Stream Habitats and Behavioral Interactions of Underyearling and Yearling Atlantic Salmon (Salmo salar)

Abstract

From an examination of over 20 yr of data from the Northwest Miramichi River and some additional data from small tributaries to the Nashwaak River, highest densities of 100 underyearling and 80 yearling or older Atlantic salmon (Salmo salar) per 100 m2 were found at sites where water velocities averaged 50–65 cm/s. At sites with lower or higher water velocities maximum observed densities decreased. Experiments in laboratory streams demonstrated that underyearling Atlantic salmon < 7 cm (total length) occurred in shallow (10–15 cm) pebbly (1.6–6.4 cm diam) riffles of natural streams by choice. As they grew they began to prefer deeper (> 30 cm) riffles with boulders (> 25.6 cm diam). Yearlings > 10 cm reduced the numbers of underyearlings < 6 cm in these deeper habitats by chasing them, and occasionally by catching and eating them. Social interactions, such as displays used in territorial defence, did not occur between yearlings and underyearlings until the latter exceeded 6.5 cm, the size at which they began to move to deeper riffles. Planting densities for hatchery-reared salmon recommended in the literature were refined, taking the space and habitat requirements of different-sized juvenile salmon into account. Key words: spatial relations, rearing capacity, stocking density, stream ecology

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

“…Intraspecific size or year-class compétition may influence survival and growth (see GIBSON, 1993), and habitat sélection in salmon parr (SYMONS and HELAND, 1978). Effects may vary, depending on population densities (HEGGENES and BORGSTR0M, 1991).…”

“…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).…”

Influence de fortes variations de niveau en étiage sur les mouvements et la distribution de saumons Atlantiques juvéniles (Salmo salar L.) en fonction de l'habitat dans un ruisseau expérimental

“…In summer, salmon parr prêter shallow water habitat, with depths between 10 and 50 cm (KEENLEYSIDE, 1962 ;SYMONS & HELAND, 1978 ;MORANTZ et al, 1987) and moderate current velocities of 5-15 cm.s ^ (MORANTZ et al, 1987 ;HUNTINGFORD et al, 1988). Thus, initial conditions in ail experiments were nearly optimal except water velocities in pools.…”

Étude expérimentale de la compétition interspécifique entre juvéniles de saumon coho, Oncorhynchus kisutch, et de saumon atlantique, Salmo salar, en eau douce

“…En présence des cohos, les jeunes saumons atlantiques sont cantonnés dans les radiers. Avec l'âge et la croissance en taille, ils préfèrent les radiers plus profonds ou l'entrée des profonds occupés par les juvéniles de coho (SYMONS et HELAND, 1978).…”