Short-finned Pilot Research Articles

Cetacean occurrence and diversity in whale-watching waters off Mirissa, Southern Sri Lanka.

Scientific information is vital to the conservation of cetaceans and the management of whale-watching activities. The southern coastal waters of Sri Lanka are near a narrow continental shelf and biologically abundant in cetacean species. Although the occurrence of cetaceans has been investigated in certain waters of Sri Lanka, few surveys have been conducted along the southern coast. To fill this gap, we conducted boat-based surveys from January to May 2017 to investigate the occurrence, diversity, and behavior of cetaceans in the waters off Mirissa, covering a survey area of 788.9 km2 . During 55 survey days, we recorded a total of 242 cetacean sightings and identified at least 9 species (3 mysticetes and 6 odontocetes). The blue whale was the most common mysticete species (167 of 174 mysticete encounters), followed by the Omura's whale (4 of 174) and Bryde's whale (3 of 174). The spinner dolphin was the most common odontocete species (28 of 68 odontocete encounters), followed by the sperm whale (18 of 68), common bottlenose dolphin (13 of 68), short-finned pilot whale (5 of 68), melon-headed whale (2 of 68), and killer whale. Blue whales and sperm whales exhibited a clear preference for outer shelf and high slope areas, and blue whales were observed feeding along these waters. The present study provides near-baseline information on cetacean occurrence and diversity in whale-watching waters off southern Sri Lanka, and highlights the urgent need for proper management strategies for whale-watching activities.

Artisanal and Aboriginal Subsistence Whaling in Saint Vincent and the Grenadines (Eastern Caribbean): History, Catch Characteristics, and Needs for Research and Management

Whaling has been a contentious international environmental issue for decades and carries complex ecological and socioeconomic implications. In Saint Vincent and the Grenadines (SVG), a small archipelagic nation located in the Eastern Caribbean, present-day whaling traces its origin to local interaction with American-based whalers during the nineteenth and early twentieth centuries. When American whaling in the region ceased, local shore-based whaling arose to fill the niche and to exploit the remaining, though diminished, stocks of large whales, as well as stocks of small cetaceans that the American whalers had not targeted as heavily. After a period of expansion throughout the late nineteenth and early twentieth centuries, which saw shore-whaling operations established on at least 11 islands in the region, Eastern Caribbean whaling experienced a period of attrition, during which most local whaling operations ceased. Two operations, both based in SVG, continue regularly today. This paper reviews the past and present status of whaling activities in SVG from the literature and using recent data collected from 2007 to 2017 through logbook data, interview surveys, and ethnographic observations. Small cetacean captures have been documented since 1949, and at least 15 species of odontocetes have been captured (primarily delphinids). From 1949 to 2017, a total of 13,856 small cetacean captures has been recorded, including 5,896 short-finned pilot whales (Globicephala macrorhynchus), 109 killer whales (Orcinus orca), and 7,851 other small cetaceans. Small cetacean catch records are largely incomplete and total catch estimates could not be attempted. Reliable abundance estimates do not exist. Consistent records for the take of large whales are only available for the period 1986–2020, during which 45 humpback whales (Megaptera novaeangliae) and 2 Bryde’s whales (Balaenoptera edeni) were taken. Additionally, 8 sperm whale (Physeter macrocephalus) captures were reported from 1967 and 1974. We also review whaling practices, existing national policy on whaling, management techniques outside of formal policy regimes, research needs, and future management perspectives. Future monitoring and management of whaling activities in SVG are strongly needed to assess the sustainability of small cetacean exploitation.

First insights on the horizontal movements of short‐finned pilot whales in the Gulf of Mexico

AbstractThis study is the first assessment on how short‐finned pilot whales (Globicephala macrorhynchus) move within the Gulf of Mexico. In April 2018, seven adult animals were tagged using location‐only satellite transmitters in the south‐western Gulf (18°59′N and 95°19′W). When tagged, all animals were in a medium‐size aggregation that split after a week and followed two routes, indicating that the initial aggregation was consisted of at least two social units. Regardless of the route, short‐finned pilot whales moved at a low travel rate (mean = 3.4 km/hr; 50% IC: 1.5–4.8) on the south‐western continental shelf‐break, between the 500‐ and 800‐m isobaths. The oceanography and hydrographic features of the south‐western Gulf's continental shelf‐break would favour the aggregation of prey, influencing the low dispersion observed during the transmission period, as well as the co‐occurrence of several social units. However, given the relatively short period covered (up to 87 days) and the few animals tagged, the movement patterns described here could vary at longer temporal and spatial scales.

Echolocation click parameters of short-finned pilot whales (Globicephala macrorhynchus) in the wild.

Short-finned pilot whales (Globicephala macrorhynchus) are large, deep-diving predators with diverse foraging strategies, but little is known about their echolocation. To quantify the source properties of short-finned pilot whale clicks, we made 15 deployments off the coast of Tenerife of a deep-water hydrophone array consisting of seven autonomous time-synced hydrophone recorders (SoundTraps), enabling acoustic localization and quantification of click source parameters. Of 8185 recorded pilot whale clicks, 47 were classified as being recorded on-axis, with a mean peak-to-peak source level (SL) of 181 ± 7 dB re 1 μPa, a centroid frequency of 40 ± 4 kHz, and a duration of 57 ± 23 μs. A fit to a piston model yielded an estimated half-power (-3 dB) beam width of 13.7° [95% confidence interval (CI) 13.2°-14.5°] and a mean directivity index (DI) of 22.6 dB (95% CI 22.5-22.9 dB). These measured SLs and DIs are surprisingly low for a deep-diving toothed whale, suggesting we sampled the short-finned pilot whales in a context with little need for operating a long-range biosonar. The substantial spectral overlap with beaked whale clicks emitted in similar deep-water habitats implies that pilot whale clicks may constitute a common source of false detections in beaked whale passive acoustic monitoring efforts.

The Challenges of Managing Depredation and Bycatch of Toothed Whales in Pelagic Longline Fisheries: Two U.S. Case Studies

Direct interactions with fisheries are broadly recognized as the leading conservation threat to small cetaceans. In open-ocean environments, one of the primary gear types implicated in these interactions is the pelagic longline. Unlike accidental entanglement in driftnets or deliberate entrapment by purse-seines, interactions between cetaceans and longlines are often driven by attraction of the animals to feed on bait or fish secured on the gear, a behavior known as depredation. Many small and medium-sized delphinid species have learned to exploit such opportunities, leading to economic costs to fisheries and a risk of mortality to the animals from either retaliation by fishermen or hooking or entanglement in fishing gear. Two pelagic longline fisheries in the United States experience depredation and bycatch by odontocete depredators: the Hawai‘i deep-set longline fishery, which is depredated primarily by false killer whales (Pseudorca crassidens), and the Atlantic pelagic longline fishery depredated primarily by short-finned pilot whales (Globicephala macrorhynchus). These fisheries are among the most intensively documented and managed pelagic longline fisheries in the world, with high levels of observer coverage, and bycatch mitigation measures required to reduce the mortality of seabirds, sea turtles and cetaceans. Both fisheries have active, multi-stakeholder “Take Reduction Teams,” enacted under the U.S. Marine Mammal Protection Act (MMPA), that are tasked to develop measures to reduce the bycatch of cetaceans below statutory reference points. Consequently, these two Teams represent model processes within which to address depredation and bycatch, having access to detailed, high-quality data on the nature and frequency of interactions with cetaceans, meaningful stakeholder involvement, resources to test potential solutions, and the institutional will to improve outcomes. We review how mitigation strategies have been considered, developed, and implemented by both Teams and provide a critical analysis of their effectiveness in addressing these problems. Notably, in the absence of straightforward avoidance or deterrence strategies, both Teams have developed gear and handling strategies that depend critically on comprehensive observer coverage. Lessons offered from these Teams, which have implemented consensus-driven management measures under a statutory framework, provide important insights to managers and scientists addressing other depredation problems.

A Discourse on Why only Human and a Few Marine Mammal Females Are Menopausal

A fundamental question, relating to menopause that has not been convincingly answered, is this: of the thousands of known mammals on earth, why are humans and a few marine mammals the only ones whose females are menopausal? Here we provide an answer to that key question by looking at three elemental criteria that all menopausal species must fulfill: first, it has to be long-lived (average female lifespan has to be over forty years); second, it has to be a social animal, that is, it must live in groups; and third, the average female-male lifespan differential has to be at least thirty percent or more. In addition, we also found a corollary criterion for menopause: for a species’ females to be menopausal, the Encephalization Quotient (EQ) for the species has to be 2.5 or more. Though humans do not fulfill the third menopausal criterion currently, we have shown that when the menopause phenotype first became common in human ancestors, in all likelihood, that principle was conformed to. Of the multitude of mammals around, only a few species satisfy all three menopausal criteria, and hence are the only ones whose females undergo the menopause phenomenon. Many hitherto unanswered questions with respect to menopause, such as, while long and short-finned pilot whales are close to each other both genetically and physiologically, why are short-finned females menopausal while long-finned females are not, why orca females are menopausal while elephant females are not, in spite of both being long-lived, etc., can be answered on the basis of those three criteria. It is also shown that grand-mothering and mate-choice are consequences of menopause and not its cause – those mechanisms had been the explanatory bases of some previously-advanced theories trying to explain why menopause occurs in the first place. It is also shown why there was no selection pressure for males to undergo advanced-age reproductive cessation in those few menopausal species. Lastly, why the majority of divorces occur in mid-life (40s-to-60s) is explained from a menopausal perspective.

A pioneering survey of deep-diving and off-shore cetaceans in the northern South China Sea.

A pioneering boat-based survey was conducted in 2019, to gather baseline information regarding the presence, composition, relative abundance, and spatial distribution of deep-diving and off-shore cetaceans in the northern South China Sea (SCS). A total of 27 sightings comprising at least 8 cetacean species were recorded during the 13-day survey, including 5 deep-diving species (i.e. Risso's dolphin [Grampus griseus], short-finned pilot whale [Globicephala macrorhynchus], sperm whale [Physeter macrocephalus], Cuvier's beaked whale [Ziphius cavirostris], and an unidentified beaked whale [either the ginkgo-toothed beaked whale, Mesoplodon ginkgodens, or Deraniyagala's beaked whale, Mesoplodon hotaula]), as well as 3 off-shore dolphins (i.e. pantropical spotted dolphin [Stenella attenuate], striped dolphin [Stenella coeruleoalba], and Fraser's dolphin [Lagenodelphis hosei]). With the exception of pantropical spotted dolphins, all other species were sighted and recorded at sea in the northern SCS for the first time. The pantropical spotted dolphin was the most frequently sighted species, comprising 30% of the total sightings. Deep-diving cetaceans were mainly sighted in the northern Xisha Archipelago, whereas off-shore dolphins were distributed across the survey area. The pantropical spotted dolphin was observed in aggregations of more than 100 individuals and nearly all encountered species included calves; these findings suggested that the survey area functions as an important feeding and calving ground for various cetacean species. This pioneering survey provides fundamental information regarding cetacean fauna in the northern SCS and highlights the need to strengthen research and conservation efforts concerning these species.

Sebaran dan Keanekaragaman Cetacea saat Musim Timur di Perairan Tejakula, Buleleng, Bali

Cetaceans are marine mammals whose entire life is in marine and fresh waters. Cetaceans consist of whales, dolphins, and porpois. The distribution of cetaceans is a matter that shows the points of emergence of cetaceans in a waters. Diversity index is to determine the diversity of a group by looking at the number of species in a group. The waters of Tejakula Subdistrict are one of the waters in North Bali. The waters of North Bali is one of the waters which has become a migration path for several species of cetaceans. As a cetacean migration pathway, there are many occurrences of cetaceans in the northern waters of Bali. One of the most famous locations for the emergence of cetaceans in Bali is the waters of the Tejakula District, so research on cetaceans in the waters of the Tejakula Subdistrict needs to be done. This study aims to determine the distribution and diversity of cetaceans in the waters of Tejaula District. This research was conducted for 3 months, namely in the months of July, August and September 2017. Research on the distribution of cetaceans was carried out to determine the cetacean emergence points. The types of cetaceans found during the three months of the study were Stenella longirostris, Stenella attenuata, Globicephala macrorhynchus, Steno bredanensis, Lagenodelphis hosei, and Grampus griseus. The diversity of cetaceans in the waters of the Tejakula sub-district in July was 0.55, August 1.24 and September 0.9. The cetacea diversity index in the study area was divided into two, namely the area outside the reserve 1.22 and the area in the reserve 0.55.

Australian long-finned pilot whales (Globicephala melas) emit stereotypical, variable, biphonic, multi-component, and sequenced vocalisations, similar to those recorded in the northern hemisphere

While in the northern hemisphere, many studies have been conducted on the vocal repertoire of long-finned pilot whales (Globicephala melas), no such study has been conducted in the southern hemisphere. Presented here, is the first study on the vocalisations of long-finned pilot whales along the southern coast of mainland Australia. Multiple measures were taken of 2028 vocalisations recorded over five years in several locations. These vocalisations included tonal sounds with and without overtones, sounds of burst-pulse character, graded sounds, biphonations, and calls of multiple components. Vocalisations were further categorised based on spectrographic features into 18 contour classes. Altogether, vocalisations ranged from approximately 200 Hz to 25 kHz in fundamental frequency and from 0.03 s to 2.07 s in duration. These measures compared well with those from northern hemisphere pilot whales. Some call types were almost identical to northern hemisphere vocalisations, even though the geographic ranges of the two populations are far apart. Other call types were unique to Australia. Striking similarities with calls of short-finned pilot whales (Globicephala macrorhynchus) and sometimes sympatric killer whales (Orcinus orca) were also found. Theories for call convergence and divergence are discussed.

Cetacean diversity of Mauritius

There is limited information concerning the cetaceans inhabiting the coastal waters of Mauritius. This document details the sightings of cetaceans encountered during April 2008 – September 2014. Boat-based surveys were conducted throughout the year, primarily focusing on spinner and bottlenose dolphin populations that are important for the local dolphin-watching industry. More than 1246 hours over 749 days of surveys were spent searching for cetaceans. All cetaceans encountered were recorded. During 2013 and 2014, dedicated diversity surveys were conducted and 2443.6km of search effort was covered around the islands. The encounter rate was 0.025 cetacean sightings/km. Over the total study period 13 species were recorded from 1459 sightings. Species included: Megaptera novaeangliae, Stenella longirostris, Tursiops aduncus, Tursiops truncatus, Globicephala macrorhynchus, Stenella attenuata, Physeter macrocephalus, Mesoplodon densirostris, Feresa attenuata, Peponocephala electra, Grampus griseus and Ziphius cavirostris. In addition, there were strandings of Kogia sima and Ziphius cavirostris. The most common species encountered were spinner dolphins, Indo-Pacific bottlenose dolphins, humpback whales and sperm whales. As expected only humpback whales showed any seasonality in monthly encounter rates (Kruskal-Wallis H = 42.39, Hc = 54.25, p < 0.001). The overall Shannon diversity index was 0.58 (95% CI 0.57–0.60) though this ranged between 0.77 in 2009 to 0.25 in 2014. The Shannon index value for the diversity study was 0.83 (95% CI 0.74–0.91). This study demonstrates the richness of the waters around Mauritius and the importance of the area for beaked whales, migrating humpback whales and the presence of resident sperm whales.

The impact of temperature at depth on estimates of thermal habitat for short‐finned pilot whales

AbstractShort‐finned pilot whales (Globicephala macrorhynchus) experience dramatic changes in temperature during deep dives, but studies of pilot whale habitat use typically rely solely on surface temperature measurements. We quantified vertically integrated thermal habitat for short‐finned pilot whales using a novel metric, degree‐hours, developed using data from digital acoustic recording tags (DTAGs) deployed off Cape Hatteras along with interpolated temperature profiles at depth from the Met Office Hadley Centre EN4 oceanographic data set. We then compared estimates of thermal habitat calculated from surface waters with estimates of vertically integrated thermal habitat calculated using EN4 data collected along the eastern seaboard of the U.S. to understand how available thermal habitat is influenced by seasonal and spatial variability in water temperature. Estimates of vertically integrated thermal habitat were typically lower than estimates produced using surface temperatures, and the difference was greatest at intermediate latitudes and in warmer seasons, where and when there is a high degree of variability between surface and bottom temperatures. Our work highlights the importance of considering temperature at depth to accurately assess the thermal habitat of deep‐diving marine vertebrates, and presents a means of quantifying thermal habitat that will be useful for understanding the thermal ranges of these species.

Maximum entropy model: Estimating the relative suitability of cetacean habitat in the northern Savu Sea, Indonesia

AbstractAn understanding of cetacean distribution is necessary to gain insights into crucial ecological processes for species conservation management. However, cetacean habitat preference and distribution in the northern Savu Sea, Indonesia, are still poorly understood. We use maximum entropy modeling with five environmental predictors to describe habitat preference and distribution of seven cetacean species in the northern Savu Sea. Our study confirms that static predictors are the most important variables in explaining habitat preferences of seven cetacean species in the northern Savu Sea. Seasonally, each cetacean species has a different environmental preference. Globicephala macrorhynchus prefers the open nearshore areas adjacent to deep waters. Stenella attenuata is associated with nearshore habitats and higher productivity areas. Stenella longirostris prefers nearshore habitat during coastal upwelling events. Tursiops truncatus prefers nearshore sheltered habitat. Grampus griseus habitats are highly related to depth and steep gradients around the isobaths of 200–1,000 m. Feresa attenuata are associated with deep waters and cooler sea temperature. Pseudorca crassidens prefers protective bays with productive waters. This study provides important information for reviewing marine spatial plans of the northern Savu Sea, specifically on managing species fisheries interaction, optimizing surveillance, and regulating marine traffic.

CASE OF NASITREMA SP. EGGS DETECTION IN CAPTIVE SHORT-FINNED PILOT WHALE (GLOBICEPHALA MACRORHYNCHUS)

The Nasitrema sp. parasitization in the short-finned pilot whale (Globicephala macrorhynchus) was detected using intravital diagnostic methods for the first time. The material for the study was excreted content of the upper respiratory tract which was voluntarily obtained from the whale ("blow" to the Petri dish at the trainer’s command). The study was conducted in May of 2016 at the Moskvarium – Center for Oceanography and Marine Biology. Two individuals of the short-finned pilot whale were captured in Taiji Bay (Japan) in the autumn of 2014 and transferred to Russia by air in January of 2016. The animals were kept at the temporary base in the Gerasimikha village, Pushkin district, Moscow region. Ovoscopy was performed using the native smear and Mikmed-5 light microscope (LOMO) in the light field. Yellowish eggs with caps at one of the poles were found in samples from one of the pilot whales. They were identified up to the genus (Nasitrema) according to their morphology and epizootic data. The life cycle of Nasitrema has not yet been revealed; however, being a Digenea, it, probably, must be heteroxenic. Therefore, an infected pilot whale is not a danger to other individuals.

Marine mammal skin microbiotas are influenced by host phylogeny.

Skin-associated microorganisms have been shown to play a role in immune function and disease of humans, but are understudied in marine mammals, a diverse animal group that serve as sentinels of ocean health. We examined the microbiota associated with 75 epidermal samples opportunistically collected from nine species within four marine mammal families, including: Balaenopteridae (sei and fin whales), Phocidae (harbour seal), Physeteridae (sperm whales) and Delphinidae (bottlenose dolphins, pantropical spotted dolphins, rough-toothed dolphins, short-finned pilot whales and melon-headed whales). The skin was sampled from free-ranging animals in Hawai‘i (Pacific Ocean) and off the east coast of the United States (Atlantic Ocean), and the composition of the bacterial community was examined using the sequencing of partial small subunit (SSU) ribosomal RNA genes. Skin microbiotas were significantly different among host species and taxonomic families, and microbial community distance was positively correlated with mitochondrial-based host genetic divergence. The oceanic location could play a role in skin microbiota variation, but skin from species sampled in both locations is necessary to determine this influence. These data suggest that a phylosymbiotic relationship may exist between microbiota and their marine mammal hosts, potentially providing specific health and immune-related functions that contribute to the success of these animals in diverse ocean ecosystems.

Ecophysiological traits of highly mobile large marine predators inferred from nucleic acid derived indices

Nucleic acid-derived indices such as RNA/DNA ratios have been successfully applied as ecophysiological indicators to assess growth, nutritional condition and health status in marine organisms given that they provide a measure of tissue protein reserves, which is known to vary depending on changes in the environment. Yet, the use of these biochemical indices on highly mobile large predators is scarce. In this study, we tested the applicability of using nucleic acids to provide insights on the ecophysiological traits of two marine mammal species (common bottlenose dolphins and short-finned pilot whales) and explored potential related factors (species, sex, season, and residency pattern), using skin tissue (obtained from biopsy darts) of apparently healthy and adult free-ranging animals. Significantly higher RNA/DNA ratios were obtained for bottlenose dolphins (p < 0.001), and for visitor pilot whales when compared with resident pilot whales (p = 0.001). No significant changes were found between the sexes. Based on the percentile approach, the samples contain individuals in a general good condition (as the 10th percentile is not closer to the mean than the 75th percentile), suggesting that the studied region of Macaronesia may be considered an adequate habitat. The combination of this effective tool with genetic sexing and photographic-identification provided an overall picture of ecosystem health, and although with some limitations and still being a first approach, it has the applicability to be used in other top predators and ecosystems.

Post-Release Monitoring of a Stranded and Rehabilitated Short-Finned Pilot Whale (Globicephala macrorhynchus) Reveals Current-Assisted Travel

Post-Release Monitoring of a Stranded and Rehabilitated Short-Finned Pilot Whale (Globicephala macrorhynchus) Reveals Current-Assisted Travel

Marine mammals used as bait for improvised fish aggregating devices in marine waters of Ecuador, eastern tropical Pacific

Fish aggregating devices (FADs) are floating objects typically used to attract and capture pelagic fish in industrial tuna fisheries. This study documents 9 cases, involving 31 marine mammals, of incidentally captured, killed or otherwise retrieved cetaceans and pinnipeds which were used, or presumably used, as bait for improvised fish aggregation devices (IFAD) by artisanal fishers in coastal Ecuador. At least 3 species of small cetaceans were affected, including pantropical spotted dolphinStenella attenuata, short-finned pilot whaleGlobicephala macrorhynchus, pygmy killer whaleFeresa attenuataand an unidentified small delphinid, as well as South American sea lionsOtaria byroniawhich were reportedly killed on purpose for this fishing practice. A sperm whalePhyseter macrocephalusand a humpback whaleMegaptera novaeangliaewere presumably found floating at sea and opportunistically exploited as FADs. The South American sea lion represented 80.6% of marine mammals used as bait associated with FADs (25 sea lions out of 31 marine mammals), while the remaining 5 (possibly 6) cetacean species represented 19.4%. This is the first report of baited FADs in Ecuador, the extent of which is still unknown. This fishing technique has not been documented in other nations along the west coast of South America, although baiting of gillnets with marine mammal parts is common in Peru. Without fisheries management and regulation, this illegal fishing practice could rapidly expand and lead to further direct kills and conservation problems for targeted marine mammal populations in the eastern tropical Pacific. A bottom-up fisheries policy in concert with community-based conservation to ban the use of marine mammals as FAD bait is recommended.

Retrospective Study of Traumatic Intra-Interspecific Interactions in Stranded Cetaceans, Canary Islands.

Aggressive encounters involving cetacean species are widely described in the literature. However, detailed pathological studies regarding lesions produced by these encounters are scarce. From January 2000 to December 2017, 540 cetaceans stranded and were necropsied in the Canary Islands, Spain. Of them, 24 cases of eight species presented social traumatic lesions produced by cetaceans of the same or different species. All the cases presented severe multifocal vascular changes, 50% (12/24) presented fractures affecting mainly the thoracic region, 41.7% (10/24) acute tooth-rake marks, 37.5% (9/24) undigested food in the stomach, 33.3% (8/24) tracheal edema, and 12.5% (3/24) pulmonary perforation. In 10 cases with tooth-rake marks, the distance between the teeth, allowed us to further identify the aggressor species: four cases were compatible with killer whales (Orcinus orca) affecting three species [pigmy sperm whale (Kogia breviceps), Cuvier's beaked whale (Ziphius cavirostris), and short-finned pilot whale (Globicephala macrorhynchus)] and four cases compatible with common bottlenose dolphins (Tursiops truncatus) affecting two species [short-beaked common dolphin (Delphinus delphis) and Atlantic spotted dolphin (Stenella frontalis)]. We also described two cases of intraspecific interaction in stripped dolphin (Stenella coeruleoalba). Microscopically, 70.8% (17/24) of the cases presented acute degenerative myonecrosis, 66.7% (14/21) presented vacuoles in the myocardiocytes, 36.8% (7/19) pigmentary tubulonephrosis, 31.6% (6/19) cytoplasmic eosinophilic globules within hepatocytes, 21.4% (3/14) hemorrhages in the adrenal gland, and 17.3% (4/23) bronchiolar sphincter contraction. The statistical analysis revealed that deep divers, in good body condition and nearby La Gomera and Tenerife were more prone to these fatal interactions. Additionally, in this period, three animals died due to an accident during predation: a false killer whale (Pseudorca crassidens) died because of a fatal attempt of predation on a stingray, and two Risso's dolphins (Grampus griseus) died as a consequence of struggling while predating on large squids.

An autonomous hydrophone array to study the acoustic ecology of deep-water toothed whales

For vocal animals with distinctive calls, passive acoustic monitoring can be used to infer presence, distribution, and abundance provided that the calls and calling behaviour are known. Key to enabling quantitative acoustic surveys are calibrated recordings of identified species from which the source parameters of the sounds can be estimated. Obtaining such information from free-ranging aquatic animals such as toothed whales requires multi-element hydrophone arrays, the use of which is often constrained by cost, the logistical challenge of long cables, and the necessity for attachment to a boat or mooring in order to digitise and store multiple channels of high-sample rate audio data. Such challenges are compounded when collecting recordings or tracking the diving behaviour of deep-diving animals for which the array must be deployed at depth. Here we report the development of an autonomous drifting deep-water vertical passive acoustic array that uses readily available off-the-shelf components. This lightweight portable array can be deployed quickly and repeatedly to depths of up to 1000 m from a small boat. The array comprises seven ST-300 HF SoundTrap autonomous recorders equally spaced on an 84 m electrical-mechanical cable. The single-channel digital sound recordings were configured to allow for synchronisation in post-processing using an RS-485 timing signal logged by all channels every second. We outline how to assemble the array, and provide software for time-synchronising the acoustic recorders. To demonstrate the utility of the array, we present an example of short-finned pilot whale clicks localised on the deep-water (700 m) array configuration. This array method has broad applicability for the cost-effective study of source parameters, acoustic ecology, and diving behaviour of deep diving toothed whales, which are valuable not only to understand the sensory ecology of deep-diving cetaceans, but also to improve passive acoustic monitoring for conservation and management.

Cetacean Distribution and Diversity in Lakshadweep Waters, India, Using a Platform of Opportunity: October 2015 to April 2016

Prior stranding records suggest that at least 12 cetacean species occur within the Lakshadweep archipelago off the southwest coast of India. These islands consist of coral atolls and form the northern part of the undersea Chagos-Laccadive ridge. Distinct oceanographic features, seasonal monsoon cycles, and high productivity make this region a potentially rich cetacean habitat In this article, we report findings from the first systematic visual cetacean surveys, which were conducted from high-speed passenger ferries that sail between nine Lakshadweep islands. The surveys were carried out between October 2015 and April 2016 during both the northeast monsoon (October to December) and inter-monsoon (January to April) seasons. We used a line-transect survey framework to record sightings as well as group size estimates. We documented 139 sightings over 3,880 km of which 78 sightings were during systematic survey effort. Eight odontocete species were confirmed from these sightings: Stenella longirostris, S. attenuata, S. coeruleoalba, Tursiops spp., Globicephala macrorhynchus, Pseudorca crassidens, Grampus griseus, and Feresa attenuata. One Balaenoptera sp. was also encountered during this survey. S. longirostris was sighted the most often (n = 22) followed by Tursiops spp. (n = 18) and G. macrorhynchus (n = 13). We documented significantly higher sightings in the northeast monsoon season compared to the intermonsoon season. Along ferry routes, cetacean species differed significantly from each other with respect to their associations with seafloor slope gradients and distances to nearest landmass. We encountered mixed species assemblages of G. macrorhynchus with Tursiops sp. and S. attenuata with Tursiops sp. Given the confirmed high cetacean diversity and occurrence in this region, there is a need for in-depth, long-term studies on biogeography, ecology, and population status of cetaceans here.