Mesoplodon

Diversity

Mesoplodon whales belong to the Family Ziphiidae and have fourteen species within their genus. despite being one of the most diverse groups of marine mammals, astonishingly little is known about them. They are often identified by a combination of their head and skull shape and then identity refortification by molecular genetic analysis, to prevent misidentification. They occupy most oceanic environments, excluding the coldest arctic oceans. They use echolocation to help find their food and move around in their environments at ease. Species within Mesoplodon are a smaller species of whales, ranging in size from about four meters to about six meters in length. Trends show that males use their beaks and teeth to fight for dominance and hierarchies amount their groups.

Geographic Range

Species within the Mesoplodon genus are quite widespread. They generally reside deeper than 2,000 meters in almost all of the oceans of the world, excluding the coldest waters found near the Arctic. They can also occasionally be found in the 200-meter to 2,000-meter region of the continental slope, but almost never pass over into the continental shelf region. Individual species distribution is more localized, often residing in a single ocean or hemisphere. Studies have shown that certain species residing at cooler, higher latitudes partake in limited seasonal migration to warmer, lower latitudes during the winter.

• Biogeographic Regions
• indian ocean
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • native native
• mediterranean sea
  • native native

• Other Geographic Terms
• cosmopolitan cosmopolitan

Habitat

Not much is known among the Mesoplodon genus, in regards to habitat, however, there is a general consensus that researchers have been able to determine through the tagging and tracing of these marine mammals. All species within the genus occupy the same type of habitat, they are found in deep water oceans across the world and can occur in and around oceanic islands, the continental slope, and even submarine canyons. This means they are generally in waters with a depth of 200 meters to 2,000 meters, they rarely are at depths shallower than 200 meters, in which they'd pass over the continental shelf. They mostly occupy warm weathered-tropical oceanic regions, but some do stray out towards cooler waters, they do tend to avoid the artics though. In turn, some of the further-reaching species do undergo mild migration to warmer habitats during the winter months.

• Habitat Regions
• temperate temperate
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic

Systematic and Taxonomic History

The connection between Mesoplodon and other taxa is relatively unknown. This taxon does have some synonyms including Dioplodon , Neoziphius , Nodus , all of which were unaccepted by the scientific community.

Physical Description

The species in the Mesoplodon genus has a number of defining characteristics, especially in relation to their skulls. They have a long rostrum creating the beaked appearance that provides their common name. Their rostrums also vary in shape, size, and teeth placement. These specific skull characteristics can vary based on specific species, gender, and can be important in males when it comes to hierarchy. Species in this genus are smaller in size compared to other species and genera of whales. They have a size range between 3.9 meters and 6.2 meters. There is not enough data, since there is little known on this genus, to know if this size variation is based on sex, but in the few available cases, it appears that the females are slightly larger, which is common for the Ziphiid family that Mesoplodons belong to. Mesoplodons have one dorsal fin that has a triangular shape about two-thirds down their spindle-shaped body. They have small narrow flippers. Along their back, they have a semi-circle blowhole that isn't always symmetric. As far as coloring goes, the young and females are the most indistinguishable, they have a gray-ish brown dorsal area and become paler on the ventral side, this nondescript color causes them to blend in as sea and while stranded on the beach. In contrast, adult males are more identifiable if seen in the wild as they have more distinguished colors and patterns, most often consisting of black and/or white patches on different parts of the body based on species. These coloring patterns in males can be caused by two things, normal pigments and their disposition or the coloration can result from scarring. Males often have color patches to define anatomical attributes. The majority of the Mesoplodon species have 3 sexually dimorphic traits. The first is those functioning teeth and is only seen in adult males. The second is that there is extensive secondary ossification in the mesorostral canal of adult males. Lastly, the more extensive body scaring occurs in copious amounts in adult males.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger
• sexes colored or patterned differently

Reproduction

Males are able to potentially increase their evolutionary fitness through partaking in mating with multiple females. this leads to males dispersing themselves based on the distribution of fertile females. Mesoplodons , like many other Cetaceans, subscribe to polyandrous or polygynous mating systems. Mesoplodons do not live monogamous lifestyles, generally females birth a single offspring per calving event. Many species within the Mesoplodon species mate according to breading hierarchies that are created through the intraspecies fighting among males. These fights are often to defend territories that the females value and defend the females themselves, but there's not much evidence to show that males fight to protect their females from predators. The male fighting for female attention allows the determination of the male's genetic quality, how ready they are to breed, their access to resources, and their dominance.

• Mating System
• polyandrous polyandrous
• polygynous polygynous
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Due to the lack of knowledge and research on this genus not much is known regarding Mesoplodon reproduction, including their estrous cycles, fertilization and implantation process, or their gestational period. It has been predicted that they have an average litter size of one and that they are most likely to give birth during the spring or summer, and due to their polyestrous nature females have one birth per calving event. As far as Mesoplodon reproduction systems go, females have ovaries that weigh presumable around 12 grams when mature, and males have small, compressed testes that lay enclosed at the end on a long enclosed pouch.

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual

There is insufficient data regarding the parental investment among the Mesoplodon genus, therefore this is an overview of the parental investment among the Cetacea order they belong to. Females generally distribute themselves in relation to the recourses they need for their offspring to survive, these resources include breeding site availability and food. The males are typically uninvolved due to the anonymity they uphold during fertilization, due to it being internal. There is some evidence to show that in certain groups young can stay with their mothers for life and adopt their maternal behaviors.

• Parental Investment
• female parental care female parental care
• pre-fertilization
  • protecting
    • male
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female
• maternal position in the dominance hierarchy affects status of young

Lifespan/Longevity

Like much else in the genus Mesoplodon not much is known about their lifespan and longevity, they are however predicted to live relatively long lives based on the little data that has been collected. Data was collected on a specimen of Mesoplodon europaeus , and it was found to have a number of tooth layers that lead researchers to believe it was 27 years old at a minimum. In addition to this, a Mesoplodon densirostris female was believed to be around 9 years of age, also based on tooth layers, and had only just come to the age of sexual maturity. Not much-recorded data on parasites or diseases in their genus, although Osteomyelitis, a bone infection that causes swelling, has been recorded twice. Some common endo and ectoparasites include large infestations of nematodes and/or cestodes in their kidneys and cyamids.

Behavior

Researchers have been able to gather quite a bit of behavioral data through observation recently. They have many behaviors that have been observed, the most common being that they often slowly swim away from marine vessels, when they are undisturbed however, they have been reported to roll several times before disappearing again back under the surface. They are often spotted breaching the surface in groups, which scientists believe indicate that they communicate underwater while foraging for food with the use of echolocation. It is believed that the males are using their teeth like elephant tusks to fight in the hierarchical battles, especially when mating, this, however, has not been seen by humans during observation, this is all based on the scarring that is seen in males. Most recently technology has been used to identify how long whales in this genus can remain underwater and how deep they are going. In one study a Mesoplodon densirostris was recorded in Hawaii having a regular dive time of about 50-70 minutes while reaching a maximum depth of around 1400 meters. Meanwhile, in a different study, another Mesoplodon densirostris was recorded spending double that amount of time in shallower waters potentially recovering from the oxygen debt from the longer and deeper dives.

• Key Behaviors
• natatorial natatorial
• motile motile
• migratory migratory
• social social
• dominance hierarchies dominance hierarchies

Communication and Perception

Beaked Whales belonging to the Mesoplodon genus communicate primarily through echolocation. They are using echolocation, which is communication via the production of sound, mainly as a way to forage, locate, and catch prey. It has been estimated that they can identify thousands of organisms through the use of echolocation per foraging dive, and they can do this at a range of about 15 meters. As far as Mesoplodon vocalizations, it has only been recorded in two species Mesoplodon densirostris and Mesoplodon carlhubbsi . The Mesoplodon densirostris is recorded to have two different but distinct click types that can be associated with their foraging phases.

• Communication Channels
• acoustic acoustic

• Other Communication Modes
• vibrations vibrations

• Perception Channels
• tactile tactile
• acoustic acoustic
• echolocation echolocation
• vibrations vibrations
• chemical chemical

Food Habits

From a few encounters where researchers have been able to observe Mesoplodon stomach contents, it appears that they consume small mesopelagic squid primarily. Some species have been found to have eaten fish from the mesopelagic and benthopelagic regions as well, indicating that some species may have diets that are comprised primarily of fish. They are known to catch prey at depths past 200 meters using a series of echolocation clicks. These hypotheses were reaffirmed by a study of North Atlantic Mesoplodon species that showed the diets of those 8 species studied their stomach contents were dominated by 98.5% being comprised of mesopelagic and benthopelagic fishes whereas only a measly 1.5% contained cephalopods.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore

• Foraging Behavior
• stores or caches food stores or caches food

Predation

Mesoplodons find and capture prey mainly through echolocation clicks. Mesoplodons are able to navigate narrow fields of 20 degrees through radiating sounds by sampling 1.5 to 3 clicks per meter traveled. By doing this they can select and approach prey using a minimum of 60 clicks. This has resulted in Mesoplodons being able to classify prey at more than a 15-meter range, having this large of a detection range paired with their swimming speed created a mode of sensory-motor operation allowing them to optimize their energy during long and deep dives. In comparison to air, sound travels at a rate of 4.5 times faster underwater which helps enhance the echolocation abilities of Mesoplodon whales. Echolocation is the primary, sometimes only, sensory method in Mesoplodons , but due to its high success rate, it is suitable to be their method for predation. As far as their predators, it is believed their primary predators are orcas, also known as Killer Whales, while there has not been great observation in this regard or how Mesoplodons avoid their predaotors.

Ecosystem Roles

Mesoplodons do not have a huge impact on their ecosystem, at least no data on their ecological impact could be found. They are not parasitic to other animals and do not use other organisms as hosts. They do host a number of endo- and exo-parasites. They act as prey in the food chain for Orcas and help regulate fish and squid populations by acting as predators for them, past this, their ecosystem roles are not of other major categories.

Economic Importance for Humans: Positive

The Mesoplodon genus does not provide much positive economic value to humans. They aren't something humans are fishing for, although they are occasionally caught via bycatch, nor do they provide any forms of shelter. Due to the nature that Mesoplodon are able to spend most of their time underwater they are not often available for tourists to see. Scientists are interested in further studying these organisms as they are widely understudied.

Economic Importance for Humans: Negative

There are no known adverse effects of Mesopoodon on humans.

Conservation Status

Mesoplodon have not been able to be reliably identified at sea making it incredibly difficult to determine accurate population status, there are some bases for them not being as rare as sighting records would lead scientists to believe based on data gathered from strandings. There are two main threats to the Mesoplodon genus that has been created by humans, those being anthropogenic noise and bycatch. Anthropogenic noise coming from seismic surveys and military mid-frequency sonars can lead to interference with their echolocation. Whereas bycatch occurs when fishermen accidentally catch them in nets while trying to catch other marine organisms.

Additional Links

Encyclopedia of Life

Contributors

Meredith Martin (author), Colorado State University, Audrey Bowman (editor), Colorado State University.

References

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Fishery Bulletin

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