Adult male Cuvier's beaked whales (Ziphius cavirostris) engage in prolonged bouts of synchronous diving

Studies of the social behavior of Cuvier's beaked whales (Ziphius cavirostris) are challenging because of their deep-water habitat usually far from shore and the limited time they spend at the surface. The sociality of these deepest diving mammals is of interest, however, especially for our understanding of how social systems evolve in extreme habitats. High levels of scarring suggest that males compete agonistically for access to females and so we predicted that associations among adult males would be unstable due to competitive exclusion. We tested this prediction by evaluating the diving behavior of animals within social groups off Cape Hatteras, North Carolina, considering diving synchrony a proxy for group membership. Using data from satellite-linked depth-recording tags, we found that adult male–male pairs showed extended periods of synchrony in diving behavior, while all pairs that included an adult male with an individual of another age and/or sex dove synchronously for less than a day. We assessed three hypotheses to explain these surprising results: sexual segregation; extended bouts of male–male competition; and the presence of male alliances. Finally, we considered testable predictions to distinguish among these explanations.     

利用mtDNA序列及形态特征重新鉴定福建长乐搁浅喙鲸

<正>中国大陆沿岸属大陆棚水域,常见的齿鲸物种以近岸型的海豚科(Delphinidae)、小抹香鲸科(Kogiidae)及鼠海豚科(Phocaenidae)动物为主(王丕烈,2012),而喙鲸科(Ziphiidae)发现纪录相对较少,近年来仅由王丕烈等(2011)针对喙鲸科的中喙鲸属(Mesoplodon)标本进行检视校正,认为中国大陆沿岸存在柏氏中喙鲸     

Does a lack of observed beaked whale strandings in military exercise areas mean no impacts have occurred? A comparison of stranding and detection probabilities in the Canary and main Hawaiian Islands

Anthropogenic activities must be monitored to determine effects on marine mammal species, but the difficulty lies in how to measure impact. Mass strandings of beaked whales have occurred in association with naval exercises, with two species most affected, Cuvier's (Ziphius cavirostris) and Blainville's (Mesoplodon densirostris) beaked whales. Six such events have occurred in the Canary Islands but there have been no reported mass strandings in Hawai‘i. We assess the hypothesis that factors that influence the likelihood of strandings occurring and/or being detected differ between the Canary and main Hawaiian Islands, such that beaked whale stranding/detection probabilities will be lower in Hawai‘i. On an archipelago-wide basis, nearshore bathymetric comparisons indicate that the Canaries have a greater proportion and a total greater amount of appropriate beaked whale habitat closer to shore, with a steeper slope. Hawaiian shorelines are more dominated by steep cliffs, human population density is much lower, and human population per kilometer of shoreline is 53% lower than in the Canaries. All of these factors suggest that there is a higher probability of a carcass washing onshore and being detected in the Canary Islands. It cannot be concluded that the lack of mass strandings in Hawai‘i is evidence of no impact.     

Changes in spatial and temporal distribution and vocal behavior of Blainville's beaked whales (Mesoplodon densirostris) during multiship exercises with mid‐frequency sonar

The number and distribution of vocalizing groups of Blainville's beaked whales (Mesoplodon densirostris) were analyzed before, during, and after multiship mid‐frequency active sonar operations at the US Navy's Atlantic Undersea Test and Evaluation Center (AUTEC) in the Bahamas. Groups of foraging animals were isolated by detecting their echolocation clicks using an array of bottom‐mounted hydrophones. Two data sets were evaluated consisting of 115 and 240 h of acoustic data in May 2007 and 2008, respectively. Vocal activity was observed to decline during active sonar exercises and increase upon cessation of sonar transmissions in both data sets. Vocal activity did not recover to preexposure levels in the postexposure time period in 2007 nor in the initial postexposure period in the 2008 data set. Clicks detected during sonar operations were generally found to be on the periphery of the hydrophone field and vocal durations declined for those groups that remained on the range in that time period. Receive levels were calculated for several vocal groups of whales and indicated that animals continued to forage when exposed to sonar at levels as high as 157 dB re: μPa.     

Analysis of a Blainville's beaked whale's movement response to playback of killer whale vocalizations

Increasing evidence links exposure to Navy sonar with certain mass stranding events of deep diving beaked whales. Although the cause of these strandings is unknown, one theory suggests that the animals confuse the sonar signals with vocalizations of killer whales, a known predator. Here we analyze the movement patterns of a tagged female Blainville's beaked whale in reaction to playback of killer whale predation calls. During a deep foraging dive, the whale was exposed to a playback of killer whale vocalizations with the source level slowly increased until the whale prematurely ceased foraging. The heading data from the tag were analyzed using a rotation test with a likelihood ratio calculated for a nonparametric kernel density estimate. We found a significant difference (P < 0.005) in the distribution of Δheading (the change in heading averaged over 200 s) after the cessation of the killer whale playback. A test of the angular standard deviation (SD) of the Δheading showed that after the playback, the SD was significantly reduced (P = 0.0064), which indicates that the animal maintained a straighter than normal course for an extended period of time. The prolonged directed avoidance response observed here suggests a behavioral reaction that could pose a risk factor for stranding.     

Behavioral responses of satellite tracked Blainville's beaked whales (Mesoplodon densirostris) to mid-frequency active sonar

The vulnerability of beaked whales (Family: Ziphiidae) to intense sound exposure has led to interest in their behavioral responses to mid-frequency active sonar (MFAS, 3–8 kHz). Here we present satellite-transmitting tag movement and dive behavior records from Blainville's beaked whales (Mesoplodon densirostris) tagged in advance of naval sonar exercises at the Atlantic Undersea Test and Evaluation Center (AUTEC) in the Bahamas. This represents one of the largest samples of beaked whales individually tracked during sonar operations (n = 7). The majority of individuals (five of seven) were displaced 28–68 km after the onset of sonar exposure and returned to the AUTEC range 2–4 days after exercises ended. Modeled sound pressure received levels were available during the tracking of four individuals and three of those individuals showed declines from initial maxima of 145–172 dB re 1 μPa to maxima of 70–150 dB re 1 μPa following displacements. Dive behavior data from tags showed a continuation of deep diving activity consistent with foraging during MFAS exposure periods, but also suggested reductions in time spent on deep dives during initial exposure periods. These data provide new insights into behavioral responses to MFAS and have important implications for modeling the population consequences of disturbance.     

Abundance,survival, and annual rate of change of Cuvier's beaked whales (Ziphius cavirostris) on a Navy sonar range

Bayesian mark-recapture estimates of survival, abundance, and trend are reported for Cuvier's beaked whales (Ziphius cavirostris) using a Navy training range off southern California. The deep-diving beaked whale family is exceptionally vulnerable to mid-frequency active sonar (MFAS), which has been implicated in mass strandings and altered foraging behavior. Extremely low sighting probabilities impede studies of population-level impacts of MFAS on beaked whales. The San Nicolas Basin hosts a Navy training range subject to frequent MFAS use and attracts high densities of Z. cavirostris. An 11-year (2007–2018) photo-identification program leveraged automated acoustic detection and location capabilities on the range's 1,800-km² hydrophone array to enhance capture probability. Estimated population parameters for Z. cavirostris using the range included mean (90% credibility intervals) apparent annual survival of 0.950 (0.899–0.986), annual number of individuals as 121 (71–219), and annual rate of change of −0.8% (−5.6%–4.1%). Simulations show the probability of detecting abundance changes is currently low, but can be greatly improved through continued monitoring and increased effort. Complementary data collection on habitat use and demographic rates in San Nicolas and surrounding basins is also essential to relating direct effects of MFAS use to changes in vital rates and broader population outcomes.     

Echolocation behaviour adapted to prey in foraging Blainville's beaked whale (Mesoplodon densirostris)

Toothed whales echolocating in the wild generate clicks with low repetition rates to locate prey but then produce rapid sequences of clicks, called buzzes, when attempting to capture prey. However, little is known about the factors that determine clicking rates or how prey type and behaviour influence echolocation-based foraging. Here we study Blainville's beaked whales foraging in deep water using a multi-sensor DTAG that records both outgoing echolocation clicks and echoes returning from mesopelagic prey. We demonstrate that the clicking rate at the beginning of buzzes is related to the distance between whale and prey, supporting the presumption that whales focus on a specific prey target during the buzz. One whale showed a bimodal relationship between target range and clicking rate producing abnormally slow buzz clicks while attempting to capture large echoic targets, probably schooling prey, with echo duration indicating a school diameter of up to 4.3m. These targets were only found when the whale performed tight circling manoeuvres spending up to five times longer in water volumes with large targets than with small targets. The result indicates that toothed whales in the wild can adjust their echolocation behaviour and movement for capture of different prey on the basis of structural echo information.     

Resurrection of Mesoplodon hotaula Deraniyagala 1963: A new species of beaked whale in the tropical Indo‐Pacific

We present genetic and morphological evidence supporting the recognition of a previously synonymized species of Mesoplodon beaked whale in the tropical Indo‐Pacific, Mesoplodon hotaula. Although the new species is closely‐related to the rare ginkgo‐toothed beaked whale M. ginkgodens, we show that these two lineages can be differentiated by maternally (mitochondrial DNA), biparentally (autosomal), and paternally (Y chromosome) inherited DNA sequences, as well as by morphological features. The reciprocal monophyly of the mtDNA genealogies and the largely parapatric distribution of these lineages is consistent with reproductive isolation. The new lineage is currently known from at least seven specimens: Sri Lanka (1), Gilbert Islands, Republic of Kiribati (1+), Palmyra Atoll, Northern Line Islands, U.S.A. (3), Maldives (1), and Seychelles (1). The type specimen (Sri Lanka) was described as a new species, M. hotaula, in 1963, but later synonymized with M. ginkgodens. This discovery brings the total number of Mesoplodon species to 15, making it, by far, the most speciose yet least known genus of cetaceans.     

Genetic structure of the beaked whale genus Berardius in the North Pacific,with genetic evidence for a new species

There are two recognized species in the genus Berardius, Baird's and Arnoux's beaked whales. In Japan, whalers have traditionally recognized two forms of Baird's beaked whales, the common “slate‐gray” form and a smaller, rare “black” form. Previous comparison of mtDNA control region sequences from three black specimens to gray specimens around Japan indicated that the two forms comprise different stocks and potentially different species. We have expanded sampling to include control region haplotypes of 178 Baird's beaked whales from across their range in the North Pacific. We identified five additional specimens of the black form from the Aleutian Islands and Bering Sea, for a total of eight “black” specimens. The divergence between mtDNA haplotypes of the black and gray forms of Baird's beaked whale was greater than their divergence from the congeneric Arnoux's beaked whale found in the Southern Ocean, and similar to that observed among other congeneric beaked whale species. Taken together, genetic evidence from specimens in Japan and across the North Pacific, combined with evidence of smaller adult body size, indicate presence of an unnamed species of Berardius in the North Pacific.     

Geographic differences in Blainville's beaked whale (Mesoplodon densirostris) echolocation clicks

Aim

Understanding cetacean species' distributions and population structure over space and time is necessary for effective conservation and management. Geographic differences in acoustic signals may provide a line of evidence for population-level discrimination in some cetacean species. We use acoustic recordings collected over broad spatial and temporal scales to investigate whether global variability in echolocation click peak frequency could elucidate population structure in Blainville's beaked whale (Mesoplodon densirostris), a cryptic species well-studied acoustically.

Location

North Pacific, Western North Atlantic and Gulf of Mexico.

Time period

2004–2021.

Major taxa studied

Blainville's beaked whale.

Methods

Passive acoustic data were collected at 76 sites and 150 cumulative years of data were analysed to extract beaked whale echolocation clicks. Using an automated detector and subsequent weighted network clustering on spectral content and interclick interval of clicks, we determined the properties of a primary cluster of clicks with similar characteristics per site. These were compared within regions and across ocean basins and evaluated for suitability as population-level indicators.

Results

Spectral averages obtained from primary clusters of echolocation clicks identified at each site were similar in overall shape but varied in peak frequency by up to 8 kHz. We identified a latitudinal cline, with higher peak frequencies occurring in lower latitudes.

Main conclusions

It may be possible to acoustically delineate populations of Blainville's beaked whales. The documented negative correlation between signal peak frequency and latitude could relate to body size. Body size has been shown to influence signal frequency, with lower frequencies produced by larger animals, which are subsequently more common in higher latitudes for some species, although data are lacking to adequately investigate this for beaked whales. Prey size and depth may shape frequency content of echolocation signals, and larger prey items may occur in higher latitudes, resulting in lower signal frequencies of their predators.     

CHARACTERIZATION OF BEAKED WHALE (ZIPHIIDAE) AND SPERM WHALE (PHYSETER MACROCEPHALUS) SUMMER HABITAT IN SHELF-EDGE AND DEEPER WATERS OFF THE NORTHEAST U. S.

Sperm whales ( Physeter macrocephalus ) and beaked whales ( Mesoplodon spp. and Ziphius cavirostris ) are deep-diving cetaceans that frequent shelf-edge and Gulf Stream waters off the northeast U. S. coast. Sighting data collected during seven summer (1990, 1991, 1993, and 1995–1998) shipboard surveys were analyzed using a geographic information system to determine habitat use based on bathymetric and oceanographic features. Although sighting rates were lower for beaked whales, both taxa occupied similar habitats. Beaked whales were concentrated at the colder shelf edge, whereas sperm whales were associated with warmer off-shelf water. Mean sighting rates for both taxa were higher in canyon features, but only beaked whale sighting rates were significantly different between canyon and non-canyon habitat (Wilcoxon signed rank test P = 0.007). Within the shared habitat, the two taxa were separated at fine-scale based on oceanographic features.     

Where to stay by night and day: Size-specific and seasonal differences in horizontal and vertical distribution of Chaoborus flavicans larvae

1. Data on the distributions of pelagic and benthic Chaoborus flavicans larvae were gathered in 1994 and tested for their agreement with the predator avoidance hypotheses. The development of all Chaoborus life stages, as well as the horizontal and vertical distribution in the four larval instars, was followed from May until October. We expected the largest larvae to dwell deeper by day, thus avoiding predation by visually foraging fish.
2. In agreement with this prediction body size increased with daytime depth, and this was true both between and within instars. The migration amplitude consequently increased with larval instar.
3. There was also evidence for horizontal migration, mainly in the third but also in the fourth instar.
4. Along a horizontal transect with increasing depth, locations with many benthic larvae had fewer pelagic larvae. Oxygen concentration was a good predictor of maximum benthic larval depth for most of the season but failed to predict their distribution in autumn.     

The extracranial arterial system in the heads of beaked whales,with implications on diving physiology and pathogenesis

Beaked whales are medium‐sized toothed whales that inhabit depths beyond the continental shelf; thus beaked whale strandings are relatively infrequent compared to those of other cetaceans. Beaked whales have been catapulted into the spotlight by their tendency to strand in association with naval sonar deployment. Studies have shown the presence of gas and fat emboli within the tissues and analysis of gas emboli is suggestive of nitrogen as the primary component. These findings are consistent with human decompression sickness (DCS) previously not thought possible in cetaceans. Because, tissue loading with nitrogen gas is paramount for the manifestation of DCS and nitrogen loading depends largely on the vascular perfusion of the tissues, we examined the anatomy of the extracranial arterial system using stranded carcasses of 16 beaked whales from five different species. Anatomic regions containing lipid and/or air spaces were prioritized as potential locations of nitrogen gas absorption due to the known solubility of nitrogen in adipose tissue and the nitrogen content of air, respectively. Attention was focused on the acoustic fat bodies and accessory sinus system on the ventral head. We found much of the arterial system of the head to contain arteries homologous to those found in domestic mammals. Robust arterial associations with lipid depots and air spaces occurred within the acoustic fat bodies of the lower jaw and pterygoid air sacs of the ventral head, respectively. Both regions contained extensive trabecular geometry with small arteries investing the trabeculae. Our findings suggest the presence of considerable surface area between the arterial system, and the intramandibular fat bodies and pterygoid air sacs. Our observations may provide support for the hypothesis that these structures play an important role in the exchange of nitrogen gas during diving. J. Morphol. 277:5–33, 2016. © 2015 Wiley Periodicals, Inc.     

Occurrence and social structure of Baird's beaked whales,Berardius bairdii,in the Commander Islands,Russia

The social structure of Baird's beaked whales is completely unstudied, and it is unknown if either females or males form long‐term social associations or occur in stable groups. In this paper we summarize our observations of individually identified animals over the span of 6 yr to provide insight on their long‐term social structure. We have identified 122 whales, with 28 of them encountered three times or more and thus included in the analysis of social structure. We found that the whales exhibited nonrandom patterns of social associations with some individuals preferentially associating with each other. Whales with more scarred skin had higher maximum association coefficients, which indicates that older animals and/or males were more inclined to form stable associations. Cluster analysis with a modularity test for gregariousness divided the whales into four clusters. Whales from the same clusters did not always occur together, but some individuals retained stable associations over several years. The strength of social relationships decayed over periods of months, with between‐year relationships showing little deviation from what would be expected if association was random. Generally these findings do not correspond to a stable society with fixed groups but instead suggest a fission‐fusion society with some stable alliances.     

The change in phototactic behaviour of a Daphnia magna clone in the presence of fish kairomones: the effect of exposure time

Using a clone that responds to the presence of fishkairomones by a pronounced change in phototacticbehaviour, we determined how fast a change to morenegatively phototactic behaviour occurs in Daphnia magnaadults that are exposed to a highconcentration of fish kairomones. Kairomone exposedanimals showed an approximately linear decrease in thevalue of the phototactic index with time. Though theresponse was almost immediate, it took two hoursbefore the difference between fish-induced and controlanimals was significant. Extrapolation of the observedresponse indicates that a maximal change inphototactic behaviour, equivalent to animals that havebeen cultured in the presence of fish kairomones sincebirth, occurs after about 13 hours exposure. Weconclude that the predator-induced change in dielvertical migration of zooplankton is fast, and isfully developed in less than a day. The response timeto fish kairomones of Daphnia is shorter forphototactic behaviour than for life history traits,which may have important consequences with respect tothe evolution of trait-dependence in induced defenceresponses.     

Behavior of Cape fur seals (Arctocephalus pusillus pusillus) in relation to temporal variation in predation risk by white sharks (Carcharodon carcharias) around a seal rookery in False Bay,South Africa

The marked differences in predation risk posed by white sharks (Carcarodon carcarias) at island rookeries of Cape fur seals (Arctocephalus pusillus pusillus) offer a quasi‐experimental design within a natural system for exploring how prey adjust their behavior in response to temporal variation in predation risk. Here we compare movement of juvenile and adult Cape fur seals at a high risk (Seal Island) and low risk (Egg Island) rookery. We further compare juveniles and adults at Seal Island in low and high risk seasons and at low and high risk times of day within those seasons. Adult fur seals at Seal Island avoided traversing the zone of high white shark predation risk during the high risk period (0700–0959) in the season of high risk (winter), but not during the low risk season (summer). By contrast, adult fur seals at Egg Island showed no temporal discretion in either season. Unlike juvenile fur seals at Egg Island, juveniles at Seal Island adjusted their temporal movement patterns to more closely mimic adult seal movement patterns. This suggests that exposure to predators is the primary driver of temporal adjustments to movement by prey species commuting from a central place.     

Variability and possible adaptive significance of day-time vertical distribution ofLeptodora kindtii (Focke) (Cladocera) in a shallow eutrophic lake

The day-time vertical distribution of different size classes ofLeptodora kindtii in Tjeukemeer was studied during two contrasting years: 1978 and 1979. During the first year (1978) the predation pressure exerted by the planktivorous fish was rather high, whilst this was ca. 15 times lower during 1979. The diel vertical migration of different size classes ofLeptodora, was studied twice during 1979. Both studies support the predator avoidance hypothesis and also emphasize the idea that diel vertical migration is a dynamic rather than a fixed behaviour trait within a population.