Feeding behaviour of wild Atlantic salmon, Salmo salar L., parr in mid- to late summer in a Scottish river

Abstract

From 25 July to II September 1984 Atlantic salmon, Salmo salar L-, parr were observed underwater between 0800 and 1600 h, feeding actively from defended territories at two sites in the River Tilt, Perthshire, Scotland. Territories comprised one or more preferred stations on or just above the substrate, from which the fish intercepted drifting particles (75% of feeding), or foraged on the substrate (25%). Drift feeding occurred 36% at the surface. 35% in mid-water and the remainder at the feeding station. 35% of prey particles were attacked directly from the feeding station, and 65% indirectly after preliminary inspection, sometimes involving a drift downstream by the fish. 20% of captures were made upstream of the station and 80% downstream. 12-15-cm fish fed more frequently at the surface, while lO-cm fish fed in mid-water or at their stations. Surface feeding decreased proportionately during rainfall. Frequency of feeding increased with temperature. Feeding was depressed in the presence of large saimo nids.

Note de synthèse sur la sélection de niche spatiale et la compétition chez le jeune saumon Atlantique (Salmo salar) et la truite commune (Salmo trutta) en milieu lotique

“…Social interactions are évident. Dominant parr may be aggressive (SYMONS and HELAND, 1978) and the présence of large salmon or trout can depress feeding in salmon parr (STRADMAYER and THORPE, 1987 ;HUNTINGFORD et al, 1993). Such interactions may influence microposition choice by subordinate parr (KEENLEYSIDE and YAMAMOTO, 1962 ;GIBSON, 1988).…”

The costs of becoming nocturnal: feeding efficiency in relation to light intensity in juvenile Atlantic Salmon

“…To test the ability of the fish to detect and intercept food items moving in the water column (since drifting invertebrate food forms the majority of their diet; Keenleyside 1962;Maitland 1965;Stradmeyer & Thorpe 1987), we adopted the technique of Jørgensen & Jobling (1990 and prevented the fish from taking stationary or slowly moving food on the floor of the tank by holding them in a 60 x 30 cm 2 net enclosure suspended 10 cm above the tank floor.…”

“…Stream-living species such as the Atlantic Salmon Salmo salar L. rely almost entirely on vision to detect their prey (which is mostly in the form of drifting invertebrates): the fish dart out from a vantage position to intercept items of drift being carried past in the current (Keenleyside 1962;Stradmeyer & Thorpe 1987). Do salmon maintain their ability to detect prey items when they switch from diurnal to nocturnal foraging?…”

Mobility and home-range use of Atlantic salmon parr over short time scales

“…In the future, combined studies using biotelemetry and visual observations while snorkeling could improve the knowledge on the relation between social status and mobility in Atlantic salmon parr as well as of motivations controlling movement and space use in Atlantic salmon parr. The classical view of the mosaic distribution of territories was not confirmed; instead parr had overlapping home ranges as it has been observed elsewhere (Stradmeyer and Thorpe 1987;Armstrong et al 1999;Martin-Smith and Armstrong 2002;Økland et al 2004).…”