
Thursday 15 February
The World's Favourite Unloved Species 2018 - the Galapagos Racer
Kingdom | Animalia |
Phylum | Chordata |
Class | Mammalia |
Order | Cetartiodactyla |
Family | Delphinidae |
Genus | Peponocephala (1) |
The melon-headed whale (Peponocephala electra) is a member of a group of small, dark-coloured whales often referred to as ‘blackfish’ (5). As this name suggests, this whale is a black or dark-grey colour, although the lips are a starkly contrasting white and the undersides are pale grey (2) (5). A distinct dark eye patch broadens around the face, giving this whale the appearance of wearing a mask, while a faint light band extends from the blow hole to the rounded melon (2) (5). The body is long and slim, with a proportionately long tail and, lacking a beak, the forehead curves smoothly from the tip of the nose to the blowhole. The male is larger than the female and has a taller dorsal fin, and the pointed, tapering flippers are comparatively longer (5) (6). The melon-headed whale is very similar in appearance to the closely related pygmy killer whale (Feresa attenuate), but may be distinguished by its more triangular head-shape, more pointed flippers, and the possession of substantially more teeth, of which it has between 20 to 26 on each side of both jaws (3).
When swimming at speed, the melon-headed whale makes shallow leaps out off the water, creating huge amounts of spray. Slower moving individuals may be seen to lift the entire head out of the water when surfacing, and occasionally this species will spyhop, a behaviour where the whale rises and holds its position partially out off the water, exposing the underside of its head (8).
Like many other cetaceans, the melon-headed whale is a highly social animal and typically travels in large groups of several hundred, although up to 2,000 individuals have been seen travelling together (7). Within the pod, the whales are tightly packed and make frequent and rapid changes in direction (8). This species often associates with other cetaceans, and is often seen following or at the edge of groups of Fraser’s dolphin (Lagenodelphis hosei) (6) (7). Strong social bonds are formed between whales, and within large pods smaller groups may cooperate together when feeding (6) (7).
This whale feeds on a variety of pelagic fish and squid, although it may also supplement this diet with crustaceans (7). It is likely that it feeds deep in the water column and drives its prey upwards, trapping it at the water’s surface (7). The timing of breeding is unknown, but may peak between August and December in the southern hemisphere, and between July and August elsewhere (3) (8). As is typical of most small cetaceans, the young calves are born after a one year gestation period, and male melon-headed whales have a lifespan of 22 years, while the females may live to 30 years of age (6) (7).
Due to its large range and population, currently estimated at over 50,000, of which around 45,000 reside in the tropical east Pacific, the melon-headed whale is not thought to be threatened with extinction. This species is relatively common in parts of its range, in particular in the Philippine Sea, which is perhaps the species’ stronghold. However, at present there is no information available on population trends, and as its fish prey is likely decreasing from over-fishing, this whale may actually be in decline (1).
The melon-headed whale is taken in a number of small net and harpoon cetacean fisheries, including in St Vincent, the Philippines and Taiwan, while it is also killed in the annual dolphin drive at Taiji, Japan, although the number of whales killed in these fisheries and its impact on the population is unknown (1). A small number of whales are also killed as bycatch in nets for tuna, although this is likely to be a somewhat smaller threat compared to direct fishing (1) (5).
Mass strandings of the melon-headed whale are commonly reported which, although the cause of this is unknown, may be due to outbreaks of parasites or a panic response in the school when a few members accidentally become stranded (5). However, one incident on the Hawaiian island of Kauai, when between 150 and 200 whales become stranded on a bay, may be attributed to U.S. Navy training involving the use of sonar (1) (8). It is also possible that the use of sonar and seismic exploration can kill whales by causing gas bubble disease (9).
The melon-headed whale could also become threatened by climate change, as rising sea levels and increased surface sea temperatures may potentially alter the abundance and distribution of its prey species (10).
The melon-headed whale is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that international trade in this species should be carefully monitored (4). There is still very little know about this species, partly due to its relative unimportance as a commercial species and offshore habits, and further research is required if the uncertainty surrounding the significance of the threats to this species is to be resolved (1) (6).
For more information on the melon-headed whale:
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Thursday 15 February
The World's Favourite Unloved Species 2018 - the Galapagos Racer
Thursday 01 February
Thursday 01 February