The effects of oxygen depletion due to upwelling groundwater on the posthatch fitness of Atlantic salmon (Salmo salar)

The conditions experienced by incubating Atlantic salmon (Salmo salar) eggs are strongly influenced by hyporheic exchange. In some rivers, periods of intense groundwater upwelling can reduce oxygen levels in the incubation zone to 0% saturation. The present study investigated the effect of oxygen sags on the posthatch fitness of Atlantic salmon. A laboratory experiment allowed fine-scale control of oxygen concentrations to replicate those induced by low oxygen groundwater in rivers. Extreme oxygen sags in the earlier stages of embryo development resulted in a developmental lag with alevin hatching later and at an underdeveloped state. At the latest stages of development, oxygen sags caused premature hatching of severely underdeveloped alevin. These findings combined with a review of the literature suggest posthatch survival of embryos exposed to groundwater-induced hypoxia will be lower because of predation and poor competitiveness.