Publication Abstract

Effects of freshwater contaminants on marine survival in Atlantic salmon

W.L. Fairchild, S.B. Brown and A. Moore

There is increasing concern over the continuing decline of wild stocks of Atlantic salmon, Salmo salar, throughout the North Atlantic and the impact on commercial and recreational fisheries. Recent research has demonstrated that freshwater and marine environments cannot be considered in isolation and that conditions within the freshwater zone experienced by Atlantic salmon may be critical to their subsequent survival within the sea. In particular, exposure of juvenile salmon to a range of sub-lethal concentrations of freshwater contaminants such as pesticides and endocrine disrupting chemicals (EDCs) may operate to reduce survival in fish once they have emigrated to sea. Freshwater contaminants may act in a number of ways to reduce marine survival. Firstly, pesticides such as atrazine may interfere with the parr-smolt transformation (PST) and reduce the ability of the fish to physiologically adapt to saline conditions. Laboratory studies have indicated that smolts exposed in freshwater to environmental levels of the pesticide atrazine have lower gill Na⁺K⁺ATPase activity and plasma ion concentrations. Subsequent exposure to sea water resulted in poor hypoosmoregulatory performance and mortality. Moreover, modification of the physiological processes involved during smoltification by atrazine may also delay or inhibit smolt migration. Secondly, extensive studies have demonstrated a significant relationship between historical applications of an insecticide containing 4-nonylphenol (4-NP), a known EDC, and catch data for Atlantic salmon populations. This study suggested declines in catch were related to exposure during PST. Juvenile salmon were exposed to water-borne 4-NP (5 µg/L) or estrogen (100 ng/L) during the later stages of PST and their subsequent growth and survival followed for 5 months. Caged salmon smolts were also exposed in natural estuarinewaters and seawater growth and survival monitored for 3 months. Relative to reference groups, there was a greater proportion of salmon exhibiting poor sea water growth in exposed groups from both laboratory and field experiments. The response in all cases was bimodal, with growth effects occurring soon after treatments. Poor growth during the first months in the marine environment has been linked to reduced survival and fewer returns of adult salmon to their native streams. If the effects exerted by 4-NP are due to its estrogenic potential, then steroidogenic activity stemming from other sources (e.g. domestic sewage, agricultural, industrial) might influence salmon populations. Further work is continuing to determine the role of exposure to mixtures of contaminants on marine survival of salmon and to model impacts of contaminants on salmon populations.

Reference:

W.L. Fairchild*, S.B. Brown* and A. Moore* (2002) Effects of freshwater contaminants on marine survival in Atlantic salmon. North Pacific Anadromous Fish Commission, Technical Report 4,  30-32.