Seasonal Variations in the Smolt Characteristics of Juvenile Atlantic Salmon (Salmo salar) from Estuarine and Riverine Environments

Abstract

Smolt characteristics such as lipid-moisture dynamics, ATPase activity, salinity tolerance, and condition factor were determined for Atlantic salmon parr (Salmo salar) moving to, or residing in, estuaries of two rivers in eastern Canada. Lipid and water content and gill Na+K+-ATPase activity of these parr differed markedly from river-resident parr. ATPase activity, sex ratio, and condition factor indicated more similarity between estuarine parr and smolts. Estuarine parr were unable to tolerate high salinities in spring, summer, or autumn, but there was an indication of an autumnal increase in salinity tolerance which coincided with maximum levels in ATPase activity and a secondary downstream movement of parr and smolt-like salmon in the autumn. The data suggest that the largest estuarine parr are essentially presmolts which utilize the estuary as a rearing environment prior to subsequent emigration seaward when environmental conditions are again amenable to a reopening of the 'smolt window.' These observations also highlight some inadequacies in applying existing criteria for the smoking process and for modelling life histories of salmonids.

Seasonal Variation in Estuarine Habitat Use by Native Atlantic Salmon (Salmo salar) and Invasive Brown Trout (Salmo trutta) in Southeast Newfoundland

“…However, we found that small parr-sized Atlantic Salmon used the Renews River estuary extensively, especially in spring. This finding is consistent with observations from a few other studies (Cunjak 1992;Cunjak et al 1989Cunjak et al , 1990Thorpe 1994), and suggests juvenile Atlantic Salmon exploit estuaries to a greater extent in eastern Canada than Europe. Differences in habitat use by Atlantic Salmon in Europe and North America may be due to the presence or absence of Brown Trout.…”

“…The extensive work on estuarine use by Atlantic Salmon parr conducted by Cunjak (1992) and colleagues (Cunjak et al 1989(Cunjak et al , 1990 in northern Newfoundland was in an area not yet colonized by Brown Trout. Here we provide the first comparison of estuary use between Brown Trout and Atlantic Salmon in a North American watershed, by season, for different size classes.…”

Atlantic salmonSalmo salarL., brown troutSalmo truttaL. and Arctic charrSalvelinus alpinus(L.): a review of aspects of their life histories

“…In addition, estuaries are often used by Atlantic salmon parr for rearing prior to smolting (Cunjak et al. 1989; 1990; Cunjak 1992). Cunjak (1992) reported that growth of estuarine parr was highly variable but was faster than in riverine habitat and could be due, in part, to greater feeding opportunities in estuarine areas.…”

The Physiological Basis of the Migration Continuum in Brown Trout (Salmo trutta)

“…This transformation is characterized by an increase in gill Na,K-ATPase activity and a decrease in condition factor; both measures are widely used indicators of the smoltification process and anadromy (McCormick et al 1985;Cunjak et al 1990;McCormick and Bjornsson 1994;Reis-Henriques et al 1996;Sigholt et al 1998;Aarestrup et al 2000). In most studies of smoking anadromous salmonids, giU Na,K-ATPase activity correlates positively with improved seawater tolerance, and increased gill Na,K-ATPase activity has thus been interpreted as a preparatory biochemical change in anticipation of the transition to the marine environment.…”