Marine Mammal Science最新文献

The global distribution of Orcinus orca (orcas/killer whales) encompasses populations which differ from each other. Saddle patch shapes and sizes were compared for nearly 4,000 individuals, in 48 geographically or ecologically divided groups/populations/ecotypes (GP/E), in four Ocean Basins. Some Antarctic GP/E had five shapes, contrary to previous studies, which found only one shape in these Southern GP/E. Pacific Resident ecotypes had the highest variation in saddle patch shapes. Globally, the most common shape was the ‘Smooth’ category. Saddle patch sizes were measured using a ratio of the width of the saddle patch compared to the width of the dorsal fin base and averaged within each GP/E. The narrowest saddle patches were observed in New Zealand waters. The widest saddle patches were observed at the Crozet Islands and the Falkland Islands (Islas Malvinas). Globally, we found that the shape and size of saddle patches helped to define various GP/E, reinforcing earlier predictions that this pigmentation may be indicative of population divisions. Our findings may help with describing poorly defined or undescribed ecotypes. Such results may therefore aid assessments by management authorities/policy makers and provide levels of guidance in the creation of conservation or recovery plans.

Pinnipeds have vibrissae with which they can explore their environment. Two vibrissal parameters that differ in pinnipeds are shape and number. Regarding shape, most phocids have undulated vibrissae, whereas the vibrissae of a few phocids, all otariids and walruses are smooth. As there is disagreement with respect to which phocid vibrissae lack the undulation, we systematically collected information on vibrissal type. We have documented that all eared seals we examined, walruses, Mediterranean monk seals, bearded, and leopard seals have smooth vibrissae. All other phocids have undulated vibrissae, except for Ross seals and Hawaiian monk seals, which have partially undulated vibrissae. Moreover, we quantified and documented the existence of vibrissae from photos revealing otariids to have 20–43 mystacial vibrissae/pad, no rhinal vibrissae, 1–2 supraorbital vibrissae above each eye, and phocids to have 15–97 mystacial vibrissae/pad, 0–2 rhinal vibrissae/nostril, 1–9 supraorbital vibrissae above each eye, all averages determined from counts made from photos. Walruses have the maximum number of mystacial vibrissae amounting to 198 vibrissae/pad on average, but almost all walruses lack rhinal and supraorbital vibrissae. Vibrissae were found at the upper lip and on the lower jaw in some pinnipeds.

Beaked whales have recently been reported in the South China Sea but with taxonomic uncertainty due to their ambiguous morphological features. Here, we sequenced three genetic markers, the control region (CR) and cytochrome b (cytb) of the mitochondrial genome and the first intron of the nuclear muscle actin gene ACTA2, of two biopsy samples collected in 2021, and revealed unambiguous clustering with sequences previously attributed to Deraniyagala's beaked whale (Mesoplodon hotaula). Phylogenetic analysis of complete mitogenomes strongly supported the close relationship between the Deraniyagala's beaked whale and the ginkgo-toothed beaked whale (M. ginkgodens). Whole-genome sequencing suggested a high degree of heterozygosity in the Deraniyagala's beaked whale. Ancient inbreeding may have had a greater impact than the recent inbreeding on Deraniyagala's beaked whales, but more samples are needed to draw a firm conclusion. The approximate effective population size of Deraniyagala's beaked whale was found lowest among seven examined ziphiids, which has been experiencing a steady decline since ~300,000 ya. Therefore, we suggest that the conservation status of Deraniyagala's beaked whales should be assessed when essential information is available. The results of our study provide genetic evidence of the live sighting of Deraniyagala's beaked whale in the South China Sea and are fundamental to understanding the morphological, behavioral, and ecological perspectives of this cetacean species.

Deraniyagala's beaked whale, Mesoplodon hotaula, was previously known from eight published strandings and no confirmed live sightings, making it one of the least-known cetaceans. We conducted six cetacean survey cruises in the South China Sea between 2019 and 2023, and during 120 sea-days we recorded 12 sightings of unidentified Mesoplodon. From biopsy samples and acoustic recordings, five sightings were subsequently confirmed as M. hotaula. Using photographs, we provide the first field descriptions and observations of this species. The calf/juvenile has a distinctive facial coloration and dorsal striping pattern that appear to be diagnostic among Indo-Pacific Mesoplodon; among adult males, the dark rostrum of M. hotaula and the distinctively white-tipped beak of ginkgo-toothed beaked whale, M. ginkgodens, distinguish these similar-looking, partially sympatric species. Mean group size was small (3.0, n = 5), with a preference for deep (2,156 m, n = 5), warm (30.3°C, n = 3) water. We update the known distribution of this species, present evidence of fishery interactions, and document the first reported mixed-species Mesoplodon group: a juvenile Blainville's beaked whale M. densirostris associated with four M. hotaula. These sightings identify the South China Sea as a potentially important area for this almost completely unknown species.