Determinants of variability in signature whistles of the Mediterranean common bottlenose dolphin.

One of the most studied aspects of animal communication is the acoustic repertoire difference between populations of the same species. While numerous studies have investigated the variability of bottlenose dolphin whistles between populations, very few studies have focused on the signature whistles alone and the factors underlying differentiation of signature whistles are still poorly understood. Here we describe the signature whistles produced by six distinct geographical units of the common bottlenose dolphin (Tursiops truncatus) in the Mediterranean Sea and identify the main determinants of their variability. Particularly, the influence of the region (proxy of genetic distance), the geographic site, and the environmental (sea bottom-related) and demographical (population-related) conditions on the acoustic structure of signature whistles was evaluated. The study provides the first evidence that the genetic structure, which distinguishes the eastern and western Mediterranean bottlenose dolphin populations has no strong influence on the acoustic structure of their signature whistles, and that the geographical isolation between populations only partially affected whistle variability. The environmental conditions of the areas where the whistles developed and the demographic characteristics of the belonging populations strongly influenced signature whistles, in accordance with the "acoustic adaptation hypothesis" and the theory of signature whistle determination mediated by learning.

Bray-Call Sequences in the Mediterranean Common Bottlenose Dolphin (Tursiops truncatus) Acoustic Repertoire.

Acoustic sequences are commonly observed in many animal taxa. The vast vocal repertoire of common bottlenose dolphins (Tursiops truncatus) also includes sequences of multi-unit rhythmic signals called bray-call which are still poorly documented, both functionally and geographically. This study aimed to (1) describe, classify, and characterize series of bray-call recorded in two sites of the Mediterranean basin (Rome-Tyrrhenian Sea and Mazara del Vallo-Strait of Sicily) and (2) investigate for the existence of possible geographic differences. The acoustic analysis identified 13 different sequence types, only two detected in both study areas. The Sørensen-Dice index revealed a low degree of similarity between the sequence repertoire of the two common bottlenose dolphin sub-populations, with the Tyrrhenian being more diversified and complex than the Sicilian one. The acoustic parameters also showed variability between the study area. Different variants of the main acoustic elements composing the bray-call sequences were detected in the Tyrrhenian Sea only. The Markov-chain model demonstrated that the transition probability between acoustic elements is not uniform, with specific combinations of elements having a higher probability of occurrence. These new findings on common bottlenose dolphin bray-call sequences highlight the structural complexity of these vocalizations and suggest addressing future research on the context of emissions and the possible function(s) of such acoustic arrangements.

Long-Term Monitoring of Dolphin Biosonar Activity in Deep Pelagic Waters of the Mediterranean Sea.

Dolphins emit short ultrasonic pulses (clicks) to acquire information about the surrounding environment, prey and habitat features. We investigated Delphinidae activity over multiple temporal scales through the detection of their echolocation clicks, using long-term Passive Acoustic Monitoring (PAM). The Istituto Nazionale di Fisica Nucleare operates multidisciplinary seafloor observatories in a deep area of the Central Mediterranean Sea. The Ocean noise Detection Experiment collected data offshore the Gulf of Catania from January 2005 to November 2006, allowing the study of temporal patterns of dolphin activity in this deep pelagic zone for the first time. Nearly 5,500 five-minute recordings acquired over two years were examined using spectrogram analysis and through development and testing of an automatic detection algorithm. Echolocation activity of dolphins was mostly confined to nighttime and crepuscular hours, in contrast with communicative signals (whistles). Seasonal variation, with a peak number of clicks in August, was also evident, but no effect of lunar cycle was observed. Temporal trends in echolocation corresponded to environmental and trophic variability known in the deep pelagic waters of the Ionian Sea. Long-term PAM and the continued development of automatic analysis techniques are essential to advancing the study of pelagic marine mammal distribution and behaviour patterns.

Cetacean sightings and acoustic detections during a seismic survey off Nicaragua and Costa Rica, November-December 2004 / Avistamientos y detecciones acústicas de cetáceos durante un sondeo sísmico en aguas fuera de las costas de Nicaragua y Costa Rica, en Noviembre y Diciem bre 2004

AbstractAlthough the wider Eastern Tropical Pacific has been systematically surveyed during summer/fall, relatively little effort has focused on shelf and slope waters of Nicaragua and Costa Rica. Such data are useful for establishing baseline information and assessing potential changes in cetacean occurrence and distribution relative to natural (e.g., El Niño-Southern Oscillation, climate change) and anthropogenic factors. A visualacoustic survey for cetaceans occurred as part of a monitoring and mitigation program during an academic geophysical seismic study off Nicaragua and Costa Rica, during November-December 2004. Approximately 2 067 cetaceans representing at least seven species were seen in 75 groups during 373 h (3 416 km) of daytime observations from the seismic research vessel (R/V) Maurice Ewing. The humpback whale (Megaptera novaeangliae) and the pantropical spotted dolphin (Stenella attenuata) were the most frequently sighted species (30 % of all groups sighted); both were seen in shelf waters < 100 m deep and in slope waters. The bottlenose dolphin (Tursiops truncatus; 10 % of sightings) was the third most frequently sighted species and was only seen in water > 100 m deep. In addition, sightings were made of spinner dolphins (S. longirostris), short-beaked common dolphins (Delphinus delphis), Risso's dolphins (Grampus griseus), short-finned pilot whales (Globicephala macrorhynchus), and unidentified dolphins and whales. Unconfirmed sightings of a minke whale (Balaenoptera acutorostrata) and a pod of false killer whales (Pseudorca crassidens) were also recorded. An additional six groups of dolphins (50 % confirmed to species, all pantropical spotted dolphins) were made during 187 h (1 549 km) of observation effort during darkness, two of which were detected within 30 m of the vessel bow using a night vision device. A total of 217 cetacean detections occurred during 633 h of passive acoustic monitoring. A small concentration of 12 humpback whales was seen in eight groups, and two humpbacks were recorded singing in the Gulf of Fonseca on 9 December 2004. To our knowledge, such concentrations of humpback whales, particularly singing humpbacks, have not been previously reported in this specific area. In addition, a humpback mother-calf pair, likely from the Northern Hemisphere population, was seen off Northern Costa Rica on 25 November 2004. Although cetacean sighting rates were significantly different during seismic and non-seismic periods even when corrected for differential detection probability related to sea conditions, our survey results do provide information to address previous data gaps on cetacean occurrence in shelf and slope waters off the Pacific coast of Central America during late fall.

ResumenAunque el ancho Pacífico Tropical Oriental ha sido sistemáticamente sondeado durante el verano/otoño, relativamente poco esfuerzo se ha aplicado tanto en aguas de la plataforma continental como el talud de Nicaragua y Costa Rica. Tales datos son útiles para establecer una información base y evaluar los cambios potenciales en la presencia y distribución relacionada tanto a factores naturales (ej., fenómeno de El Niño, cambio climático) como a factores antropogénicos. Un sondeo visual y acústico de cetáceos fue realizado como parte de un programa de monitoreo y mitigación durante un estudio académico de geofísica (sísmica) en las afueras de las costas de Nicaragua y Costa Rica durante Noviembre y Diciembre 2004. Aproximadamente 2 067 cetáceos representantes de al menos siete especies fueron avistados en 75 grupos durante 373 h (3 416 km) de observación diurna desde el buque de prospección sísmica (R/V) Maurice Ewing. La ballena jorobada (Megaptera novaeangliae) y el delfín manchado pantropical (Stenella attenuata) fueron las especies más frecuentemente avistadas (30 % de todos los grupos avistados); ambas fueron avistadas tanto en aguas de la plataforma continental < 100 m de profundidad como en aguas del talud. El delfín nariz de botella (Tursiops truncatus; con un 10 % de los avistamientos) fue la tercera especie más avistada, solamente visto en aguas > 100 m de profundidad. Adicionalmente, se registraron avistamientos de delfines acróbatas (S. longirostris), delfines comunes de hocico corto (Delphinus delphis), calderones grises (Grampus griseus), ballenas piloto de aleta corta (Globicephala macrorhynchus) además de ballenas y delfines no identificados. También se registró un avistamiento no confirmado de una ballena de minke (Balaenoptera acutorostrata) y uno de un grupo de falsas orcas (Pseudorca crassidens). Un adicional de seis avistamientos de delfines (confirmándose en un 50 % de ellos para la especie de delfín manchado pantropical) se observaron durante 187 h (1 549 km) de esfuerzo durante lapsos de oscuridad, dos de los cuales se detectaron a 30 m de la proa de la embarcación utilizando dispositivos de visión nocturna. Un total de 217 detecciones de cetáceos ocurrieron durante 633 h de monitoreo acústico pasivo. Una pequeña concentración de 12 ballenas jorobadas fue avistada en ocho grupos, y dos jorobadas fueron registradas cantando en el Golfo de Fonseca el 9 de Diciembre 2004. Para nuestro conocimiento, tal concentración de ballenas jorobadas, particularmente jorobadas cantando, no han sido reportadas previamente en esta área específica. Adicionalmente, una pareja de jorobadas madre-cría, probablemente de la población del Hemisferio Norte, fue avistada en las afueras de la costa de Costa Rica el 25 de Noviembre 2004. A pesar de que las tasas de avistamiento fueron significativamente distintas durante los periodos sísmicos y no sísmicos, incluso siendo corregidos según la probabilidad de detecciones relacionadas a las condiciones del mar, nuestro sondeo provee información que cubre vacíos previos de datos en la presencia de cetáceos en las aguas tanto de la plataforma como del talud continental fuera de las costas del Pacífico de América Central durante el otoño tardío.

Protection of Marine Mammals.

Within the European Defense Agency (EDA), the Protection of Marine Mammals (PoMM) project, a comprehensive common marine mammal database essential for risk mitigation tools, was established. The database, built on an extensive dataset collection with the focus on areas of operational interest for European navies, consists of annual and seasonal distribution and density maps, random and systematic sightings, an encyclopedia providing knowledge on the characteristics of 126 marine mammal species, data on marine mammal protection areas, and audio information including numerous examples of various vocalizations. Special investigations on marine mammal acoustics were carried out to improve the detection and classification capabilities.

Size Distribution of Sperm Whales Acoustically Identified during Long Term Deep-Sea Monitoring in the Ionian Sea.

The sperm whale (Physeter macrocephalus) emits a typical short acoustic signal, defined as a "click", almost continuously while diving. It is produced in different time patterns to acoustically explore the environment and communicate with conspecifics. Each emitted click has a multi-pulse structure, resulting from the production of the sound within the sperm whale's head. A Stable Inter Pulse Interval (Stable IPI) can be identified among the pulses that compose a single click. Applying specific algorithms, the measurement of this interval provides useful information to assess the total length of the animal recorded. In January 2005, a cabled hydrophone array was deployed at a depth of 2,100 m in the Central Mediterranean Sea, 25 km offshore Catania (Ionian Sea). The acoustic antenna, named OνDE (Ocean noise Detection Experiment), was in operation until November 2006. OνDE provided real time acoustic data used to perform Passive Acoustic Monitoring (PAM) of cetacean sound emissions. In this work, an innovative approach was applied to automatically measure the Stable IPI of the clicks, performing a cepstrum analysis to the energy (square amplitude) of the signals. About 2,100 five-minute recordings were processed to study the size distribution of the sperm whales detected during the OνDE long term deep-sea acoustic monitoring. Stable IPIs were measured in the range between 2.1 ms and 6.4 ms. The equations of Gordon (1991) and of Growcott (2011) were used to convert the IPIs into measures of size. The results revealed that the sperm whales recorded were distributed in length from about 7.5 m to 14 m. The size category most represented was from 9 m to 12 m (adult females or juvenile males) and specimens longer than 14 m (old males) seemed to be absent.

Annual Acoustic Presence of Fin Whale (Balaenoptera physalus) Offshore Eastern Sicily, Central Mediterranean Sea.

In recent years, an increasing number of surveys have definitively confirmed the seasonal presence of fin whales (Balaenoptera physalus) in highly productive regions of the Mediterranean Sea. Despite this, very little is yet known about the routes that the species seasonally follows within the Mediterranean basin and, particularly, in the Ionian area. The present study assesses for the first time fin whale acoustic presence offshore Eastern Sicily (Ionian Sea), throughout the processing of about 10 months of continuous acoustic monitoring. The recording of fin whale vocalizations was made possible by the cabled deep-sea multidisciplinary observatory, "NEMO-SN1", deployed 25 km off the Catania harbor at a depth of about 2,100 meters. NEMO-SN1 is an operational node of the European Multidisciplinary Seafloor and water-column Observatory (EMSO) Research Infrastructure. The observatory was equipped with a low-frequency hydrophone (bandwidth: 0.05 Hz-1 kHz, sampling rate: 2 kHz) which continuously acquired data from July 2012 to May 2013. About 7,200 hours of acoustic data were analyzed by means of spectrogram display. Calls with the typical structure and patterns associated to the Mediterranean fin whale population were identified and monitored in the area for the first time. Furthermore, a background noise analysis within the fin whale communication frequency band (17.9-22.5 Hz) was conducted to investigate possible detection-masking effects. The study confirms the hypothesis that fin whales are present in the Ionian Sea throughout all seasons, with peaks in call detection rate during spring and summer months. The analysis also demonstrates that calls were more frequently detected in low background noise conditions. Further analysis will be performed to understand whether observed levels of noise limit the acoustic detection of the fin whales vocalizations, or whether the animals vocalize less in the presence of high background noise.

Cetacean strandings in Italy: an unusual mortality event along the Tyrrhenian Sea coast in 2013.

An unusual mortality event involving cetaceans, mainly striped dolphins Stenella coeruleoalba (Meyen, 1833), occurred along the Tyrrhenian Sea coast of Italy during the first 3 mo of 2013. Based on post-mortem analyses carried out according to body condition on 66 dolphins (54% of stranded animals), several hypotheses to explain the causes of this mortality event were proposed. Although no definitive conclusions can be drawn, dolphin morbillivirus was deemed the most likely cause, although other infectious agents (including Photobacterium damselae damselae and herpesvirus) or environmental factors may also have contributed to this recent mortality event.

Sometimes sperm whales (Physeter macrocephalus) cannot find their way back to the high seas: a multidisciplinary study on a mass stranding.

BACKGROUND: Mass strandings of sperm whales (Physeter macrocephalus) remain peculiar and rather unexplained events, which rarely occur in the Mediterranean Sea. Solar cycles and related changes in the geomagnetic field, variations in water temperature and weather conditions, coast geographical features and human activities have been proposed as possible causes. In December 2009, a pod of seven male sperm whales stranded along the Adriatic coast of Southern Italy. This is the sixth instance from 1555 in this basin. METHODOLOGY/PRINCIPAL FINDINGS: Complete necropsies were performed on three whales whose bodies were in good condition, carrying out on sampled tissues histopathology, virology, bacteriology, parasitology, and screening of veins looking for gas emboli. Furthermore, samples for age determination, genetic studies, gastric content evaluation, stable isotopes and toxicology were taken from all the seven specimens. The animals were part of the same group and determined by genetic and photo-identification to be part of the Mediterranean population. Causes of death did not include biological agents, or the "gas and fat embolic syndrome", associated with direct sonar exposure. Environmental pollutant tissue concentrations were relatively high, in particular organochlorinated xenobiotics. Gastric content and morphologic tissue examinations showed a prolonged starvation, which likely caused, at its turn, the mobilization of lipophilic contaminants from the adipose tissue. Chemical compounds subsequently entered the blood circulation and may have impaired immune and nervous functions. CONCLUSIONS/SIGNIFICANCE: A multi-factorial cause underlying this sperm whales' mass stranding is proposed herein based upon the results of postmortem investigations as well as of the detailed analyses of the geographical and historical background. The seven sperm whales took the same "wrong way" into the Adriatic Sea, a potentially dangerous trap for Mediterranean sperm whales. Seismic surveys should be also regarded as potential co-factors, even if no evidence of direct impact has been detected.