Klamath River Thermal Refuge Provides Juvenile Salmon Reduced Exposure to the Parasite Ceratonova shasta

Abstract

Salmon in the Klamath River of northern California contend with water temperatures that reach stressful and sometimes lethal levels during summer, forcing them to seek thermal refuge at coolwater tributary junctions. During migration, these fish also encounter a range of pathogens that affect their survival. A significant myxozoan parasite, Ceratonova shasta, causes enteronecrosis in salmon, and this disease increases in severity as temperature and parasite dose increase. In complementary laboratory and field studies, we examined how the use of a thermal refuge (an area at least 2°C colder than the main stem) affects progression of enteronecrosis in juvenile Chinook Salmon Oncorhynchus tshawytscha and Coho Salmon O. kisutch. We compared fish use, water temperature, and C. shasta concentration in a refuge at the Beaver Creek–Klamath River confluence during the summer in 2008 and 2010. Salmonid numbers ranged from 190 to 2,125, and temperatures were 2–8°C cooler than in the main stem. In June and July of 2008, parasite levels in the refuge were lower than in the main stem, where they exceeded 100 spores/L. In 2010, main‐stem parasite levels did not exceed 10 spores/L, and levels in the refuge were lower in June. In the laboratory, we compared the effect of fluctuating and constant temperature treatments on mortality rates of Chinook Salmon and Coho Salmon exposed to C. shasta. Under most experimental conditions, fluctuating temperature, within the range experienced by fish using thermal refuges (15.5–21°C), had no significant effect on disease progression compared with a constant midrange temperature (18.5°C) with equivalent degree‐day accumulation. We propose that in the Klamath River thermal refuges can function as disease refuges from enteronecrosis by (1) providing areas of decreased C. shasta exposure and/or (2) alleviating disease effects as a result of relatively lower water temperatures. The trend of increasing water temperatures suggests that juvenile salmon will rely even more on these critical habitats in the future.Received October 9, 2015; accepted February 25, 2016 Published online June 22, 2016

Longitudinal thermal heterogeneity in rivers and refugia for coldwater species: effects of scale and climate change

“…Stream animals can survive periods of stressfully warm (or cold) temperatures provided there are adequate and well-connected thermal refuges (Ebersole et al 2003a;Torgersen et al 1999). Use of a thermal refuge may reduce metabolic costs and susceptibility to pathogens or toxins (Chiaramonte et al 2016), and may be especially important to animals at the equatorial limit of their range, those migrating long distances, and those that inhabit marginally suitable habitat. Salmonids evolved in freshwater systems with abundant cold water (Beechie et al 2012;McCullough et al 2009); both juvenile and adult salmonids seek refuge in cooler areas when water becomes too warm (Dugdale et al 2015b;Keefer and Caudill 2015;Petty et al 2012;Sutton and Soto 2012).…”

Climate Change and Considerations for Fish Health and Fish Health Professionals

“…Altered environments, defined by new abiotic and biotic norms, may present novel fish-pathogen interactions and the potential for emerging infectious diseases. For example, favorable thermal habitats that provide refuge from pathogens may be lost due to climate change, resulting in increased incidence of disease (Chiaramonte et al 2016). Future conditions may further stress native fish and favor the introduction, establishment, and distribution of invasives (Hellmann et al 2008;Quiñones and Moyle 2014), collectively compounding the likelihood of naïve populations (both indigenous and introduced) encountering new and more virulent pathogens.…”

Fisheries escape, temperature, and infectious agents: multiple stressors impacting wild sockeye salmon spawning migrations

“…Thermal refuges may provide additional benefits to migrating salmon by also providing refuge from certain infectious agents (Chiaramonte et al, 2016).…”

“…Temperature is known to impact all infectious agents, and for a majority of Pacific salmon infectious agents, higher water temperatures are usually associated with faster development and replication to a certain extent (Noe and Dickerson, 1995;Crossin et al, 2008;Marcogliese, 2008;Bettge et al, 2009;Ray et al, 2012;Chiaramonte, 2013). Warming water temperature may therefore be increasing RIB in fish (Chapter 5), and thermal refuges might be increasingly important for improving survival or recovery for fish with high infectious agent burden (Chapter 2), in addition to providing refuge from certain infectious agents (Chiaramonte et al, 2016).…”

“…This thesis also reports the novel findings of behavioural thermoregulation in response to fisheries interactions and high relative infection burden (RIB). Behavioural thermoregulation is being increasingly recognised for its benefits to salmonid survival (Newell and Quinn, 2005;Mathes et al, 2009;Keefer and Caudill, 2015), spawning success (Minke-Martin et al, 2018), injury and stress recovery (Bass, 2018; Chapter 2), and mitigating infection (Mathes et al, 2009;Chiaramonte, 2013;Chiaramonte et al, 2016;Chapter 3). As climate change persists, thermal refuges may be increasingly important for improving survival of salmon population.…”