Linking Behavior, Physiology, and Survival of Atlantic Salmon Smolts During Estuary Migration

Abstract

Decreased marine survival is identified as a component driver of continued declines of Atlantic Salmon Salmo salar. However, estimates of marine mortality often incorporate loss incurred during estuary migration that may be mechanistically distinct from factors affecting marine mortality. We examined movements and survival of 941 smolts (141 wild and 800 hatchery‐reared fish) released in freshwater during passage through the Penobscot River estuary, Maine, from 2005 to 2013. We related trends in estuary arrival date, movement rate, and survival to fish characteristics, migratory history, and environmental conditions in the estuary. Fish that experienced the warmest thermal history arrived in the estuary 8 d earlier than those experiencing the coolest thermal history during development. Estuary arrival date was 10 d later for fish experiencing high flow than for fish experiencing low flow. Fish released furthest upstream arrived in the estuary 3 d later than those stocked further downstream but moved 0.5 km/h faster through the estuary. Temporally, movement rate and survival in the estuary both peaked in mid‐May. Spatially, movement rate and survival both decreased from freshwater to the ocean. Wild smolts arrived in the estuary later than hatchery fish, but we observed no change in movement rate or survival attributable to rearing history. Fish with the highest gill Na+, K+‐ATPase activity incurred 25% lower mortality through the estuary than fish with the lowest gill Na+, K+‐ATPase activity. Smolt survival decreased (by up to 40%) with the increasing number of dams passed (ranging from two to nine) during freshwater migration. These results underscore the importance of physiological preparedness on performance and the delayed, indirect effects of dams on survival of Atlantic Salmon smolts during estuary migration, ultimately affecting marine survival estimates. Received October 25, 2014; accepted January 8, 2015

Shorter juvenile telomere length is associated with higher survival to spawning in migratory Atlantic salmon

“…Smolt “physiological preparedness” can be quantified by measuring the abundance of Na + ‐K + 2Cl − cotransporter (a protein associated with ion regulation) and/or the activity of the associated Na + ‐K + 2Cl − ATPase enzyme, both of which are up‐regulated in Atlantic salmon smolts prior to sea entry (Pelis & McCormick, ; Stich, Zydlewski, & Zydlewski, ). Moreover, it has been found that individuals investing more in physiological preparedness immediately prior to migration (in terms of higher K + 2Cl − ATPase activity) subsequently experience reduced mortality (Stich, Zydlewski, Kocik, & Zydlewski, ). However, these physiological changes are also associated with changes in circulating hormone levels during smolting.…”

Physiological preparedness and performance of Atlantic salmon Salmo salar smolts in relation to behavioural salinity preferences and thresholds

“…Conversely, transit time from rkm 30 to the mouth of the estuary was not related to gill NKA activity. Previous research has failed to detect differences in estuarine movement rates based on gill NKA activity in the Penobscot Estuary (Stich et al , ), but that study did not attempt to separate movement rates based on location of SW in the estuary. It appears that S .…”

“…Recently, survival of S . salar smolts during estuary migration has also been related to activity of gill NKA activity immediately prior to migration (Stich et al , ), highlighting the importance of physiological development for successful SW entry.…”

Release during night enhances survival of wild Atlantic salmon smolts

“…However, no single factor has yet been identified that can fully explain the lack of returns. Considerable scientific attention has been paid to the effects of release strategy and the quality of hatchery smolt upon release (Stich, Zydlewski, Kocik & Zydlewski, ; Vainikka et al., ). Several studies have demonstrated that hatchery smolts behave differently (Aarestrup, Baktoft, Koed, del Villar‐Guerra & Thorstad, ; Jonsson, Jonsson & Hansen, ; Thorstad, Uglem, et al., , Thorstad, Whoriskey, et al., ) and have lower survival rates than wild conspecifics (Jonsson et al., ; Thorstad et al., ).…”