Effective waterbird deterrents for floating oyster farms: implications for water quality and Campylobacter presence

Floating oyster aquaculture gear offers roosting sites for waterbirds, which defecate on crops, potentially degrading water quality by introducing fecal coliforms and pathogens that pose human health risks, like pathogenic Campylobacter spp. (e.g. C. jejuni, C. lari, C. col i ). We evaluated the effectiveness of bird deterrents in reducing waterbird density and examined whether bird density was associated with fecal coliform concentrations in water and oyster meat, as well as with the presence of pathogenic Campylobacter spp. in oyster meat. From 3 July to 13 November 2024, we conducted weekly waterbird surveys at 6 floating farms in New England (USA) to compare waterbird densities between areas of farms with and without deterrents. We concurrently sampled water (n = 212 samples), bird feces (n = 123), and oysters (n = 112). The most common waterbird species observed on farms were common tern Sterna hirundo (n = 2660), herring gull Larus argentatus (n = 1599), double-crested cormorant Nannopterum auritum (n = 1089), laughing gull Leucophaeus atricilla (n = 761), common eider Somateria mollissima (n = 88), and great black-backed gull Larus marinus (n = 59). We found that waterbird density was higher (β = 3.29, credible interval = 2.41-4.19) on farm sections without deterrents; however, density was not associated with fecal coliform levels in water or oyster meat, nor with the presence of Campylobacter spp. in oyster meat. Only 3 fecal samples tested positive for Campylobacter spp. Our research suggests that waterbird feces are not the sole cause of water quality degradation or Campylobacter outbreaks on oyster farms.