Individual study: Introduction of feline panleucopaenia successfully controls feral cats Felis catus, on Marion Island, South Africa
van Rensburg P.J.J., Skinner J. D. & van Aarde R. J. (1987) Effects of feline panleucopaenia on the population characteristics of feral cats on Marion Island. Journal of Applied Ecology, 24, 63-73
In common with many other oceanic islands, introduced species have decimated Marion Island's flora and fauna. Mice arrived with 19th century seal hunters, damaging plant and insect life, and the five cats Felis catus introduced to control them in 1949 had multiplied to 3,400 by 1977, and had devastating effects on ground-nesting bird populations. By 1975 cats were killing some 450,000 petrels (Procellariidae) each year and measures to control cats were therefore considered necessary. This study evaluated the effects of the artificial introduction of feline panleucopaenia (FPL) as a control measure of the feral cat population on this sub-Antarctic island.
Study area: Marion Island (46"54'S, 37'45'E) is a 290 km² sub-Antarctic island lying in the Southern Indian Ocean approximately 1,770 km south east of Port Elizabeth, South Africa. It is of volcanic origin with a tundra flora.
Cat control: In order to control the susceptible and isolated population of cats which were decimating populations of ground-nesting birds, feline parvo virus was introduced during 1977in an attempt to create an epidemic of the disease feline panleucopaenia (FPL).
Cat population monitoring: Characteristics for the 1982 cat population were derived from material and information obtained between April 1981 and May 1983. Density and population estimates were extrapolated from data collected in a study area of 32.8 km², which was stratified into a coastal (0-100 m a.s.1.) and an interior zone (100-450 m a.s.l.), and divided into 0.67 km² grid blocks. The area was surveyed on foot at monthly intervals and individual cat identification was based on coat colour patterns and body size.
Between December 198 1 and March 1983, 258 cat sightings were made, 134 of these represented 104 different individuals within the defined study area. The cat population decreased from an estimated 3,409 cats in 1977 (at introduction of feline parvo virus) to 615 (S.E. =107) by 1982, giving an annual rate of decrease of 29%.
Litter size also decreased (litter size at weaning decreased from 2.66 in 1975 to 1.65 in 1982) and the age structure changed significantly because of a decrease in subadult numbers. Age specific mortality rates were higher but followed the same pattern as in 1975 because there were fewer subadults but the same age structure of adults.
Antibody titres of FPL were lower in 1982 than in 1978 which illustrates that FPL affected the cat population but was no longer spreading effectively
Conclusions: The introduction of a virulent strain of feline parvo virus was successful in dramatically reducing the feral cat population on Marion Island. The decrease of 29%/ year over 5 years (1977-82) as compared to 8%/year over the fieldwork period (1981-82 to 1982-83) suggests that the population may be stabilizing. This observation was supported by lower FPL titres. Lowered fecundity, a drastic decrease in density, a change in the age structure and a decrease in growth indicate that FPL can be usedeffectively as a biological control measure to reduce the density of susceptible cat populations as part of an effort either to control or to eliminate such populations.
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