Population structure of coypus (Myocastor coypus) in their region of origin and comparison with introduced populations

Abstract

The first population recapture study of indigenous coypus Myocastor coypus is reported in protected areas of Argentine pampas within a region where the species is hunted for food and fur. Quarterly live trapping at two sites captured a high proportion of all coypus present (96% of juveniles; 85% of adults, independently of season, site and sex). Survival (from mortality or emigration) was constant across sites and seasons, and higher for juvenile males than females (88% and 71%, respectively) and lower for adult males than females (45% and 81%). Most turn-over in numbers was replaced by births, and immigrating males tended to be the largest individuals present. Sex ratios were male-biased amongst juveniles and female-biased amongst adults. Taken together, these results are consistent with local resource competition in habitat rendered low in quality by crowding inside the locally protected areas. The indigenous coypu population matured more slowly, and to a smaller maximum body size, than coypus studied in introduced populations in North America and particularly in northern Europe. Cold European winters may have contributed to the evolution of precocious sexual maturity and larger body sizes in European compared with indigenous populations.

Population parameters of indigenous populations ofMyocastor coypus: the effect of hunting pressure

“…The persistence of these populations was probably due to dispersing individuals. Our results indicate that hunting pressure may modify the structure of coypu populations that otherwise inhabit a relatively stable environment (Guichón et al 2003c). In the pampas region, one of the main features determining landscape heterogeneity for coypus is the spatial variation in hunting pressure.…”

“…A total of 87 individuals was identified at Ruiz, 55 at Jáuregui, 14 at Luján, and 10 at Ratti. The minimum number alive (MNA) provided a good estimator of coypu abundance on the basis of a high and constant recapture probability predicted by Cormack-Jolly-Seber models at Ruiz and Jáuregui (Guichón et al 2003c). We were unable to use these models at Luján and Ratti due to the low number of animals.…”

“…Survival rate was estimated as the number of marked animals that were captured in one season divided by the total number of marked animals in the previous trapping session (Pollock et al 1990); therefore, population losses (1 -survival) included emigration and mortality. Individuals first captured with a body weight < 1.5 kg were most likely offspring born on the site between trapping sessions, based on Brown (1975: juveniles weighed < 1.25 kg) and our recapture data (juveniles of 0.2-1.5 kg at first capture weighed 1.1-2.5 kg when recaptured while no new coypus of 1.5-2 kg were trapped); other first captures were assumed to be immigrants (Guichón et al 2003c). Immigration rate was calculated as the number of immigrants divided by the total number of immigrants and residents in each season at each site.…”

Reproductive biology of the coypu, Myocastor coypus (Rodentia: Myocastoridae) in western Japan

“…Our results show that, in western Japan, the coypu may reach sexual maturity at 4-6 months of age, regardless of sex, similar to the age of maturity of other introduced populations in the USA (ATWOOD 1950, WILLNER et al 1979), England (GOS-LING 1974, LAURIE 1946, NEWSON 1966), and Italy (COCCHI & RIGA 2008, and less than that of indigenous population in Argentina (males: 8-11 months; females: 5-10 months) (GUICHÓN et al 2003). PURVIS et al (2001) suggested that sustainable harvesting of wildlife populations should exert a strong selective force for earlier maturity.…”

A mortality survey of free range nutria (Myocastor coypus)

“…Predation is a serious problem for nutria in those areas with the presence of stray dogs, like regions 1 and 3; meanwhile coypus road kill is clearly another threat, as traffic on most roads moves as fast as 70 miles/h. Nevertheless, our figures for road kills seems to be high based on the restricted use of space by coypus, which are rarely observed more than 10 m from the water's edge (Guichon et al 2003). Apparently, debilitated coypus are prone to be attacked by carnivores or to miscellanea trauma.…”