Organochlorine Residue Levels and Bioconcentration Factors in Otters ( Lutra lutra L.) from Northeast Spain

Abstract

The dramatic reduction observed in the distribution of the Eurasian otter (Lutralutra ) during the latter half of this century has been largely attributed to pollution(MacDonald, 1991). Attention has focused on organochlorine compounds, inparticular PCB (Mason 1989; Olsson and Sandegren 1991; MacDonald and Mason1992). The scarcity of the otter, and protection afforded, has meant tissue samplesare difficult to obtain and has led to fish, the principal prey, being used in manystudies (Hider et al. 1982; Olsson and Sandegren 1991; Smit and de Jongh 1991).Studies combining both otter and fish tissue samples from the same location,however, are rare (Foley et al. 1988; Smit and de Jongh 1991) due primarily tothe difficulty of obtaining samples of this mustelid. Bioconcentration factors ofthese pollutants have not, therefore, usually been calculated for this species in thewild. To address this shortcoming fish were analyzed from sites where ottersamples were taken. Fish constitute between 95-100 % of the otter’s diet in thearea of study (Ruiz-Olmo 1995). This area is constituted by three rivers(Noguera Ribagorzana, Noguera Pallaresa and Segre) where live the last otterpopulations in Catalonia (Ruiz-Olmo 1995). These populations are completelyisolated by unsurmountable dams built in narrow gorges.The bioconcentration factors thus obtained allow theoretical concentrations of thesecompounds in otter tissues to be calculated from the mean levels found in fish:MATERIALS AND METHODSSix otters were found dead by different causes: road-traffic accident (4), hunted(1) and mother killed (1), in the N.E. Spain between 1988 and 1993. The corpseswere frozen at -20 °C until post-morten analysis. Each specimen was sexed (4males and 2 females), measured and removed the canine tooth to age (2 of 0+, and 1of 1+, 2+, 4+ and 6+ year category). Tissue samples from the leg muscle andliver were removed for organochlorine analysis. These data are included in anotherfuller study about the otter pollution in Spain (Ruiz-Olmo et al. in press). Fish,captured using electro-fishing, were taken from the stretch of the river (0-15km.) where the otters had been found. These were also frozen until the analysiswhen the weight and length were measured (Table 1). Fish tail muscle was used forchemical analysis.The samples were analyzed using gas chromatography, followingthe method described by Lopez-Martin et al. (1994).