Food consumption and growth of Atlantic salmonSalmo salarparr in sub‐Arctic rivers: empirical support for food limitation and competition

Abstract

The quantitative food consumption and somatic growth of Atlantic salmon Salmo salar parr were compared between three sub-Arctic rivers in northern Norway and Finland, addressing the potential occurrence of resource limitation and interspecific competition. In one of the rivers, previous resource partitioning studies have suggested severe dietary competition between juvenile S. salar and a dense population of alpine bullheads Cottus poecilopus. It was hypothesized that S. salar parr in this river would have restricted food consumption and growth rates compared to the S. salar populations in the other two rivers where interspecific competition was less likely to occur. The feeding and growth performance differed significantly between the S. salar populations. The lowest food acquisition and growth rates were in the S. salar parr population living in sympatry with C. poecilopus, confirming a restricted food supply for the S. salar parr and providing empirical support for the presence of resource limitation and interspecific food competition in this river system. The study reveals that S. salar parr in sub-Arctic rivers may experience food limitations resulting in diminished growth rates.

Weekly changes in prey availability for and the selective feeding of sea trout (Salmo trutta L.) larvae stocked in small forest streams

“…The fork length, weight, and condition factor values are similar to the results reported for other stages and species of salmonids at the same age (Ró¿añska 1961, Amundsen and Gabler 2008, Domaga³a et al 2014, Czerniawski et al 2015. The lack of significant differences in the condition factor values between the streams and the high similarity in the growth of the fish from both streams means that both streams offer sufficient food and environmental 140 Józef Domaga³a et al conditions for the growth of fry at the given density.…”

“…Salmonid fry usually prefer larval Ephemeroptera, Plecoptera, and Diptera as their prey, while larval Coleoptera and Gammaridae are also relatively abundant among the prey items consumed (Strandmeyer and Thorpe 1987, Amundsen and Gabler 2008, Domaga³a et al 2014. The composition of the food base was usually reflected in the stomach contents of the fish studied, and the dominant taxa at a given site were also most abundantly represented in the stomach contents.…”

“…As we considered in our previous study (Domaga³a et al 2014), one of the ways stocking effectiveness of trout Salmo trutta L. larvae or fry can be improved is to ensure the availability of prey as food, mainly invertebrates, which are the main component of the diet of juvenile salmonids in the wild (Klemetsen et al 2003, Amundsen andGabler 2008). The main factor determining the availability of prey organisms as food is the size ratio between the predator and the prey (Wankowski andThorpe 1979, Strandmeyer andThorpe 1987).…”

Feeding strategies, resource utilisation and potential mechanisms for competitive coexistence of Atlantic salmon and alpine bullhead in a sub-Arctic river

“…We have furthermore documented diminished feeding and growth rates of the Atlantic salmon population in this system relative to salmon populations from comparable rivers where the alpine bullhead is not present, thus providing empirical support for the presence of resource limitation and interspecific food competition (Amundsen and Gabler 2008). Considering the extensive niche overlap and in light of the competitive exclusion principle, we posed the question: how can the two species coexist?…”

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“…The PFG also had in their stomach more individuals of chironomidsae and gammarids than other taxa, but this number was smaller than in the stomachs of the LFG. Salmons, trout and grayling also eat relatively abundantly crustaceans, particularly gammarids (Witkowski et al, 1984;Strandmeyer and Thorpe 1987;Amundsen and Gabler 2008,). The streams examined offer good nutritional conditions for the fry of salmonids, because of a high density of gammarids and crustaceans .…”