Swimming Behavior of Salmonid Fish in Ocean Pens

Abstract

Based on personal observations and questionnaires to Norwegian fish farmers, the behavior of three species and several different stocks of salmonid fish reared in ocean pens is described. Swimming activity and the constancy of swimming orientation (clockwise or counter clockwise) vary among species. With few exceptions, the orientation of Atlantic salmon (Salmo salar) at any one farm does not change with tide, season, or age offish. Stock origin and/or the early rearing history may impose this directionality. The swimming of Atlantic salmon in pens resembles schooling behavior. Possible departures from this stereotyped behavior are considered. The behavior of pen-reared salmonids and its implications in selective breeding, migratory mechanisms, and fish health are discussed. Key words: salmon, behavior, pen rearing, mariculture, swimming, orientation, Salmo salar, S. gairdneri, Oncorhynchus gorbuscha

Not too slow, not too fast: water currents affect group structure, aggression and welfare in post-smolt Atlantic salmon Salmo salar

“…In the marine life stages, wild salmonids swim on average at 1 body length (BL) s −1 (Drenner et al 2012). This is similar to observed swimming speeds in salmon farms (Sutterlin et al 1979, Kadri et al 1991, Blyth et al 1993, Juell & Westerberg 1993. In the wild, this cruising speed is suggested to be the energetic optimum with lowest cost of transport (Drenner et al 2012).…”

The behaviour of Atlantic salmon in relation to efficient cage-rearing

“…Schooling salmon swim continuously, but not at a constant speed. Swimming speeds that average from 0.2 to 1.9 body lengths per second (BL s -1) have been observed (Sutterlin et al, 1979;Kadri et al, 1991;Blyth et al, 1993;JueU and Westerberg, 1993;Smith et al, 1993). Swimming speed seems to increase towards the edge of the cage (Sutterlin et al, 1979;Fernti et al, 1988) and varies with season (Fern0 et al, 1988;Juell and Westerberg, 1993) and time of day.…”

“…GROUP BEHAVIOUR Direct observation through a pair of polarized glasses is a valuable and simple method of recording the main modes of behaviour in high-density groups of fish in sea cages. Using this method Sutterlin et al (1979) found that the swimming direction of Atlantic salmon may differ between cages at one farm, but usually does not change with tide, season or age in one particular cage. Stock-related swimming behaviour (Fern6 et al, 1988), hunger-dependent surface activity during feeding (Juell, 1988;Blyth et al, 1993) and stress-related leaping activity have also been recorded by this method.…”

“…Direct visual observation of fish with fluorescent tags has been used with some success to identify size groups (Sutterlin et al, 1979). Identification of individuals with pattern-coded tags is an interesting method, but it demands larger tags, good contrast and the correct angling of the tag to the observer.…”

“…Similar behaviour has been reported in caged rainbow trout, Oncorhynchus mykiss (Kils, 1989). The swimming direction (clockwise or counterclockwise) can differ from cage to cage at one farm (Sutterlin et al, 1979;Smith et al, 1993) and between subgroups within the same cage (Fern6 et al, 1988). Schooling salmon swim continuously, but not at a constant speed.…”