[3] Beaked whales are part of the family Ziphiidae, which are the second most diverse group out of all marine mammals with over 20 species currently recognized.
The genus name Mesoplodon comes from the Greek meanings of meso- (middle), - hopla (arms), - odon (teeth), and may be translated as 'armed with a tooth in the center of the jaw'.
Perrin's beaked whales have not definitively been recorded alive by scientists; however, its appearance is known from beached specimens.
[4] The ventral side of the tail flukes are light gray with converging striations and a white patch around the umbilicus (navel).
[4] A photograph of a possible living specimen - one of the two observed in 1976 - is featured in Rice (1978: 95) as "Mesoplodon carlhubbsi", a distinctly larger species also native to the waters off California.
[8] In Perrin's beaked whale, the teeth are located near the tip of the lower jaw and are roughly equilateral triangles when viewed laterally (from the side) in the jaw, which resembles the font teeth of Baird's beaked whale (Berardius bairdii) more than other Mesoplodon species.
[4] Like other mesoplodont whales, male M. perrini have a set of tusk-like teeth that originate from the lower jaw (see image).
A series of long, white scars along the flank of the adult male specimen brought to the conclusion that tusks may play a role in intrasexual competition.
[10] Currently (2019), Perrin's beaked whales have only been found near North Pacific waters off the coast of central and southern California.
Stranded Perrin's beaked whales have been found along the Californian coast between Torrey Pines State Natural Reserve, just north of San Diego (32°55’N, 117°15’W) and Fisherman's Wharf, Monterey (36°37’N, 121°55’W).
Even though current data suggest an eastern North Pacific distribution, there are too few records to date to draw any conclusions on this.
The habitat preferences of other beaked whales suggest M. perrini can primarily be found in oceanic waters that are over 1,000 m in depth.
Again, Perrin's beaked whales have not definitely been recorded alive by scientists, so the limited information known about the species is derived from dead individuals that are beached.
Little is known about the social structure, reproduction, age of sexual maturity, or lifespan of the Perrin's beaked whales, but scars on the bodies of males suggest aggressive competitive behavior.
The largest Perrin's beaked whale calf, LACM 088901, at 2.45 m of length, appeared to be independent from its mother.
[citation needed] Perrin beaked whales are thought to produce a species-specific frequency modulated (FM) echolocation pulse of BW43.
[14] Within a passive acoustics study, signals of BW43 were only detected in southern California at deep sites (1100–1300 m) and are thought to be produced by Perrin's beaked whale, known only from Californian waters.
[5] Declines are hypothesized to have occurred from the effects of incidental mortality from fishing, impacts of anthropogenic noise (Navy sonar), and ecosystem changes.
[5] Since then, the population size of Mesoplodon beaked whales has increased from a mean of 1230 in 2001 to 3439 in 2014 within California Current waters off the U.S. West Coast.
[4] Bycatch is likely one of the main threats to this deep-water species due to it causing harm or death to whales entangled in fishing gear.
With scant data at hand, it still appears the best odds of encountering small beaked whales of this species is during the summer months in the area between Santa Catalina and San Clemente Islands and the mainland.