Comparative thermal biology and depth distribution of largemouth bass (Micropterus salmoides) and northern pike (Esox lucius) in an urban harbour of the Laurentian Great Lakes

Understanding how individuals are distributed in space and time, as well as how they interact with dynamic environmental conditions, represent fundamental knowledge gaps for many fish species. Using acoustic telemetry tags, we monitored the temperatures and depths used by northern pike (Esox lucius L., 1758) and largemouth bass (Micropterus salmoides (Lacepède, 1802)) in Toronto Harbour (Lake Ontario). Northern pike and largemouth bass had similar thermal experiences throughout the year, except during summer, when northern pike were observed in cooler waters than largemouth bass. Both species used different depths throughout the year, with northern pike occupying deeper depths. Statistical modelling indicated that depth usage was influenced by all variables (season, species, and body size) and interactions between them, whereas thermal preferences were influenced by the main effects and interactions between species:season and species : body size. Both species were observed at temperatures warmer than those in the vicinity of nearby telemetry stations, but as station temperatures exceeded 20 °C, northern pike moved into cooler water, indicating active thermoregulation. These data will be useful for refining our understanding of the spatial ecology of fish and for informing fisheries and habitat management in this and other urban harbours of the Laurentian Great Lakes.