Non-invasive Monitoring of Faecal Testosterone Metabolite Concentrations in a Northern Fur Seal (Callorhinus ursinus)

Abstract

We examined the relationship between serum testosterone and faecal testosterone metabolite levels in a captive northern fur seal (Callorhinus ursinus) using time-resolved fluoroimmunoassay to develop non-invasive testosterone monitoring technique. We found a significant relationship between faecal testosterone metabolite and serum testosterone levels when the faeces were collected approximately one day after blood withdrawal. In addition, faecal testosterone metabolite levels showed seasonal fluctuations that were similar to those found in serum testosterone levels, with higher testosterone levels occurring during the breeding season. These results indicate that serum testosterone levels can be estimated using faecal testosterone metabolite levels. These methods will be a useful tool to non-invasively monitor reproductive cycles of male northern fur seals.