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.     

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.     

A novel gammaherpesvirus associated with genital lesions in a Blainville's beaked whale (Mesoplodon densirostris)

An adult male Blainville's beaked whale (Mesoplodon densirostris) was found stranded on the Atlantic coast of the USA on 28 January 2004. Necropsy revealed a focal papilloma-like penile lesion, the cells from which revealed single 4-6 microm basophilic intranuclear inclusions. Total DNA extracted from lesion material was tested using a pan-herpes-virus PCR assay that targets the DNA polymerase gene and found to be positive. When the amplified DNA fragment was cloned, sequenced, and compared to GenBank-deposited herpesvirus DNA polymerase sequences, the detected virus was determined to be a distinct member of the Gammaherpesvirinae subfamily of herpesviruses. This new virus, tentatively named Ziphiid herpesvirus type 1, was associated with but not determined to be the cause of genital disease in the Blainville's beaked whale.     

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.     

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.     

Partial characterization of the hemoglobin from Hubbs' beaked whale (Mesoplodon carlhubbsi)

• 1.1. Blood samples were obtained from an adult female Hubbs' beaked whale and her fetus.
• 2.2. Two major hemoglobins were demonstrated by cellulose acetate electrophoresis and were purified by ion exchange chromatography from each specimen.
• 3.3. The relative amounts of these components were different in the adult and fetus.
• 4.4. Both of these hemoglobins have a higher affinity for oxygen than normal human hemoglobin.
• 5.5. Maternal and fetal hemoglobins were separated and the N-terminal amino acid of each of these hemoglobins was found to be valine.
• 6.6. Tryptic peptide separation and amino acid analyses of the purified polypeptide chains indicated that the hemoglobins of the fetal sample were identical to those of the maternal.

     

Re-identification of the supposed True's beaked whale Mesoplodon mirus from Scotland

In the first week of January 1931 a beaked whale (Family Ziphiidae) stranded at Gierinish, South Uist, Outer Hebrides, was identified as a True's beaked whale Mesoplodon mirus . This stranding is referred to frequently in the cetacean literature, either directly or indirectly. Re-examination of the skull of this specimen reveals characters unique to Cuvier's whale Ziphius cavirostris and not shown by any Mesoplodon . Therefore, there is no known stranding of True's beaked whale in Britain.     

Blue-Green color and composition of stejneger's beaked whale (Mesoplodon stejnegeri) milk

• 1.1. Two hundred ml of milk were obtained from a lactating Stejneger's beaked whale stranded at Ninilchik, Alaska on 21 Oct, 1980.
• 2.2. Total solids (41%) were similar to values reported for sperm and belukha whales, while fat (17%) was half as great and crude protein (17%) was 2–4 times greater than in milk of these species. Lactose was not detected.
• 3.3. Calcium (0.22%) was greater than reported for pigmy sperm whales but less than for blue whales. Phosphorus (0.07%) was less than for any of the above species. Sodium and potassium concentrations were 0.13% and 0.11%, respectively.
• 4.4. Values (μg/g) for other elements analyzed (magnesium, 42; iron, 35; copper, 2.6; zinc, 1.5; manganese, 0.3; selenium, 0.36) have not been reported for whale milk.
• 5.5. Based on SDS-gel electropherograms, this whale milk did not contain a whey protein corresponding to cattle milk α-lactalbumin.
• 6.6. A blue-green pigment in the milk was identified as biliverdin.

     

Mycoplasma species isolated from harbor porpoises (Phocoena phocoena) and a Sowerby's beaked whale (Mesoplodon bidens) stranded in Scottish waters

Mycoplasma species were recovered from 10 cetacean carcasses that stranded around Scotland. Mycoplasma phocicerebrale was isolated from the lungs of three harbor porpoises (Phocoena phocoena) as well as from the liver of one of these animals. Novel Mycoplasma spp. were isolated from the lungs of five additional harbor porpoises and the kidney of another. In addition an isolate closely related to Mycoplasma species 13CL was obtained from the kidney of a Sowerby's beaked whale (Mesoplodon bidens). The role of these Mycoplasma species in the disease of cetaceans, their host specificity, diversity, and any relation to cetacean strandings are unknown.     

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.     

Color patterns in white‐beaked dolphins (Lagenorhynchus albirostris) from Iceland

Few studies have examined the natural complex pigmentation patterns of white‐beaked dolphins. From 2002 to 2014, whale‐watching trips in Iceland provided a platform of opportunity to collect a large body of photographs of free‐ranging individuals from a single area of distribution for this species. Based on 823 images, 571 individuals showing one or more color components were identified, and assigned to the following four age classes: adults (n = 437), juveniles (n = 109), calves (n = 14), and neonates (n = 11). A total of 26 color components were observed and described: seven terms previously applied to white‐beaked dolphins, 12 previously applied to other dolphin species, and seven newly defined terms. Results showed that each age class could be positively identified by differences in specific color components, some of which were exclusive. Therefore, color patterns may prove useful in estimating maturity in free‐ranging white‐beaked dolphins. This tool could be further refined through assessment of a wide sample of freshly stranded specimens of known sex and age, which could reveal new age class‐specific components, as well as sexually dimorphic characteristics not seen here. Geographic variation should be investigated by comparing image data sets and stranded animals from different parts of the North Atlantic.     

High concentration of long‐snouted beaked whales (genus Messapicetus) from the Miocene of Peru

Abstract: Eight skulls of beaked whales (Cetacea, Odontoceti, Ziphiidae), in six cases associated with elements of the mandible, were collected from a limited area (about 1.5 km²) and roughly from the same stratigraphic horizon at Cerro Colorado, 35 km south‐south‐west of the city of Ica (Peru), where the late Middle Miocene basal strata of the Pisco Formation crop out. They represent the highest concentration reported of fossil Ziphiidae. These finely preserved Cerro Colorado fossils are described and assigned to a new species Messapicetus gregarius, together with another specimen collected from sediments of the same age at Cerro la Bruja (33 km south‐east to Cerro Colorado). Messapicetus gregarius shares with M. longirostris Bianucci, Landini and Varola, 1992 (Tortonian of Italy), an extremely elongated rostrum, but is clearly different from the Italian species in the more distinct maxillary tubercle and prominential notch, the more robust premaxillary crest, and the abrupt ventrolateral descent of the medial margin of the maxilla from the vertex. A parsimony analysis reveals that Messapicetus belongs to a basal clade, which includes other ziphiids with a dorsally closed mesorostral groove and prenarial basin. The high concentration of specimens belonging to the same species (some of them tentatively identified as adult males and females), combined with the presence of a calf, supports the hypothesis of site fidelity; these cetaceans might have lived in a limited region for a long period for both breeding and feeding. Besides the eight specimens of M. gregarius, strata at Cerro Colorado include many other cetacean remains (with several specimens of the pontoporiid Brachydelphis including a foetus), pinnipeds, turtles, fishes, and birds.