Diane Claridge

Beaked Whales Respond to Simulated and Actual Navy Sonar

Beaked whales have mass stranded during some naval sonar exercises, but the cause is unknown. They are difficult to sight but can reliably be detected by listening for echolocation clicks produced during deep foraging dives. Listening for these clicks, we documented Blainvilles beaked whales, Mesoplodon densirostris, in a naval underwater range where sonars are in regular use near Andros Island, Bahamas. An array of bottom-mounted hydrophones can detect beaked whales when they click anywhere within the range. We used two complementary methods to investigate behavioral responses of beaked whales to sonar: an opportunistic approach that monitored whale responses to multi-day naval exercises involving tactical mid-frequency sonars, and an experimental approach using playbacks of simulated sonar and control sounds to whales tagged with a device that records sound, movement, and orientation. Here we show that in both exposure conditions beaked whales stopped echolocating during deep foraging dives and moved away. During actual sonar exercises, beaked whales were primarily detected near the periphery of the range, on average 16 km away from the sonar transmissions. Once the exercise stopped, beaked whales gradually filled in the center of the range over 2–3 days. A satellite tagged whale moved outside the range during an exercise, returning over 2–3 days post-exercise. The experimental approach used tags to measure acoustic exposure and behavioral reactions of beaked whales to one controlled exposure each of simulated military sonar, killer whale calls, and band-limited noise. The beaked whales reacted to these three sound playbacks at sound pressure levels below 142 dB re 1 µPa by stopping echolocation followed by unusually long and slow ascents from their foraging dives. The combined results indicate similar disruption of foraging behavior and avoidance by beaked whales in the two different contexts, at exposures well below those used by regulators to define disturbance.

Kinship as a basis for alliance formation between male bottlenose dolphins, Tursiops truncatus, in the Bahamas

Alliances between reproductive males have been described in both cetacean and terrestrial mammal societies, and kin selection theory has often been invoked to explain these stable male coalitions. However, recent studies of bottlenose dolphins, Tursiops aduncus, in Australia suggest that mechanisms other than kinship are fundamental in the formation of male alliances. We supplemented skin biopsy sampling with the collection of faecal samples from individually recognized wild bottlenose dolphins, T. truncatus, to assess the role of kin selection in alliance membership in the northeast Bahamas. Stable alliances between pairs of males were identified based on association analyses of individual photoidentification data collected over 4 years. Molecular genetic analyses of tissue samples revealed highly significant correlations between patterns of association and both mitochondrial DNA haplotype identity and microsatellite relatedness, indicating that males within long-term alliances are more closely related than expected by chance. These data reinforce the high degree of plasticity previously reported within the genus Tursiops, and suggest that social and ecological differences between populations can markedly affect the role of kin selection in determining social alliances between male bottlenose dolphins.  2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.

Amplifying dolphin mitochondrial DNA from faecal plumes

© 1999 Blackwell Science Ltd, Molecular Ecology, 8, 1753–1768 for paternity analyses. Six loci that did not amplify reliably but may be useful with different primers are (repeat array followed by GenBank Accession no.): (GA)13 (AF143977); (TG)13 (AF143978); (CT)19 (AF143981); (TG)11 (AF143983); (GA)24 (AF143984); and (CT)23(AT)12 (AF143985). The five loci used for paternity yielded 77 alleles with a mean of 15 alleles per locus. Observed and expected heterozygosities ranged from 0.49 to 0.94. Hardy–Weinberg equilibrium was tested with Fisher’s exact test of genepop version 3.1d (Raymond & Rousset 1995). A significant excess of homozygotes was observed in three populations for DE48 and in five populations for DE54 (Table 1), presumably the result of null alleles. The expected exclusion probabilities for single loci ranged from 0.23 to 0.87 with a multilocus expectation of > 0.995 (Marshall et al. 1998). Together, these loci provided enough variation to resolve paternity for a large portion of the D. excelsa seed population.

Male-male aggression renders bottlenose dolphin ( Tursiops truncatus ) unconscious

Intraspecie c aggression constitutes a signie cant proportion of conspecie c behaviours among many mammal species. Agonistic interactions among male bottlenose dolphins ( Tursiops truncatus ) have been documented in several di Verent regions, including escalated aggression involving coalitions comprised of several males. However, despite many hours of direct observation most of these encounters are evidenced by minor injuries and often, physical wounds are not visible. Herein, we describe a unique encounter involving a long-term male alliance competing with a ‘ solo’ male that resulted in the temporary loss of consciousness of the lone male following repeated physical blows to his head region. This observation supports the increased e tness experienced by males in alliances and illustrates the potential severity of aggressive interactions among adult bottlenose dolphins.

Killer whale ( Orcinus orca ) occurrence and predation in the Bahamas

Killer whales (Orcinus orca) have a cosmopolitan distribution, yet little is known about populations that inhabit tropical waters. We compiled 34 sightings of killer whales in the Bahamas, recorded from 1913 to 2011. Group sizes were generally small (mean 1⁄4 4.2, range 1⁄4 1–12, SD 1⁄4 2.6). Thirteen sightings were documented with photographs and/or video of sufficient quality to allow individual photo-identification analysis. Of the 45 whales photographed, 14 unique individual killer whales were identified, eight of which were re-sighted between two and nine times. An adult female (Oo6) and a now-adult male (Oo4), were first seen together in 1995, and have been re-sighted together eight times over a 16-yr period. To date, killer whales in the Bahamas have only been observed preying on marine mammals, including Atlantic spotted dolphin (Stenella frontalis), Fraser’s dolphin (Lagenodelphis hosei), pygmy sperm whale (Kogia breviceps) and dwarf sperm whale (Kogia sima), all of which are previously unrecorded prey species for Orcinus orca.

Detection of beaked whales using near surface towed hydrophones: prospects for survey and mitigation

Beaked whales are extremely difficult to sight at sea and this hampers attempts to study them, and makes real time mitigation difficult. Passive acoustic monitoring could improve detection efficiency. Blainvilles beaked whales, (Mesoplodon densirostris) are known to produce most of their vocalizations at depth. They are routinely detected on bottom mounted hydrophones arrays but the extent to which they can be detected using near‐surface hydrophones is not known. Continuous recordings were made at a sampling rate of 192 kHz from towed hydrophone arrays during line transect surveys in the Bahamas in conjunction with teams monitoring bottom‐mounted hydrophones at the AUTEC Tongue of the Ocean navy range. A beaked whale click detector and classifier was developed within Rainbow Click and PAMGUARD and this was both run in real time and used to analyze recordings to pick out beaked whale click trains. Detected click trains correlated well with detection of beaked whales on bottom‐mounted hydrophones. Three sp...

Effects of sound on the behavior of toothed whales

We report initial results from a study on behavioral responses of beaked and other whales to sonar and other sounds. This research is designed to provide new science‐based approaches for mitigating the risk of sonar to beaked and other whales. The study was conducted at the Atlantic Undersea Test and Evaluation Center (AUTEC) range near Andros Island in the Bahamas, where Blainvilles beaked whales (Mesoplodon densirostris) can regularly be detected using passive acoustic monitoring of their echolocation clicks. Tags recorded sound at the whale and behavior of the whale. Data were collected from 10 tag deployments, 6 on Blainvilles beaked whales and 4 on pilot whales. 109 hours of data were collected from tags, 74 hours from beaked whales and 34 hours from pilot whales. Playbacks of mid‐frequency sonar and killer whale calls were performed on 3 of the tagged whales, 1 beaked whale and 2 pilot whales. The tagged beaked whale responded to both sonar and killer whale sounds by premature cessation of clicking during foraging dives (RL = ∼117 dB re 1 μPa for the killer whale sound, ∼145 dB for the sonar), and an unusually slow and long ascent.

Data from ‘Estimating group size from acoustical footprint to improve Blainville’s beaked whale abundance estimation’

• gID a group ID • cs the group size • conf the confidence in the group size (1-best; 2-medium;3-low) • maxcount the maximum number of clicks in a single hydrophone over the hydrophones the group was detected • meancount the mean number of clicks detected per hydrophone • nhyd the number of hydrophones the group as detected on • cdur the duration of the vocal period • nclicks the total number of clicks detected • crate the total detected click rate nclicks/cdur • wisk whether a Wiskey hydrophone was involved in the detection • direction whether a bidirectional phone was involved in the detection

Physiological, morphological, and ecological tradeoffs influence vertical habitat use of deep-diving toothed-whales in the Bahamas

Dive capacity among toothed whales (suborder: Odontoceti) has been shown to generally increase with body mass in a relationship closely linked to the allometric scaling of metabolic rates. However, two odontocete species tagged in this study, the Blainville’s beaked whale Mesoplodon densirostris and the Cuvier’s beaked whale Ziphius cavirostris, confounded expectations of a simple allometric relationship, with exceptionally long (mean: 46.1 min & 65.4 min) and deep dives (mean: 1129 m & 1179 m), and comparatively small body masses (med.: 842.9 kg & 1556.7 kg). These two species also exhibited exceptionally long recovery periods between successive deep dives, or inter-deep-dive intervals (M. densirostris: med. 62 min; Z. cavirostris: med. 68 min). We examined competing hypotheses to explain observed patterns of vertical habitat use based on body mass, oxygen binding protein concentrations, and inter-deep-dive intervals in an assemblage of five sympatric toothed whales species in the Bahamas. Hypotheses were evaluated using dive data from satellite tags attached to the two beaked whales (M. densirostris, n = 12; Z. cavirostris, n = 7), as well as melon-headed whales Peponocephala electra (n = 13), short-finned pilot whales Globicephala macrorhynchus (n = 15), and sperm whales Physeter macrocephalus (n = 27). Body mass and myoglobin concentration together explained only 36% of the variance in maximum dive durations. The inclusion of inter-deep-dive intervals, substantially improved model fits (R2 = 0.92). This finding supported a hypothesis that beaked whales extend foraging dives by exceeding aerobic dive limits, with the extension of inter-deep-dive intervals corresponding to metabolism of accumulated lactic acid. This inference points to intriguing tradeoffs between body size, access to prey in different depth strata, and time allocation within dive cycles. These tradeoffs and resulting differences in habitat use have important implications for spatial distribution patterns, and relative vulnerabilities to anthropogenic impacts.