Taxonomy and Range

Kingdom: Animalia, Phylum: Chordata, Class: Mammalia, Order: Cetacea, Suborders: Mysticeti; Odontoceti.

There are currently about 90 recognised cetacean species globally of which the majority are Odontoceti. Whales, dolphins and porpoises are terms used historically to describe different families of cetacean, but the taxonomic definition of whales, dolphins and porpoises is not clear. The taxon Mysticeti contains only whales and only those that possess baleen instead of teeth. Mysticetes or baleen whales all tend to be relatively large, feeding on plankton and small fish. The taxon Odontoceti contains whales, dolphins and porpoises, all of which are toothed. The main difference between a toothed whale and a dolphin is size. Large toothed whales such as the sperm whale are considerably bigger than dolphins such as the common bottlenose dolphin or killer whale. The term dolphin means beaked and dolphin have a beak-like snout, whereas toothed whales do not. Porpoises tend to be smaller than dolphins, with a less prominent and more triangular dorsal fin compared to a dolphin’s more curved or wave-shaped dorsal fin. Dolphin teeth are cone-shaped while porpoise teeth are flat and spade shaped.

Table of the main differences between Odontoceti and Mysticeti

Characteristic Odontoceti Mysticeti
Feeding Echolocation, fast Filter feeder, slower
Size Smaller (except sperm & beaked whales) Larger (except pygmy right whale)
Blowhole One Two
Dentition Teeth Baleen plates
Melon Ovoid, in anterior facial region Vestigial or none
Skull and facial tissue Dorsally asymmetric Symmetric
Sexual dimorphism Some species have larger males Females always larger
Mandible Symphyseal (fused anteriorly) Non-symphyseal
Pan bone of lower jaw Yes No
Maxillae projection Outward over expanded supraorbital processes Under eye orbit, with bony protuberance anterior to eye orbit
Olfactory nerve and bulb Absent Vestigial
Periotic bone External to skull, fused with tympanic bulla Fused with skull

The habitat and range of cetaceans is varied and often unique to individual species. Cetaceans can be found in most marine environments from polar regions to temperate and tropical zones. There are also four species of non-marine river dolphins. Some species such as the river dolphins are restricted in their range to specific habitats, however other species traverse vast migrations through many different marine habitats. For example, some humpback whale populations migrate from cooler productive water in temperate zones where they feed, to warmer less productive tropical zones where they calf and breed. Still other species follow oceanic currents tracking prey, such as the Atlantic spotted dolphins. Locally occurring species within the Cayman Islands are largely transient, rarely coming close to shore; these species have a large range not restricted to the Caribbean. Exceptions may include species of beaked whales whose local range may be restricted to deep foraging water such as the Cayman trench.

Status

Distribution: In the Cayman Islands, cetaceans are found offshore, usually in small pods. Distributions of regionally occurring species are likely limited to pelagic environments, possibly with tendency toward brief stops at oceanic atolls and deep water trenches. Small mother and calf groups have been observed for several Odontoceti species which appear to have regional distributions limited only to pelagic environments.

Conservation: Recent local studies in the Cayman Islands have discovered that cetacean occurrences are brief and rare. The lack of frequent occurrences inshore of cetaceans is anomalous and warrants further investigation; however a likely reason for infrequent sightings may be noise pollution from heavy shipping traffic and a paucity of prey species. Relative abundances of occurring species are being estimated but are likely to be significantly lower than other regions within the wider Caribbean. The conservational status for cetaceans occurring in the Cayman Islands can be seen in the table below, descriptions are summarized from the IUCN Red List.

Legal status: there is currently no specific legal protection for cetaceans on a national scale.