Tuesday, 7 July 2020

Sympterichthys unipennis: Smooth Handfish declared extinct.

The Smooth Handfish, Sympterichthys unipennis, has officially been declared extinct by the International Union for Conservation of Nature, the first marine Fish to receive a formal determination of extinction. Determining the conservation statue of marine species is always difficult, making scientists reluctant to declare the extinction of modern species, but the highly endemic (localised) nature of Handfish populations, combined with the repeated failure of scientists to discover any survivors of the species over the past two decades, and the known environmental damage to the home range of the Smooth Handfish, has led to the conclusion that there are no surviving members of the species.

The only surviving specimen of the Smooth Handfish, Sympterichthys unipennis, in the collection of the Museum National d’Histoire Naturelle in Paris. Fishes of Australia.

Handfish, Brachionichthyidae, a form of Anglerfish, are highly unusual in that they are benthic (bottom-dwelling) for their entire life-cycle, moving over the seafloor by walking on leg-like fins. They lay their eggs on the seafloor, and the young, when they emerge are essentially miniature versions of the adults, with an identical form of locomotion. Individual species tend to have very specific habitat requirements and limited distributions, with most species having very few populations. All of this combines to make these Fish unusually vulnerable to extinction, and also to make such extinctions detectable to scientists.

The estimated original range of the Smooth Handfish, Sympterichthys unipennis. Fishes of Australia.

The only known specimen of the Smooth Handfish is in the collection of the Museum National d’Histoire Naturelle in Paris. It was collected by French zoologist François Péron during Nicolas Baudin's expedition to Australia from 1801-1804 aboard the ships Géographe and Naturaliste. The specimen was collected from the southeast coast of Tasmania, probably the D’Entrecasteaux Channel. The simple dip-net technology used by Péron suggests that the species was fairly numerous and therefore easily caught. Péron's specimen was formally described by the French zoologist Georges Cuvier in 1817, under the name Chironectes unipennis. The species has never been encountered again.

Illustration of 'Chironectes' unipennis from Cuvier's original 1817 description of the species. Fishes of Australia.

The D’Entrecasteaux Channel is known to have been the area of an extensive Scallop and Oyster fishery from the late nineteenth century until 1967, when the industry collapsed due to overfishing. During this period shellfish were dredged from the channel, a practice in which a bar is dragged across the sediment in order to disturb the target species, with a net behind to capture them. This practice is often highly destructive to the environment, and typically produces a significant amount of bycatch (species which are not targetted, and which are subsequently disgarded by the fishermen). It is thought that every part of the D’Entrecasteaux Channel was dredged in the nineteenth and twentieth centuries, and that this probably wiped out the Smooth Handfish.

An illustration of a shellfish dredge from 1873-4. Popular Science Monthly Volume 6/Wikimedia Commons.

During the past two decades extesive surveys of Handfish off the coast of Tasmania have been made by SCUBA divers, in order to monitor the populations of three other endemic species, the Red Handfish, Thymichthys politus, Ziebell's Handfish, Brachiopsilus ziebelli, and Spotted Handfish, Brachionichthys hirsutus, all of which are currently classed as Critically Endangered under the terms of the  International Union for the Conservation of Nature’s Red List of  Threatened Species. During this time no trace of the Smooth Handfish has been made, leading to the conclusion that the species has become extinct at some time since it was last encountered at the beginning of the nineteenth century.

A Critically Endangered Ziebell's Handfish, Brachiopsilus ziebelli, off the eoutheast coast of Australia. Red List of Threatened Species.

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