Spatiotemporal ecology of juvenile Muskellunge (Esox masquinongy) and Northern Pike (Esox lucius) in upper St. Lawrence River nursery bays during their inaugural fall and winter

Abstract Understanding the spatial ecology of juvenile freshwater fish beyond summer months is an essential component of their life history puzzle. To this end, declines in the natural populations of sympatric Muskellunge ( Esox masquinongy ) and Northern Pike ( Esox lucius ) in the upper St. Lawrence River prompted study of spatiotemporal patterns and habitat requirements associated with earlier life stages of these congeneric, freshwater predators in fall and overwinter periods. Over 75 age‐0 esocids were tagged and passively monitored using acoustic telemetry in four nursery embayments in fall and winter months from 2015 and 2017 months to elucidate spatiotemporal ecology and test hypotheses related to emigration. Presence, residency, space and habitat use were assessed and modelled against key environmental (i.e. water temperature and level) and biological (total length) covariates using mixed effect models. Muskellunge were found to spend more time in deeper, littoral regions with canopy‐forming, submerged aquatic vegetation while Northern Pike aggregated in the deepest, highly vegetated region of their nursery embayment. Results suggest fish may exhibit transitionary movements in fall months and may span outwards into nearshore regions along the main river channel. Studies informing coastal restoration initiatives to increase Muskellunge production are encouraged to assess sympatric habitat use relative to prominent embayment structures and further explore depth partitioning by these young predators. With a substantial influence from water‐level regulation on use of nursery habitat, future studies must work in concert with management plans aimed at producing more natural riverine cycles and thus increased recruitment of Esox species.