Thermal niche and habitat use by co-occurring lake trout ( Salvelinus namaycush ) and brook trout ( S. fontinalis ) in stratified lakes

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 was 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 was 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.