Profitable stream positions for salmonids: relating specific growth rate to net energy gain

Abstract

A model is developed to predict potential net energy gain for salmonids in streams from characteristics of water velocity and invertebrate drift. Potential net energy gain, or potential profit, is calculated for individuals of three species of juvenile salmonids in a laboratory stream aquarium, based on the energy available from drift minus the cost of swimming to maintain position. The Michaelis–Menten or Monod model is used to describe the relationship between potential profit and specific growth rate. Potential profit was a better predictor of specific growth rate for coho salmon (Oncorhynchus kisutch) than for brook trout (Salvelinus fontinalis) or brown trout (Salmo trutta). Coho salmon always achieved higher specific growth rates than either brook trout or brown trout in concurrent experiments, and maintained growth to lower resource thresholds. In each experiment, fish established intraspecific hierarchies and dominant fish held positions affording maximum potential profit. The use of potential profit as an optimal foraging model was tested by predicting the potential for net energy gain at coho salmon positions from the overall pattern of flow and invertebrate drift in the stream aquarium, and ranking these positions from highest to lowest potential profit. This predicted ranking was nearly identical to the rank observed in the linear dominance hierarchy. The results of experiments confirm ideas of other investigators about mechanisms of microhabitat selection by stream salmonids.

Following food clouds: feeding association between a minute loricariid and a characidiin species in an Atlantic Forest stream, Southeastern Brazil

“…obs.). A high amount of preys per unit of time may be available under swift water flow (Fausch, 1984); however, the ability of some fishes to locate and catch them is lessened under this condition (Hill & Grossman, 1993), which may be possible in the case of Characidium sp. Thus, the feeding association of Characidium sp.…”

Prior residence, territory quality and life-history strategies in juvenile Atlantic salmon (Salmo salar L.)

“…Although the larger, more aggressive fish in group 1 did obtain and defend large territories, they did not appear to choose the most profitable sites in terms of water velocity and particulate drift, as has been documented before in several studies (Fausch, 1984;Grant, 1990). These earlier studies provided evidence for the assumption that higher quality individuals will obtain territories, and the best territories will belong to those of highest rank (Maynard Smith, 1974;Arcese, 1989).…”

“…Moreover, most studies are based on observations of already established territory holders, and cannot disassociate the effects of territory quality and phenotypic quality on an individual's behaviour. However, there seemed to be a distinct hierarchy within the non-territorial fish: larger fish were more aggressive and spent more time at the upstream end of the riffle (the preferred feeding site; Fausch, 1984). This relationship persisted in the absence of actual territory ownership, suggesting that increased aggression was not a consequence of larger fish obtaining territories in group 1, but a cause.…”

“…Across all groups, aggression correlated significantly with size. In salmonids, there is often a clear correlation between status and size (Jenkins, 1969), and dominant fish tend to hold the most profitable positions (Fausch, 1984). However, it is unclear whether increased aggression is a consequence of territory ownership or a cause; increased aggression on establishing a territory has been described in the competitive threat hypothesis (Dill, 1978;Abbott et al, 1985).…”

“…The study also examined which individuals obtained which territories within each group of introduced fish, given the virtually untested assumption that the best territories will go to individuals of highest rank (Maynard Smith, 1974). Although Fausch (1984) and Hughes (1992) have shown that highest ranking individuals owned territories with the highest resource level, it was unclear whether owning a high-quality territory was a consequence of dominance or its cause.…”