The onepu is the largest living frog on Io. This species has a relatively small habitat range and are generally confined to Iokeihiko. Its numbers are dwindling due to habitat destruction, poaching, and sport hunting. Attempts to relocate onepu for conservation efforts have been widely unsuccessful.
Description
Distribution and habitat
Ecology and Behavior
Attacks on ‘credes
Description
Onepu grow to a length of up to 6 m (20 ft), rarely exceeding 6.3 m (21 ft) or a weight of 1,000–1,300 kg (2,200–2,900 lb). The sexes of the onepu are similar. Onepu eggs and tadpoles are about the same size as other frogs despite their very large adult form.
A lateral fold extends from the eye to the posterior portion of the tympanum. Toes are fully webbed, with large interdigital membranes extending down to the toe tips. The second toe is the longest. The skin on the dorsum and on top of the limbs is granular. Dorsal coloration is green sienna, while the abdomen and ventral part of the limbs are yellow/orange. They have acute hearing, but no vocal sac, and also lack nuptial pads.
Distribution and habitat
The river systems in which these frogs live are often found in dense, extremely humid areas with relatively high temperatures. These rivers are usually clear and highly oxygenated. Although generally staying in the rivers during the day, they often emerge on land during the night.
Because of its tendency to swim long distances at sea, individual onepu appeared occasionally in areas far away from their general range. Onepu generally spend the tropical wet season in freshwater swamps and rivers, moving downstream to estuaries in the dry season. Onepu compete fiercely with each other for territory, with dominant males in particular occupying the most eligible stretches of freshwater creeks and streams. Junior onepu are thus forced into marginal river systems and sometimes into the ocean. They can survive for prolonged periods in only warm temperatures, and onepu seasonally vacate parts of Iokeihiko if cold spells hit.
Ecology and Behavior
Like most amphibians, water is vital for their reproduction. Because the onepu lacks a vocal sac, it does not produce mating calls. The egg masses consist of several hundred eggs, and often attached to aquatic vegetation. There are three main nest types, all semi-circular in shape and located in or near a river: In the first they clear a section in a river pool. In the second they expand an already existing pool, damming it off from the river. In the final they dig a pool, roughly, sometimes moving quite large stones in the process. This may partially explain the onepu's large size, as larger frogs may be more successful at moving heavy objects when constructing their nests. Adults have also been shown to guard the nests at night. Although not confirmed, there are indications that the nest is constructed by the male, while the female guards the nest with the eggs. Larval development takes between 85 and 95 days.
The onepu is a large and opportunistic hypercarnivorous apex predator. It ambushes most of its prey and then drowns or swallows it whole. It is capable of prevailing over almost any animal that enters its territory, including other apex predators such as sharks, varieties of freshwater and saltwater fish including pelagic species, invertebrates such as crustaceans, various reptiles, birds and mammals, including ‘crede.
Attacks on ‘credes
Of all the animals on Iokeihiko, Onepu have the strongest tendencies to treat ‘credes as prey. The onepu has a long history of attacking ‘credes who unknowingly venture into its territory. As a result of its power, intimidating size and speed, survival of a direct predatory attack is unlikely if the onepu is able to make direct contact. The only recommended policy for dealing with onepu is to completely avoid their habitat whenever possible, as they are exceedingly aggressive when encroached upon.
Exact data on attacks are limited. However, claims in the past that onepu are responsible for thousands of ‘crede fatalities annually are likely to have been exaggerations and were probably falsified to benefit leather companies, hunting organizations and other sources which may have benefited from maximizing the negative perception of onepu for financial gain. Although it does not pay to underestimate such a formidable predator, wild onepu are normally quite wary of ‘credes and will go out of their way to submerge and swim away from them, even large adult males. Some attacks on ‘credes appear to be territorial rather than predatory in nature, with onepu over two years in age often attacking anything that comes into their area (including boats). ‘credes can usually escape alive from such encounters, which comprise about half of all attacks.
In 1262, a 600-strong mob slaughtered 163 onepu in Iokeihiko in a revenge attack after a man was devoured. The incident was one of many that prompted the closure of Iokeihiko as a natural preserve.
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