Temporal Trends in Sea Lice Infestation Pressure on Wild Fish

In 2012, baseline research characterized infestations of sea lice on wild fishes of Cobscook Bay, Maine (USA), a region with Atlantic salmon Salmo salar aquaculture.  Caligus elongatus was the only identified sea lice species and was observed on 10 fish species.  The high abundance and infestation pressure on threespine sticklebacks Gasterosteus aculeatus allowed a preliminary assessment of trends in infestation pressure. Peak infestation intensity (2 sea lice / fish) and prevalence (27%) were observed in June, raising questions about sea lice dynamics.  Similar sampling was therefore undertaken in 2013 to further examine sea lice dynamics on threespine sticklebacks in particular.  A total of 962 fish were examined for sea lice between May and November.  Again, only C. elongatus was identified on threespine sticklebacks at an overall infestation prevalence of 17%.  In both 2012 and 2013, no spatial trends were apparent among sampling sites, but peaks in infestation pressure occurred in early summer (May - June) and late fall (November).  These results indicate the presence of stable temporal trends in C. elongatus infestation pressure.  To date, potential reservoir hosts within the wild fish community of Cobscook Bay for Lepeophtheirus salmonis have yet to be identified.