Temperature-dependent switch between diurnal and nocturnal foraging in salmon

Abstract

The activity patterns of animals, whether diurnal, crepuscular or nocturnal, are usually fixed endogenous rhythms, entrained by environmental Zeitgebers. Here we demonstrate that juvenile Atlantic salmon, Salmo salar, switch between diurnal and nocturnal foraging solely in response to environmental temperature, and independently of photoperiod and season. Above 10 °C juvenile Atlantic salmon fed predominantly during daylight, spending the night exposed in the water column but relatively quiescent. As temperature dropped below 10 °C they became increasingly nocturnal, hiding in refuges by day but emerging to feed at night. It has previously been shown that parallel physiological changes take place in the retinae of several species of salmonids : the quantity and composition of the visual pigments change so as to make the fish more dark adapted at low temperatures. As the fish were found to be far less aggressive by night than by day at all temperatures, the switch to nocturnal activity was also accompanied by a change in social structure. We suggest that this temperature-dependent strategy maximizes feeding efficiency in summer but reduces predation risk in winter.

A functional model for maximum growth of Atlantic Salmon parr, Salmo salar, from two populations in northwest England

“…The parr often fed at this low light intensity, especially at the lower temperatures (< 9·5°C). Similar observations on nocturnal feeding at low temperatures have been made by Fraser et al (1993).…”

“…Salmon parr in a Scottish stream and Nova Scotian river ceased growing, reduced their feeding activity and hid among stones in winter at temperatures below 6-7°C (Gardiner & Geddes 1980;Cunjak 1988), but other workers conclude that winter inactivity occurs below 9°C (Gibson 1978;Rimmer, Paim & Saunders 1983). However, these observations were made during the day and it is possible that there was a temperaturedependent switch from diurnal to nocturnal foraging as shown in the laboratory by Fraser, Metcalfe & Thorpe (1993). The lower threshold for growth in the field has been given as 7°C (Symons 1979;Evans, Rice & Chadwick 1985), 6°C (Power 1969), 5·6°C (Lee & Power 1976) and 6·3-7·4°C (Jensen & Johnsen 1986;Jensen, Johnsen & Saksgard 1989).…”

Different effects of temperature on foraging activity schedules in sympatric Myrmecia ants

“…The maintenance of such discrete seasonal and daily activity patterns allows animals to avoid predators, to reduce conflict with competitors and to optimally exploit food resources (Schoener, 1974;Kronfeld-Schor and Dayan, 2003). To determine suitable times of activity, animals may monitor environmental variables such as light (Kotler et al, 1991;Elangovan and Marimuthu, 2001;Narendra et al, 2010) and temperature (Grubb, 1978;Fraser et al, 1993) as well as anticipate daily events such as sunrise and sunset with the aid of their internal circadian clocks (de Groot, 1983;Welbergen, 2008).…”

Habitat Choice by Atlantic Salmon Parr in Relation to Turbulence at a Reach Scale

“…However, Orpwood et al (2006) showed, in contrast, that parr may be diurnal only to the extent needed to sustain their growth rate, which depends on food availability, supporting our results. During autumn and winter when water temperature drops below 8-128C, parr shelter in the interstitial space of the substrate during the day (Rimmer et al 1983;Cunjak 1988) and emerge at darkness to feed (Fraser et al 1993;Valdimarsson et al 1997). Consequently, Atlantic salmon parr are known to display complex diel activity patterns and cannot be considered as entirely diurnal, crepuscular, or nocturnal.…”