Manuel Castellote

The beluga whale produces two pulses to form its sonar signal

Odontocete cetaceans use biosonar clicks to acoustically probe their aquatic environment with an aptitude unmatched by man-made sonar. A cornerstone of this ability is their use of short, broadband pulses produced in the region of the upper nasal passages. Here we provide empirical evidence that a beluga whale (Delphinapterus leucas) uses two signal generators simultaneously when echolocating. We show that the pulses of the two generators are combined as they are transmitted through the melon to produce a single echolocation click emitted from the front of the animal. Generating two pulses probably offers the beluga the ability to control the energy and frequency distribution of the emitted click and may allow it to acoustically steer its echolocation beam.

Gray whale ( Eschrichtius robustus ) in the Mediterranean Sea: anomalous event or early sign of climate-driven distribution change?

On 8 May 2010, a gray whale was sighted off the Israeli Mediterranean shore and twenty-two days later, the same individual was sighted in Spanish Mediterranean waters. Since gray whales were last recorded in the North Atlantic in the 1700s, these sightings prompted much speculation about this whales population origin. Here, we consider three hypotheses for the origin of this individual: (1) it represents a vagrant individual from the larger extant population of gray whales found in the eastern North Pacific; (2) it represents a vagrant individual from the smaller extant population found in the western North Pacific; or (3) it represents an individual from the previously thought extinct North Atlantic population. We believe that the first is the most likely, based on current population sizes, on known summer distributions, on the extent of cetacean monitoring in the North Atlantic and on the results of a performed route analysis. While it is difficult to draw conclusions from such singular events, the occurrence of this individual in the Mediterranean coincides with a shrinking of Arctic Sea ice due to climate change and suggests that climate change may allow gray whales to re-colonize the North Atlantic as ice and temperature barriers to mixing between northern North Atlantic and North Pacific biomes are reduced. Such mixing, if it were to become widespread, would have implications for many aspects of the marine conservation and ecology of these two regions.

Seasonal migrations of North Atlantic minke whales: novel insights from large-scale passive acoustic monitoring networks

BackgroundLittle is known about migration patterns and seasonal distribution away from coastal summer feeding habitats of many pelagic baleen whales. Recently, large-scale passive acoustic monitoring networks have become available to explore migration patterns and identify critical habitats of these species. North Atlantic minke whales (Balaenoptera acutorostrata) perform seasonal migrations between high latitude summer feeding and low latitude winter breeding grounds. While the distribution and abundance of the species has been studied across their summer range, data on migration and winter habitat are virtually missing. Acoustic recordings, from 16 different sites from across the North Atlantic, were analyzed to examine the seasonal and geographic variation in minke whale pulse train occurrence, infer information about migration routes and timing, and to identify possible winter habitats.ResultsAcoustic detections show that minke whales leave their winter grounds south of 30° N from March through early April. On their southward migration in autumn, minke whales leave waters north of 40° N from mid-October through early November. In the western North Atlantic spring migrants appear to track the warmer waters of the Gulf Stream along the continental shelf, while whales travel farther offshore in autumn. Abundant detections were found off the southeastern US and the Caribbean during winter. Minke whale pulse trains showed evidence of geographic variation, with longer pulse trains recorded south of 40° N. Very few pulse trains were recorded during summer in any of the datasets.ConclusionThis study highlights the feasibility of using acoustic monitoring networks to explore migration patterns of pelagic marine mammals. Results confirm the presence of minke whales off the southeastern US and the Caribbean during winter months. The absence of pulse train detections during summer suggests either that minke whales switch their vocal behaviour at this time of year, are absent from available recording sites or that variation in signal structure influenced automated detection. Alternatively, if pulse trains are produced in a reproductive context by males, these data may indicate their absence from the selected recording sites. Evidence of geographic variation in pulse train duration suggests different behavioural functions or use of these calls at different latitudes.

Baseline hearing abilities and variability in wild beluga whales (Delphinapterus leucas)

While hearing is the primary sensory modality for odontocetes, there are few data addressing variation within a natural population. This work describes the hearing ranges (4–150 kHz) and sensitivities of seven apparently healthy, wild beluga whales (Delphinapterus leucas) during a population health assessment project that captured and released belugas in Bristol Bay, Alaska. The baseline hearing abilities and subsequent variations were addressed. Hearing was measured using auditory evoked potentials (AEPs). All audiograms showed a typical cetacean U-shape; substantial variation (>30 dB) was found between most and least sensitive thresholds. All animals heard well, up to at least 128 kHz. Two heard up to 150 kHz. Lowest auditory thresholds (35–45 dB) were identified in the range 45–80 kHz. Greatest differences in hearing abilities occurred at both the high end of the auditory range and at frequencies of maximum sensitivity. In general, wild beluga hearing was quite sensitive. Hearing abilities were similar to those of belugas measured in zoological settings, reinforcing the comparative importance of both settings. The relative degree of variability across the wild belugas suggests that audiograms from multiple individuals are needed to properly describe the maximum sensitivity and population variance for odontocetes. Hearing measures were easily incorporated into field-based settings. This detailed examination of hearing abilities in wild Bristol Bay belugas provides a basis for a better understanding of the potential impact of anthropogenic noise on a noise-sensitive species. Such information may help design noise-limiting mitigation measures that could be applied to areas heavily influenced and inhabited by endangered belugas.

Monitoring white whales (Delphinapterus leucas) with echolocation loggers

Monitoring programmes for white whales (Delphinapterus leucas) have been called for repeatedly in recent years because this species is likely to be negatively impacted by climate change, but also because such a broadly dispersed, high trophic feeder can serve as an effective ecosystem sentinel. Arctic ecosystems are difficult to monitor because of the extensive winter ice coverage and extreme environmental conditions in addition to low human population densities. However, passive acoustic monitoring has proved to be a reliable method to remotely survey the presence of some marine mammals in the Arctic. In this study, we evaluate the potential use of echolocation loggers (T-POD and C-POD, Chelonia Ltd.) for remote monitoring of white whales. Captive experiments and open water surveys in three arctic/subarctic habitats (ice-noise-dominated environment, ice-free environment and low-turbidity waters) were used to document detection performance and to explore the use of logger angle and inter-click interval data to look at activity patterns and tidal influences on space use. When acoustic results were compared to concurrent visual observations, echolocation detection was only attributed to periods of white whale presence near the recorder deployment sites. Both T-PODs and C-PODs effectively detected echolocation, even under noisy ice. Diel and tidal behavioural patterns were identified. Acoustically identified movement patterns between sites were visually confirmed. This study demonstrates the feasibility of monitoring white whales using echolocation loggers and describes some important features of their behaviour as examples of the potential application of this passive acoustic monitoring method in Arctic and subarctic regions.

Beluga whale (Delphinapterus leucas) vocalizations and call classification from the eastern Beaufort Sea population

Beluga whales, Delphinapterus leucas, have a graded call system; call types exist on a continuum making classification challenging. A description of vocalizations from the eastern Beaufort Sea beluga population during its spring migration are presented here, using both a non-parametric classification tree analysis (CART), and a Random Forest analysis. Twelve frequency and duration measurements were made on 1019 calls recorded over 14 days off Icy Cape, Alaska, resulting in 34 identifiable call types with 83% agreement in classification for both CART and Random Forest analyses. This high level of agreement in classification, with an initial subjective classification of calls into 36 categories, demonstrates that the methods applied here provide a quantitative analysis of a graded call dataset. Further, as calls cannot be attributed to individuals using single sensor passive acoustic monitoring efforts, these methods provide a comprehensive analysis of data where the influence of pseudo-replication of calls from individuals is unknown. This study is the first to describe the vocal repertoire of a beluga population using a robust and repeatable methodology. A baseline eastern Beaufort Sea beluga population repertoire is presented here, against which the call repertoire of other seasonally sympatric Alaskan beluga populations can be compared.

Passive acoustic monitoring of Cook Inlet beluga whales (Delphinapterus leucas)

The endangered beluga whale (Delphinapterus leucas) population in Cook Inlet, AK faces threats from a variety of anthropogenic factors, including coastal development, oil and gas exploration, vessel traffic, and military activities. To address existing gaps in understanding about the occurrence of belugas in Cook Inlet, a project was developed to use passive acoustic monitoring to document the year-round distribution of belugas, as well as killer whales (Orcinus orca), which prey on belugas. Beginning in June 2009, ten moorings were deployed throughout the Inlet and refurbished every two to eight months. Despite challenging conditions consisting of strong tidal currents carrying debris and seasonal ice cover, 83% of mooring deployments were successfully recovered. Noise from water flow, vessel traffic, and/or industrial activities was present at several sites, potentially masking some signals. However, belugas were successfully detected at multiple locations. Detections were relatively common in the upper inlet and less common or absent at middle and lower inlet locations. Killer whale signals were also recorded. Some seasonal variability in the occurrence of both belugas and killer whales was evident.

Dispersal of North Atlantic fin whales (Balaenoptera physalus) into the Mediterranean Sea and exchange between populations: Response to Giménez et al., Rapid Commun. Mass Spectrom. 2013, 27, 1801–1806

The earliest suggestions of a seasonal entrance of North Atlantic fin whales into the Mediterranean basin date back to the 19th century, and further supporting studies were published throughout the twentieth century. Despite these numerous reports, most of the recent literature on the distribution of the Mediterraneanfinwhale subpopulationhas assumedawestward seasonal migration of Mediterranean whales extending to the Strait of Gibraltar to feed in the northeastern North Atlantic Ocean, ignoring the hypothesis of an eastward influx from the North Atlantic as proposed in earlier studies. Castellote et al. (2012) revisited this subject and suggested that a seasonal entrance of North Atlantic fin whales into the Mediterranean basin was the best explanation for their acoustic results. Furthermore, this explanation was more consistent with recent results from stable isotope studies, visual observations and satellite telemetry of finwhales in theMediterranean basin, while also agreeing with current genetic knowledge. In their recent paper published in this journal, Giménez et al. (2013) describe stable isotope results from baleen plate tissue from five fin whales from the northeast Atlantic and compare them with Mediterranean results from Bentaleb et al. (2011). The authors conclude that North Atlantic whales penetrate into theMediterranean basin up to the northernmost latitudes of the region and that the border between the two putative subpopulations may not be as definite as previous acoustic investigations suggested. However, the authors have ignored or misinterpreted the acoustic results presented by Castellote et al. (2012) prompting the submission of this letter. In particular, we disagree with the following points:

Temporal peaks in beluga whale (Delphinapterus leucas) acoustic detections in the northern Bering, northeastern Chukchi, and western Beaufort Seas: 2010–2011

Two populations of beluga whales (Delphinapterus leucas) migrate annually between their summering grounds in the eastern Chukchi and eastern Beaufort Seas, and overwintering areas in the Bering Sea. To contribute to the understanding of migratory streams of this highly vocal species, we investigated temporal peaks in acoustic detections from 4-year-long (2010–2011) recorders located in the northeastern Chukchi (inshore and offshore), western Beaufort, and northern Bering Seas. Beluga calls were detected throughout summer (July–August) in the western Beaufort; other studies suggest these animals are likely from the eastern Chukchi population. In autumn (September–November), calls were detected in the western Beaufort and northeastern Chukchi, which were likely from both the eastern Beaufort and eastern Chukchi populations. A strong peak at the inshore northeastern Chukchi site occurred in late-November; this peak is likely to be from the eastern Chukchi population. During spring, beluga calls were detected in the northeastern Chukchi and western Beaufort in two distinct vocal peaks (early- and late-May). The timing was consistent with the hypothesis that both vocal peaks were caused by the eastern Beaufort population. This suggests that migration of populations can be discriminated when temporal differences between vocal peaks are large enough to be identified as independent events. Our study results complement and support the population identity of peaks suggested by satellite telemetry, aerial surveys, and other acoustical studies. Passive acoustic monitoring improves our understanding of the migratory timing of beluga populations for management and conservation in a region undergoing rapid change.

Review of the Effects of Offshore Seismic Surveys in Cetaceans: Are Mass Strandings a Possibility?

Displacement of cetaceans is commonly reported during offshore seismic surveys. Speculation concerning possible links between seismic survey noise and cetacean strandings is available for a dozen events but without convincing causal evidence. This lack of evidence should not be considered conclusive but rather as reflecting the absence of a comprehensive analysis of the circumstances. Current mitigation guidelines are inadequate for long-range effects such as displacements and the potential for strandings. This review presents the available information for ten documented strandings that were possibly linked to seismic surveys and recommends initial measures and actions to further evaluate this potential link.