In situ and laboratory studies on the behaviour and survival of Pacific salmon (genus Oncorhynchus)

Abstract

Experiments in an estuary receiving a surface discharge of treated pulp mill wastes revealed conditions which were lethal to underyearling salmon at, and below the halocline (4.0-6.5m depth). Juvenile chinook salmon were biased towards the water surface and avoided waters at depth. Dissolved oxygen was the variable which affected this distribution most significantly. Surface waters receiving effluent from another pulp mill were lethal to juvenile salmon within 350m, and a significant vertical avoidance response occurred within 350-950m of the outfalls. The behavioural response was signficantly correlated with temperature, pH and colour (effluent). Experimental induction of hypoxic conditions in fresh water elicited a downward distribution shift towards the halocline and oxygenated, but more saline, waters. Avoidance reactions (50% level) occurred consistently up to 7-8mg.l-1 dissolved oxygen. Salmon continued to examine the hypoxic freshwater zone despite sub-optimal conditions. -from Authors