Evidence for cumulative temperature as an initiating and terminating factor in downstream migratory behavior of Atlantic salmon (Salmo salar) smolts

Abstract

Temperature control of Atlantic salmon (Salmo salar) smolt migration was tested using a novel technique allowing nearly continuous monitoring of behavior with complete control over environmental conditions. Parr and presmolts were implanted with passive integrated transponder tags, placed in simulated streams, and monitored for upstream and downstream movements. Beginning 18 April, temperature was increased 1 °C every third day (advanced), fourth day (ambient), and tenth day (delayed). Smolt downstream movements were initially low, peaked in mid-May, and subsequently declined under all conditions. Parr downstream movements were significantly lower than those of smolts in all treatments (0.8 ± 0.5 movement·day–1 versus 26.5 ± 4.5 movements·day–1, mean ± SE) and showed no increase. At delayed temperatures, smolts sustained downstream movements through July; those under ambient and advanced conditions ceased activity by mid-June. Initiation and termination of downstream movements occurred at significantly different temperatures but at the same number of degree-days in all treatments. Physiological changes associated with smolting (gill Na+,K+-ATPase activity and plasma thyroxine) were coincident with behavioral changes. This is the first evidence of a behavioral component to the smolt window. We found that temperature experience over time is more relevant to initiation and termination of downstream movement than a temperature threshold.

The role of temperature and flow on the migration of Chinook salmon (Oncorhynchus tshawytscha) smolts.

“…Models with ATU also consistently had lower AIC C scores than did the same model with temperature. This finding is in agreement with Zydlewski et al (2005), who found that in a controlled experiment, temperature experience was more relevant to both the initiation and termination of downstream movement of…”

“…Without the ability to control variables while manipulating others, it is difficult to assess their relative importance to the migration process. For example, Zydlewski et al (2005) experimentally manipulated temperature and found that cumulative temperature was more of a factor in initiating and terminating migration in Atlantic salmon than was a particular temperature threshold. However, other factors, such as increased flow, were not included in that study.…”

“…Following the procedure outlined by Zydlewski et al (2005) each of the experimental tanks had an oval barrier installed in the middle to force fish to travel around the outside of the tank (Figure 8). At the narrowest point, the distance between the barrier and the edge of movements.…”

“…The current experiment was based on that of Zydlewski et al (2005) and Fangstam et al (1993), and was expanded to investigate the role of flow velocity in addition to temperature and focuses on…”

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

“…The timing of the onset and completion of the smolting process is governed by photoperiod and water temperature, respectively (Solbakken et al 1994;Handeland et al 2003;Zydlewski et al 2005), while water temperature and water flow are key factors for the initiation of seaward migration (McCormick and Saunders 1987;McCormick et al 1998). A successful sea entry presupposes that the completion of the smolt development is synchronised with the timing of migration.…”