Errors associated with otter Lutra lutra faecal analysis. II. Estimating prey size distribution from bones recovered in spraints

摘要: New methods of estimating the size salmonids Salmo spp. and eels Anguilla anguilla consumed by otters Lutra lutra are presented, based on feeding trials involving captive, tame otters. These involve modelling size-related differential recovery key fish bones recovered in faeces (spraints) avoid two sources errors that may have occurred using previous techniques which relied solely a series correlations between length individual vertebrae. Sources avoided are: (a) vertebrae spraints could not always be assigned to correct correlation equation for mean, maximum, or minimumsized bones; (b) number represented spraint was assumed one, case similarly-sized vertebrae, varying considerably size. We tested use salmonid atlas determine largest minimal numbers estimate, frequency distribution consumed, estimate proportions trout salmon diet. Eels do contain an is resistant digestion so equivalent estimates minimum possible. A model therefore developed lengths from thoracic equations. For each type prey (salmonids eels), identifiable recorded were related original ingested fish. Such models greatly enhance value otter analyses, particularly size-selection studies.