Realized thermal niche and habitat use are two conceptualizations of fish habitat based on organismal performance or lake-specific ecology, respectively. Both habitat types were compared for lake trout (Salvelinus namaycush) and brook trout (S. fontinalis) co-occurring in four large (> 500 ha) oligotrophic lakes. Lakes were partitioned into two morphological categories based on possession of a central or non-central deep basin with corresponding differences in adjoining shelf areas. Lake asymmetry in basin location has been shown to strongly influence food web connections based on isolation of basins from shelf areas.

Generally, overlap between both habitat types occurred in several comparisons with lake trout, suggesting that thermal habitat is a reasonable proxy for habitat use boundaries though not a full replacement for insights gained from habitat use models.

For brook trout, overlap was not as consistent, especially for lakes with non-central basins. In central basin lakes, there were closer proximity between the two species and overlap in both thermal niche and habitat use models. There was very limited overlap of either habitat type in lakes with non-central basins. Further, there were no shared areas of interspecific overlap between thermal niche and habitat use in non-central basins pointing to additional complexity governing habitat partitioning between lake trout and brook trout in these types of lakes. The shelf area effect on spatial structure of habitat, and likely food web connections, can occur in lakes regardless of basin centrality so long as shelf areas are large. In this lake set, lakes were sufficiently large to observe this phenomenon.

Data are from one-hour set duration benthic gill-netting depth stratified randomized netting surveys conducted in four large lakes in Algonquin Provincial Park using standard North American large-mesh gillnets. Surveys were conducted during periods of thermal stratification (July-August) in the daytime. Each site was sampled at least three times during a survey. 

Lake volumes for hypsographic data were derived from digital bathymetric surveys conducted by Harkness Lab staff. ArcGIS software was used to calculate lake volume at 1 metre resolution from the digital bathymetry rasters. Temperature and DO profiles were collected mid-basin in each lake during the netting surveys. 

Data and code to replicate the occupancy and overlap analysis and figures are provided in .Rdata files and can be opened in the R Statistical computing language. Analysis code is provided as .R scripts and is commented.  .R files can be opened in any R editor, but are best viewed in RStudio. .Rdata files can be opened in any instance of R. Files are provided in a compressed file containing all files to replicate the analysis found in the paper.

To recreate the hypsographic figure lake volume data is provided in a .csv file and lake outlines and contours in a .gpkg file. Both of these can be opened in code provided in a .R file which can be used in R or RStudio.