Synergistic effect on mortality in Atlantic salmon, Salmo salar, smolt caused by osmotic stress and presence of predators

Abstract

SynopsisThe hypothesis that an increase in the mortality rate of Atlantic salmon would be produced by the synergistic effect of osmotic stress and of stress due to the presence of predators was tested by putting two groups of smolts (one acclimated to seawater and the other not acclimated) into a tank containing predators. These smolts were tested afterwards in a seawater-challenge test, together with smolts of the control groups for both experimental groups. The mortality rate of the non-acclimated and predator-exposed smolts was 90%) and that of the seawater acclimated and predator-exposed smolts 43%) compared to no mortality among the control groups. Lack of acclimation to seawater did not in itself induce any lethal stress, but in conjunction with predator-stress there was a synergistic effect, leading to an increase in the mortality rate. The hypothesis is therefore considered to be valid.

Correlates of estuarine survival of Atlantic salmon postsmolts from the Southern Upland, Nova Scotia, Canada

“…Predators have been reported to favour the area around head-of-tide or at constriction points within estuaries during the smolt run (Hvidsten and Lund 1988;Dieperink et al 2002;Jepsen et al 2006). Salmon are first exposed to salt water in the inner estuary and mortality may occur as a result of osmotic stress or an associated reduction in predator avoidance ability (Järvi 1989;Handeland et al 1996). Body size, particularly the disproportionate increase of volume to surface area, may be an important determinate of a smolts ability to deal with osmotic stress (Parry 1960;Muir 1969).…”

“…Using acoustic telemetry, researchers have estimated mortality rates during the estuarine migration, which is the transition point from riverine to marine habitats, the place the fish spend their first few weeks in the ocean, and a place and time where previous studies have reported intense mortality (Kocik et al 2009;Davidsen et al 2009;Halfyard et al 2012). Causes of estuarine losses may include predation (e.g., Hvidsten and Møkkelgjerd 1987;Hvidsten and Lund 1988;Dieperink et al 2002), osmotic stress (Staurnes et al 1996;McCormick et al 1998), and (or) their interaction (Järvi 1989;Handeland et al 1996).…”

A comparison of single and multiple stressor protocols to assess acute stress in a coastal shark species, Rhizoprionodon terraenovae

“…This complicates the execution of physiological studies on fishes because stress protocols typically require removal of the animal from the water to effectively obtain samples, thereby eliciting additional stress. Past studies on fishes have shown that increasing the number of additional stressors can have a cumulative or synergistic effect, increasing stress response variables such as circulating lactate and cortisol levels (Järvi 1989;Pankhurst and Van Der Kraak 1997;Davis 2002;Campbell et al 2010). Among cartilaginous fishes, recent studies have focused on achieving a greater understanding of the generalized elasmobranch response to capture stress; however, methodologies varied among studies depending on the gear used to capture the sharks and the duration of the stress event (e.g., Hoffmayer and Parsons 2001;Manire et al 2001;Frick et al 2009;Mandelman and Skomal 2009), rendering comparative evaluation difficult.…”

Seaward migrating Atlantic salmon smolts with low levels of gill Na+, K+ -ATPase activity; is sea entry delayed?

“…Several studies have shown that post-smolts are exposed to high predation immediately after sea entry (Reitan et al 1987;Hvidsten and Lund 1988;Dieperink et al 2002) and that the risk of predation increases if fish suffers from osmotic stress (Järvi 1989;Handeland et al 1996;Kennedy et al 2007). It may therefore be suggested that the extended residency of the first smolt group in the lower part of the river was related to their low gill Na + , K + -ATPase activity and a need to improve seawater tolerance before entering seawater.…”