Parasite Infestation of Young Sockeye Salmon in a Warming World
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.
Studying juvenile sockeye salmon (Oncorhynchus nerka) in an Alaskan watershed that had experienced a 1.9°C increase in summer water temperature over the prior 46 years, Bentley and Burgner hypothesized that the warming of the region "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." The set of events and their envisioned interaction seemed quite logical, so they proceeded to test their hypothesis by comparing infestation rate data for T. crassus collected between 1948 and 1960 with similar data obtained in 2008 and 2009 from the Wood River system of Bristol Bay, Alaska. And what did they find?
In the words of the two U.S. researchers from the University of Washington's School of Aquatic and Fishery Sciences:  "comparing the average summer air temperature to the parasite prevalence of juvenile sockeye salmon, we found no significant relationship over the fifteen years of collected data," [2,3] "evaluating the influence of average summer air temperature on the parasite infestation rates of juvenile sockeye salmon, we again found no significant relationship for either parasite abundance or parasite intensity,"  "when we compared the 13 years of historic parasite prevalence to equivalent data collected in 2008 and 2009, we did not find a statistically significant positive long-term trend in the data,"  "the parasite abundance of examined sockeye salmon smolts also did not exhibit a statistically significant long-term trend using the eight years of historic data and the two years of contemporary data," and, finally,  "evaluating the relationship between time and parasite intensity produced similar results as the other five comparisons, with there not being a statistically significant positive relationship."
In the concluding sentence of their paper, Bentley and Burgner say 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." And perhaps they never will; such is life in the real world.