An assessment of parasite infestation rates of juvenile sockeye salmon after 50 years of climate warming in southwest Alaska

Climate change has produced disproportionate levels of warming in high latitude ecosystems. A critical challenge is to understand how changes in temperature will mediate ecological processes, such as disease. Several authors have suggested that warming will increase prevalence of diseases at high latitudes, yet long-term studies are lacking. We evaluated how parasite abundance and prevalence in an ecologically and economically important species (juvenile sockeye salmon Oncorhynchus nerka) has changed in an Alaskan watershed that has experienced substantial climatic change over the past half-century. We hypothesized that the average increase in summer water temperature of 1.9°C over the past 46 years in our study system would have resulted in a corresponding increase in fish metabolism, and thus potential consumption rates, that would increase infestation rates of the tapeworm Triaenophorus crassus. However, our comparison of data from 1948–1960 to 2008–2009 provided no evidence that the parasite load in juvenile sockeye salmon has significantly changed and that there is no significant relationship between summer temperature and average infestation rates. Climatic projections for southwest Alaska forecast a continuation of the current warming trend, which could potentially have effects on our studied parasite-host interaction, but thus far we found no change in infestation rates over the last 60 years.