Upper Thermal Tolerance of Mountain Whitefish Eggs and Fry

Abstract

Some populations of Mountain Whitefish Prosopium williamsoni, a widely distributed native Rocky Mountain salmonid, have experienced catastrophic declines while other populations remain robust. To assess the possibility that the declines have arisen from climate‐related factors, several experiments were conducted to determine the upper thermal tolerances of embryos and fry and the effects of temperature on growth. Hatching of eggs was measured at 5.7, 6.4, 8.4, and 10.4°C (three replicates each). Survival and growth of fry were measured for 33 d at 5.7, 8.2, 11.8, 16.5, 19.1, 22.2, and 25.2°C (three replicates each). Mean hatching success was 96.7% (SD, 2.9) at 5.7°C, 98.3% (2.9) at 6.4°C, 90.0% (8.7) at 8.4°C and 38.3% (10.4) at 10.4°C. The ultimate upper incipient lethal temperature for fry was 23.6°C (95% CI, 23.5–23.7°C) after 7 d, which decreased with time to 22.6°C (22.1–23.0°C) after 33 d. The critical thermal maximum was 26.7°C (SD, 0.8) for fry acclimated to 13.4°C. The temperature for maximum growth was 13.8°C (95% CI, 10.8–16.8°C). Growth rates above and below the temperature for maximum growth decreased sharply to about 40% of the maximum at 5.7°C and 22.2°C. Based on these experimental data, the criteria for the protection of Mountain Whitefish fry are 21.6°C for acute water temperature and 16.8°C for chronic water temperature. The acute criterion for reproduction—based on the maximum temperature for successful incubation—is 8.4°C. The low upper thermal tolerance of Mountain Whitefish relative to those of other salmonids suggests that they will be very vulnerable to the increasing stream temperatures resulting from climate change.

Spatiotemporal patterns of mountain whitefish (Prosopium williamsoni) in response to a restoration of longitudinal connectivity

“…maximum growth rate occurred at 13.8°C), a sensitivity which may contribute to recent population declines in portions of their range (Brinkman, Crockett, & Rogers, 2013). Research on the effects of water temperature on mountain whitefish is sparse and generally inconclusive; however, a recent experiment focusing on early life stages showed mountain whitefish were sensitive to warm thermal regimes (e.g.…”

“…Research on the effects of water temperature on mountain whitefish is sparse and generally inconclusive; however, a recent experiment focusing on early life stages showed mountain whitefish were sensitive to warm thermal regimes (e.g. maximum growth rate occurred at 13.8°C), a sensitivity which may contribute to recent population declines in portions of their range (Brinkman, Crockett, & Rogers, 2013).…”

Reproductive Ecology, Spawning Behavior, and Juvenile Distribution of Mountain Whitefish in the Madison River, Montana

“…Weekly movement rates for females and males are offset and are for the week starting with the date labeled on the axis. On temperature plots, horizontal lines indicate thermal thresholds for successful embryo development (9°C = maximum, 6°C = upper optimal; Rajagopal 1979;Brinkman et al 2013).…”

“…The exact mechanisms for declines are often unknown. Studies have documented mechanisms of Mountain Whitefish mortality including whirling disease (Schisler 2010;Pierce et al 2012), high temperatures (Boyd 2008;Brinkman et al 2013), pollutants (Brinkman et al 2008;Quinn et al 2010), decreased discharge, and entrainment (Kennedy 2009). However, little is known about the effects of these stressors on populations (but see IDFG 2007; Kennedy 2009).…”

When Do Mountain Whitefish (Prosopium williamsoni) Spawn? A Comparison of Estimates Based on Gonadosomatic Indices and Spawner and Egg Counts

“…Historically, Mountain Whitefish have not been as extensively studied as other native western salmonids, perhaps due to their lack of popularity as a sport fish and their perceived robust abundance [4]. However, more recent investigations on Mountain Whitefish have illustrated their sensitivity to changes in lotic environments from impoundment [5] and highlighted significant declines in at least some parts of their range [6,7]. Causal mechanisms for the declining Mountain Whitefish populations remain unknown but are coincident with modified water flows, increased water temperatures, altered disease incidence and increased anthropogenic disturbances [5 -7].…”