Alien mammals, impact and management in the French subantarctic islands

Published source details Chapuis J.L., Boussès P. & Barnaud G. (1994) Alien mammals, impact and management in the French subantarctic islands. Biological Conservation, 67, 97-104.
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Summary

Native plant and animal communities of the French subantarctic islands of Saint-Paul (7 km²), Amsterdam (55 km²), Crozet archipelago (357 km²) and the Kerguelens (7,200 km²) have been greatly modified by introduced mammals. These islands are characterized by relatively low ecological diversity but are very important for some taxa (e.g. seabirds, for nesting). Nine introduced mammal species persist, cat Felis catus, European rabbit Oryctolagus cuniculus, cattle Bos taurus, reindeer Rangifer tarandus, sheep Ovis aries, mouflon O.ammon, house mouse Mus musculus, black rat Rattus rattus and brown rat R.norvegicus).

A review of the management of feral cats, rabbits and the four ungulates (published and unpublished data describing past, existing and planned control programmes) was undertaken. The three rodents (present at low density) were not considered in this review. Distribution by island (and introduction date) of present populations are:

Amsterdam: cats (1931); cattle (1871);

Crozet: cats (before 1887), rabbits (before 1887) on Cochons; rabbits (after 1826) on Est;

Kerguelens: cats (1956) on Grande Terre and Guiilou; rabbits (1874) on Grande Terre and eight smaller islands; reindeer (1955-1956) Grande Terre, and subsequently Foch; sheep (1952) on Longue and Moules; mouflon (1957) on Haute;

Saint-Paul: rabbits (after 1874).

Cats: Cats have reduced bird populations and diversity. Cat control (shooting) began on Grande Terre in 1960, resulting in near-eradication. However, the population recovered. Shooting was reinstated (1971-1977) reducing numbers from around 7,500 in 1973 to 3,500 in 1977. It was estimated that 3,500 cats killed 1.2-1.3 million birds annually. After 1977, numbers increased again (c.10,000 in 1984). New control measures are being considered.

Despite presence on Cochons (in 1974 c.300-400 individuals) and Amsterdam (low population density) contributing to extirpation or reduction of several bird species, no (documented) control measures have been undertaken.

Rabbits: On Grande Terre, rabbits were inoculated with myxomatosis virus in 1955 and 1956, and the population declined significantly in the 1960s. However, 12 years after virus introduction populations stablised. Monitoring at two sites (1983 and 1988) showed that myxomatosis killed only 1-8% of rabbits; the disease now plays only a minor role in regulating rabbit numbers.

Sheep: On Kerguelens in 1991, numbers greatly exceeded food requirements for research station staff; a flock of about 150 considered sufficient, suggesting removal of about 2,800 animals. A control programme is planned from January 1994.

Mouflon: On Haute since the 1970s to 1988, mouflon were shot annually for sport. During the 1988 autumn-winter, at least 106 were shot (225-300 starved). Between January and October 1988, the population approximately halved (in December 1988, 5-10 adult males for about 150 females). In 1994, control to reduce density to prevent further habitat degradation, or eradication is being considered.

Reindeer: On Grande Terre, 10-20 per year have been shot during the last decade. A recent observation on Foch suggests control may be needed.

Cattle: On Amsterdam cattle provide meat for station staff (60-120 slaughtered/year in the 1960s). Increasing numbers resulted in habitat degradation becoming 'alarming' in the 1980s. Cattle in the island's south were isolated by a 4 km fence in 1987. Over 900 were shot in 1988 and about 100 in 1989; 300 starved in 1988 in the north of the island. In May 1992, numbers were reduced from 842 to 515. Eradication from southern Amsterdam to protect the native tree Phylica nitida has resulted in increases of alien grasses.

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