State–dependent shifts between nocturnal and diurnal activity in salmon

Abstract

Animal species have usually evolved to be active at a speci¢c time of the daily cycle, and so are either diurnal, nocturnal or crepuscular. However, we show here that the daily timing of activity in juvenile Atlantic salmon is related to the life-history strategy that they have adopted (i.e. the age at which they will migrate to the sea) and their current state (body size/relative nutritional state). Salmon can detect food more easily by day than by night, but the risk of predation is greater. Nocturnal foraging should generally be preferred, but the greater the need for growth, the greater should be the shift towards diurnal activity. In line with this prediction, all ¢sh were predominantly nocturnal, but salmon preparing to migrate to the sea, which would experience size-dependent mortality during the forthcoming migration, were more diurnal than ¢sh of the same age and size that were delaying migration for a further year. Moreover, the proportion of activity by day was negatively correlated with body size within the intending migrants. It has previously been shown that overwinter survival in ¢sh delaying migration is maximized not by growth but by minimizing exposure to predators. As predicted, daytime activity in these ¢sh was correlated with the prior rate of weight loss, ¢sh being more diurnal when their risk of starvation was greater. To our knowledge, these are the ¢rst quantitative demonstrations of state-dependent variation in the timing of daily activity.

Presence of larger flatfish modifies habitat preference by Age-0 northern rock sole Lepidopsetta polyxystra

“…The anti-predator tactics employed by rock sole and halibut (Lemke & Ryer 2006a) preclude foraging, and recent laboratory study demonstrated reduced growth in Age-0 rock sole exposed to chronic predation risk (C. H. Ryer & T. P. Hurst unpubl.). To mitigate chronic risk, fish may alter how and when they feed in a given habitat so as to minimize the ratio of predation risk to foraging reward (Fraser & Metcalfe 1997, Metcalfe et al 1998, Metcalfe & Steele 2001. Rock sole exhibit crepuscular activity peaks (Hurst & Duffy 2005), concentrating their feeding activity at dusk .…”

Partitioning of Time as an Ecological Resource

“…Salmon preparing to migrate to the sea, which would experience size-dependent mortality during migration, were more diurnal than fish of the same age and size that were delaying migration for a year (Metcalfe et al 1998). Dominant brown trout (Salmo trutta) preferred to forage during hours that are thought to minimize the predation risk incurred per unit of food obtained (Metcalfe et al 1999).…”

Effects of feed restriction on the upper temperature tolerance and heat shock response in juvenile green and white sturgeon

“…Maintenance of good nutritional status is critical because foodlimited fish are more susceptible to predation (Metcalfe et al, 1998;Steele, 2001), disease (Oliva-Teles, 2012), and other environmental factors (e.g., salinity; Haller et al, 2015;Lee et al, 2015). Energy allocation to different molecular and cellular pathways essential to the stress response can be limited in fish with reduced nutritional status (i.e., physiological trade-offs), resulting in decreased stress tolerance (Sokolova, 2013).…”