Parasitic Infestation and Temperature Change
It has been assumed that transmission rates of parasites and pathogens can be expected to increase with rising temperature, but Authors Bentley and Burgner proved otherwise in a 2011 study of juvenile sockeye salmon (Oncorhynchus nerka) in the Alaskan watershed, which had experienced a 1.9°C increase in summer water temperature over the prior 46 years. The researchers compared infestation rate data for the tapeworm Triaenophorus crassus collected between 1948 and 1960 with similar data obtained in 2008 and 2009 from the Wood River system of Bristol Bay, Alaska. Comparing the average summer air temperature to the parasite prevalence of juvenile sockeye salmon, Bentley and Burgner found “no significant relationship over the fifteen years of collected data," and when they compared the 13 years of historic parasite prevalence to equivalent data collected in 2008 and 2009, they did not find a statistically significant positive long-term trend. The authors say that their data demonstrate that "the complex effects of warming have not summed to generate a measurable change in the infestation rates of juvenile sockeye salmon in the Wood River system."
Bentley, K.T. and Burgner, R.L. 2011. An assessment of parasite infestation rates of juvenile sockeye salmon after 50 years of climate warming in southwest Alaska. Environmental Biology of Fishes 92: 267-273.