Indications that algal blooms may affect wild salmon in a similar way as farmed salmon

Abstract

Based on a four year study conducted in Cowichan Bay, Canada, potential linkages between composition and abundance of phytoplankton and the feeding and histopathology of juvenile salmon were noted. During two dense blooms (Skeletonema spp. and Pseudo-nitzschia spp.), feeding of juvenile Chinook salmon decreased (n=202, empty stomachs >50%). All collected salmon gills (n=5) were damaged following high levels of mechanically harmful Chaetoceros convolutus in the water column; all collected livers (n=5) showed signs of pathological changes during Octactis speculum bloom. These observations were consistent with effects previously reported from salmon farms, however this agreement must be treated with caution as it is based on a limited number of samples. We suggest that there is a need for comprehensive studies to evaluate the potential role of harmful algae as a stressor to wild fish in a coastal environment.