VANN. Impact of environmental contaminants on smolt physiology, migration and marine survival in wild Atlantic salmon.

Pre-smolts will be exposed to environmentally relevant levels of contaminants known to occur in those Norwegian rivers supporting spawning populations of wild Atlantic salmon. The proposal will focus primarily on agricultural contaminants (pesticides), al though putative endocrine disrupters and acid/Al, which wild salmon are exposed to episodically, will also be investigated. As the olfactory nervous system in salmon (important in migration and homing) is sensitive to a wide range of anthropogenic contami nants, test compounds (especially pesticides) will be screened for their ability to disrupt olfactory sensitivity using electrophysiological techniques (EOG response). Following exposure during the sensitive period of parr-smolt transformation, smolt phys iology will be evaluated from well established parameters including gill Na+K+ATPase levels and plasma hormone profiles. In addition, hypo-osmoregulatory ability will be evaluated using seawater challenge tests. In order to correlate whether disruption in smolt physiology and/or olfactory function due to contaminant exposure can be correlated to impaired downstream migration, groups of tagged, previously exposed fish will be released into a river system after the completion of smoltification. Downstream m igration will be evaluated from capture rates in fish traps downstream. In combining physiological, behavioural and ecological studies, the proposal will determine whether there is a causal link between exposure to anthropogenic factors during the early f reshwater life-history stages and subsequent smoltification, and downstream migration. These results will be of value to existing salmon life-history models in order to predict the impact of water quality on stocks and populations of wild Atlantic salmon.