Oxygen uptake in Pacific salmon Oncorhynchus spp.: when ecology and physiology meet

Abstract

Over the past several decades, a substantial amount of research has examined how cardiorespiratory physiology supports the diverse activities performed throughout the life cycle of Pacific salmon, genus Oncorhynchus. Pioneering experiments emphasized the importance of aerobic scope in setting the functional thermal tolerance for activity in fishes. Variation in routine metabolism can have important performance and fitness consequences as it is related to dominance, aggression, boldness, territoriality, growth rate, postprandial oxygen consumption, life history, season, time of day, availability of shelter and social interactions. Wild fishes must perform many activities simultaneously (e.g. swim, obtain prey, avoid predators, compete, digest and reproduce) and oxygen delivery is allocated among competing organ systems according to the capacity of the heart to deliver blood. For example, salmonids that are simultaneously swimming and digesting trade-off maximum swimming performance in order to support the oxygen demands of digestion. As adult Pacific salmonids cease feeding in the ocean prior to their home migration, endogenous energy reserves and cardiac capacity are primarily partitioned among the demands for swimming upriver, sexual maturation and spawning behaviours. Furthermore, the upriver spawning migration is under strong selection pressure, given that Pacific salmonids are semelparous (single opportunity to spawn). Consequently, these fishes optimize energy expenditures in a number of ways: strong homing, precise migration timing, choosing forward-assist current paths and exploiting the boundary layer to avoid the strong currents in the middle of the river, using energetically efficient swimming speeds, and recovering rapidly from anaerobic swimming. Upon arrival at the spawning ground, remaining energy can be strategically allocated to the various spawning behaviours. Strong fidelity to natal streams has resulted in reproductively isolated populations that appear to be locally adapted physiologically to their specific environmental conditions. Populations with more challenging migrations have enhanced cardiorespiratory performance. Pacific salmonids are able to maintain aerobic scope across the broad range of temperatures encountered historically during their migration; however, climate change-induced river warming has created lethal conditions for many populations, raising conservation concerns. Despite considerable research examining cardiorespiratory physiology in Pacific salmonids over the last 70 years, critical knowledge gaps are identified.

Physiological condition and migratory experience affect fitness‐related outcomes in adult female sockeye salmon

“…Behavioural thermoregulation may be particularly important for females, which allocate considerable energy to gamete development in the final stages of maturation (Rand & Hinch, ); there is evidence that more mature females with lower levels of somatic energy occupy the coolest temperatures in natal lakes (Roscoe, Hinch, Cooke, & Patterson, ). Water temperature affects maturation rate (Pankhurst & King, ), and it has been proposed that occupying temperatures near T optAS allows migrating females to mature most efficiently (Eliason & Farrell, ); however, this has not been examined to date.…”

“…Water temperature affects maturation rate (Pankhurst & King, 2010), and it has been proposed that occupying temperatures near T optAS allows migrating females to mature most efficiently (Eliason & Farrell, 2016); however, this has not been examined to date.…”

The effect of thermal acclimation on aerobic scope and critical swimming speed in Atlantic salmonSalmo salar

“…Absolute AS is arguably more ecologically relevant because it provides a specific value for the aerobic capacity, and various aerobic tasks will have a specific oxygen cost, while it also makes for a better comparison between species and different life stages that may be very different in their energetics despite having similar factorial scopes (Clark et al, 2013;Eliason and Farrell, 2016). The absolute AS has therefore been the focus of this study.…”

“…Consequently, the scope for activity exhibits a thermal optimum (Fry and Hart, 1948;Brett, 1971;Eliason and Farrell, 2016). The temperature at which AS is maximized is associated with optimum growth (Brett, 1971;Claireaux et al, 2000;Mallekh and Lagardere, 2002;Khan et al, 2014) and the highest critical swimming speed (U crit ) in incremental swim speed protocols, which also coincides with maximum cardiac function (Brett, 1965;Farrell, 2002).…”

Bioenergetic consequences of warming rivers to adult Atlantic salmon Salmo salar during their spawning migration

“…The precise costs of swimming activity are presently not known because there are no long‐term studies of migrating Atlantic salmon energetics; therefore, we generated our model at several speeds. Speed is known to be closely linked to the life history of fishes (Eliason & Farrell, ; Glebe & Leggett, ). Bernatchez and Dodson () calculated the average swimming speed of Atlantic salmon (rivermouth to spawning grounds) to be 0.1 bl s −1 (using data from Belding, ), which is consistent with observations from telemetry that Atlantic salmon hold for long periods in slow‐moving pools prior to spawning (Lennox, Cooke, et al., ; Økland et al., ; Richard et al., ).…”