communication range

The costs of predation may exert significant pressure on the mode of communication used by an animal, and many species balance the benefits of communication (e.g. mate attraction) against the potential risk of predation. Four groups of toothed whales have independently evolved narrowband high-frequency (NBHF) echolocation signals. These signals help NBHF species avoid predation through acoustic crypsis by echolocating and communicating at frequencies inaudible to predators such as mammal-eating killer whales. Heaviside’s dolphins (Cephalorhynchus heavisidii) are thought to exclusively produce NBHF echolocation clicks with a centroid frequency around 125 kHz and little to no energy below 100 kHz. To test this, we recorded wild Heaviside’s dolphins in a sheltered bay in Namibia. We demonstrate that Heaviside’s dolphins produce a second type of click with lower frequency and broader bandwidth in a frequency range that is audible to killer whales. These clicks are used in burst-pulses and occasional click series but not foraging buzzes. We evaluate three different hypotheses and conclude that the most likely benefit of these clicks is to decrease transmission directivity and increase conspecific communication range. The expected increase in active space depends on background noise but ranges from 2.5 (Wenz Sea State 6) to 5 times (Wenz Sea State 1) the active space of NBHF signals. This dual click strategy therefore allows these social dolphins to maintain acoustic crypsis during navigation and foraging, and to selectively relax their crypsis to facilitate communication with conspecifics