Individual study: A comparison of the efficiency of live cage-traps set on different sized rafts in the capture of feral coypu Myocastor coypus in the Yare and Chet River Valleys, Norfolk, England
Baker S.J. & Clarke C.N. (1988) Cage trapping coypus (Myocastor coypus) on baited rafts. Journal of Applied Ecology, 25, 41-48
Feral populations of coypu Myocastor coypus (a large rodent native to South America) exist in many countries and a number of different control methods are employed. In Britain (where there were formerly feral populations of coypus established in wetlands in eastern England through individuals escaping from fur farms), it is illegal to use spring traps or poison against coypus, and trappers use cage traps to catch and hold coypus until they can be humanely killed. The experiment reported here compared the efficacy of cage trapping where cages were set on baited rafts of two different sizes.
Study area: Trapping was carried out between March and June 1983 by experienced trappers in a 1,100 ha area of the Yare River Valley (the same as that trapped during winter of 198 1-82) with the addition of an adjoining 3 km of valley along the River Chet, Norfolk, eastern England. The land is a flat patchwork of pasture and arable fields intersected by drainage ditches, and at this time supported a feral population of coypus.
Rafts: Rafts of two types were used. A larger raft ('large raft' - 20 kg each and comprised a 2 m x 1 m plywood base, with blocks of expanded polystyrene fixed underneath to provide additional buoyancy) which was the type used in the comparison with land traps (see: www.conservationevidence.com/ViewEntry.asp?ID=826 for summary). The other type was of similar design but smaller ('small raft'): 1.5 m x 0.6 m, holding two traps (as opposed to three) and weighing 6.5 kg.
Trapping procedure: Eight large and eight small rafts were randomly allocated amongst 16 selected trapping positions. Trapping was carried out for 5 weeks, after which the rafts were withdrawn. They were returned 2 weeks later for a further 5 weeks, with the positions of large and small rafts reversed.
Over the trapping period, 28 coypus were caught on large rafts and 23 on the smaller ones (this was not statistically significantly different). Captures were made at 12 widely scattered raft positions.
Although the small rafts were relatively unstable, they were as successful as the large ones as a platform for traps and the compact design was readily accepted by ‘Coypu Control’ trappers as they were more easy to transport and install.
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