Impact of organochlorine pesticide residues and PCBs on otters (Lutra lutra) in eastern England.

A study of otter (Lutra lutra) populations and levels of organochlorine (OC) pesticide residues and PCBs in otter faeces (spraints) was made on rivers in East Anglia, England. Population and contaminant levels are compared against target values. It is thought that the native otter population was almost extirpated during the study period. The current population must derive largely, if not entirely, from captive-bred animals introduced since 1983. Its range has expanded little and population levels, measured as an index, were generally low. Concentrations of OC pesticides and PCBs were similar to those of lowland stretches of western rivers; however, samples had a smaller proportion of dieldrin and a greater proportion of PCBs. Overall 44% of samples had concentrations of contaminants exceeding the 'level of concern'. It is considered that contamination, especially by PCBs, remains a factor influencing otter populations, which may not be viable in East Anglia without repeated releases of captive-bred animals.