Study of the bacterial content of ring-billed gull droppings in relation to recreational water quality

Abstract Ring-billed gull populations of eastern North America have grown dramatically in the past 30 years. To assess the possible impact of these populations on recreational waters, gull droppings collected at three colonies were examined for fecal coliforms, Aeromonas spp., Campylobacter spp., Pseudomonas aeruginosa, Salmonella spp. and Staphylococcus aureus . The samples were also analyzed for Shigella spp. and Yersinia spp. The samples were collected every two weeks from late April to mid-July. The measured concentrations were compared on the basis of colony, age class and sampling date by analysis of variance (ANOVA) and Fisher’s LSD multiple range test. In general, there was little difference in bacterial content as a function of age groups, colony or sampling date. On the basis of the documented ratios between the various pathogens and total coliforms in the droppings, the limit of 200 fecal coliforms per 100 ml of water used for recreational water quality in Canada provides an acceptable level of protection with respect to contamination by gulls. However, we must qualify these findings by stating that they reflect the situation that existed at the time of sampling, that they apply to a small number of pathogenic microorganisms, and that they do not take into account soil or sand contamination at beaches.