True's Beaked Whales, Mesoplodon mirus
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Description & Behavior
True's beaked whales, Mesoplodon mirus (True, 1913), aka wonderful beaked whales, measure 4.9-5.3 m and weigh 1,200-1,400 kg. They are gray in color with lighter gray coloring on their ventral (under) sides. Adults have a dark ring around their eyes and some white areas on their bodies. True's beaked whales in the Southern Hemisphere also have a white area on their dorsal (upper) side behind their dorsal fins, a darker belly, and the tip of their beaks are white. Adult males have a small tooth exposed on either side of their lower jaws. The dorsal fins of True's beaked whales is small and curved with a concave edge. The flukes (tails) of True's beaked whales in the Southern Hemisphere are darker than the rest of their body and also have concave edges. They have no notch in the middle of their tails as with other whale species. Their flippers can be tucked away in a pocket or depression located on the ventral (under) side of their body similar to other beaked whales of the genus Mesoplodon.
Beaked Whales (Family Ziphiidae)
These medium-sized to moderately large whales have a single pair of grooves on their throats. They have distinct snouts, and often the few teeth present are visible only in adult males. They have a single nostril or blowhole. Beaked whales are generally slender with small dorsal fins toward the rear on their backs. The rear edge of their flukes (tails) usually lacks a well-defined notch. These whales are deep divers and are rarely seen. Many species are known only from a few specimens, and little is known about the life history and biology of the group. All members of this family, except Blainville's beaked whales, are difficult to distinguish from each other, and study by museum experts is usually necessary for identification.
World Range & Habitat
True's beaked whales, Mesoplodon mirus, of the Northern Hemisphere are found in temperate waters of the North Atlantic off the coasts of Nova Scotia and Ireland. The Southern Hemisphere populations can be found off the coast of North Carolina, Florida, San Salvador, the Bahamas, and the Canary Islands as well as South Africa, Western Australia, and Victoria. The species does not seem to occur within 30° north or south of the equator, therefore the northern and the southern populations may be entirely separate, a theory supported by their morphological differences.
Mesoplodon mirus have rarely been observed at sea, so very little data exists on the behavior of these animals. Most of the data gathered on this species has been collected from strandings, which are also rare. In May 1993, a pod of three True's beaked whales were observed at sea near Hatteras Inlet, North Carolina in about 600 fathoms of water along a very steep portion of the continental shelf. The lack of sightings of True's beaked whales indicates that they are likely offshore deep divers.
Feeding Behavior (Ecology)
True's beaked whales are thought to prey on cephalopods based on the stomach content examinations of stranded whales.
Conservation Status & Comments
The rarity of True's beaked whales makes them unavailable for commercial exploitation. However, they have been reported as bycatch by the pelagic drift gillnet fishery off the US east coast. Between 1989-1998, 46 beaked whale bycatch moralities were recorded, 4 of which were identified as True's beaked whales.
References & Further Research
Texas Marine Mammal Stranding Network - Corpus Christi Region
CMS: Mesoplodon mirus, True's beaked whale
Center for Cetacean Research and Conservation (CCRC) - Beaked whales (+ videos)
Whale and Dolphin Conservation Society (WDCS)
Research Mesoplodon mirus » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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