Field Observations of Deformed Atlantic Salmon (Salmo salar) Embryos Incubated in the Hyporheic Zones of Seven Cold Region Rivers

There is little research reporting deformities of naturally incubating salmonid embryos. The objective of this study was to report the prevalence of deformed Atlantic salmon (Salmo salar) embryos across a range of incubation habitats. We assessed 3234 embryos that had been incubated to approximately the “eyed” stage in simulated redds at 20 sites in seven rivers across two basins (the Tobique and the Miramichi River basins of northern New Brunswick, Canada) over three winters (2012–2015). A range of incubation habitats were represented: regulated rivers warmed by bottom-draw dams; unregulated, ice-covered rivers of different sizes; and a long-residence groundwater-fed brook that remained ice free. Deformities were unusually prevalent (1.4–95.7% deformed) in the Tobique River basin compared with the Miramichi River basin (0–7.7%) and hatchery controls (1.1%). Within the Tobique River basin, warmer sites near dams had the fewest deformities. Deformity data were collected opportunistically as part of other studies within our research group, therefore, we do not make any firm conclusions about what environmental or intrinsic factors may have contributed to the prevalences reported herein; instead, we discuss pertinent differences between basins and present possible hypotheses for future study.