Development of a short-term in situ caging methodology to assess long-term effects of industrial and municipal discharges on salmon smolts

Trial experiments to develop an in situ method for determining effects of short-term exposure to contaminants on salmon during the sensitive smolt stage were carried out. Wild Atlantic salmon (Salmo salar) smolts were caged at various estuarine locations in northeast New Brunswick, Canada at different levels of anthropogenic impact in 2000 and 2001. Survival, growth (weight and K), and feeding (delta C-13 and delta N-15) parameters were measured following summer grow-out at a hatchery. A summary of distributions of the four parameters indicated that smolts caged at locations receiving lower levels of industrial and municipal discharges feed and grow better than those caged at sites receiving higher levels. The findings, however, were not repeatable between the 2 years studied. The observed inconsistency between years may be a consequence of the relatively low concentrations of alkylphenolic contaminants (putative causative agents) and overall steroidogenic potency in river water at the time of caging. Differences in temperature and salinity from 2000 to 2001 may have further confounded comparisons across treatments and between years. In future studies, caging in closer proximity to industrial and municipal discharges or in systems with higher concentrations of waterborne contaminants or impoundments would help further the assessment and applicability of this methodology and allow a more robust comparison of smolt feeding and growth among reference and exposure sites. (c) 2005 Elsevier Inc. All rights reserved.