Does habitat occupancy by lake trout and lake whitefish in large lakes match published thermal habitat envelopes?

Abstract

Habitat occupancy patterns of lake trout (Salvelinus namaycush) and lake whitefish (Coregonus clupeaformis) in two large Canadian Shield lakes were modelled based on detections of fish from repeated depth‐stratified surveys over several summers. Lake trout and lake whitefish consistently occupied sites outside traditional thermal envelopes and were not detected at some sites within these ranges. This included the metalimnion and shallow epilimnion for lake trout and lake whitefish in Lake Opeongo. Physical habitat covariates were not important in defining lake trout habitat in both lakes. Physical habitat as represented by the hardness/softness gradient based on acoustic substrate surveys was important for lake whitefish in Lake Opeongo but not in Smoke Lake. In addition, thermal envelopes for lake whitefish differed between the lakes possibly because of differences in substrate slope. The wash zone of lakes, where the thermocline contacts the substrate, appears to be a physical habitat feature for lake whitefish in some lakes. Lake whitefish also exhibited diurnal activity behaviour that was reflected through greater detection rates in the morning versus the afternoon. By accounting for imperfect detection, true estimated overall occupancy of lake trout and lake whitefish increased 0.15–0.30 over naïve occupancy. Thermal habitat envelopes for lake trout and lake whitefish are wider than previously thought. Lake trout occupied a consistent thermal habitat envelope while lake whitefish varied between lakes likely because of lake specific differences in basin morphology and wash zone.

Deciphering lifelong thermal niche using otolith δ18O thermometry within supplemented lake trout (Salvelinus namaycush) populations

“…Estimated temperatures, for all life stages, were consistent with published boundaries for this species’ thermal habitat, providing high confidence in the accuracy of this technique. Our results support the recent and growing realisation of a wider lake trout thermal niche than had been previously assumed (Challice, Milne, & Ridgway, 2019; Plumb & Blanchfield, 2009). Many authors emphasised the importance of among‐population variability in strategies for using available thermal resources in salmonids (Bergstedt et al, 2012; Elrod et al, 1996; McDermid et al, 2013).…”

Quantifying the Spatial Structure of Invasive Lake Trout in Yellowstone Lake to Improve Suppression Efficacy

“…Lake Trout in Yellowstone Lake were more aggregated during summer than other invasive Lake Trout populations (Dux et al 2011), probably in response to preferred environmental conditions or prey availability (Olson et al 1988;Blanchfield et al 2009;Plumb and Blanchfield 2009). Lake Trout require cold water temperatures (7.5-16.4°C; Challice et al 2019) with high dissolved oxygen concentrations (>6-7 mg/L; Evans 2007). Warm surface water temperatures and lake stratification in the summer force Lake Trout to seek refugia in the hypolimnion (Dux et al 2011;Guzzo et al 2017).…”

“…Warm surface water temperatures and lake stratification in the summer force Lake Trout to seek refugia in the hypolimnion (Dux et al 2011;Guzzo et al 2017). However, Lake Trout in some oligotrophic lakes exhibit thermally flexible habitat ranges extending past their maximum preferred temperatures (Challice et al 2019). Aggregations and movements of Lake Trout are also influenced by the distribution of prey species (Ahrenstorff et al 2011;Guzzo et al 2017).…”

Behavioural responses of a cold-water benthivore to loss of oxythermal habitat

“…Based on the thermal niche for lake whitefish defined by Christie and Regier (1988) of 10-14 °C, we used 10 °C as the upper threshold for optimal thermal habitat and 14 °C as the upper threshold for usable habitat. Recent research showing wild lake whitefish prefer primarily < 14 °C (Challice et al 2019) supports the use of these temperature thresholds. Optimal and usable DO thresholds for lake whitefish have not been as well defined as for other closely related coldwater species, such as lake trout.…”

“…As such, lake whitefish access to key invertebrate prey items is likely to become more physiologically challenging as their habitat becomes further constrained and they are forced to feed either within diminishing optimal oxythermal habitats or under suboptimal habitat conditions. Recent studies have highlighted variability in thermal habitat selection by lake whitefish among lakes (e.g., Gorsky et al 2012;Challice et al 2019), but because hypolimnetic DO was presumably not limiting in these studies (> 7 mg L −1 ; Challice et al 2019), habitat selection under both temperature and DO constraints is not known.…”