Selective Predation by Drift-Feeding Brown Trout (Salmo trutta)

1979 ◽  
Vol 36 (4) ◽  
pp. 392-403 ◽  
Author(s):  
Neil H. Ringler
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Prey Size ◽  
Energy Content ◽  
Feeding Strategy ◽  
Invertebrate Drift ◽  
Selective Predation ◽  
Heterogeneous Distribution ◽  
Brown Trout Salmo Trutta ◽  
Dominant Characteristic

Consumption of three species of prey by brown trout (Salmo trutta) in a laboratory stream was studied during 7-d experiments. Two drift rates (5 and 10 organisms/min) and three ratios (1:1, 2:1, 5:1) of small:large alternative prey were employed. Responses to prey species stabilized after 4–6 d and 800–1200 prey captures, but no prey was completely excluded from the diet. Size-selective predation was a dominant characteristic of the response. The fish appeared to alter the area (depth) searched in response to prey density; electivity was greatest when prey densities were high. Disproportionate predation on abundant prey ("switching") was a temporary phenomenon, which may have been masked by prey size. Brown trout ultimately achieved 54–91% of a hypothetical diet in which prey are ranked in order of size (energy content). Deviations from an optimal diet may be explained in terms of a feeding strategy that deals with heterogeneous distribution of prey, as well as with the behavioral capabilities of the predator. Key words: behavior, fish, invertebrate drift, optimal foraging, predation, prey size and abundance, Salmonidae, search image, streams

Optimal prey size for stream resident brown trout (Salmo trutta): tests of predictive models

1986 ◽  
Vol 64 (3) ◽  
pp. 704-713 ◽  
Author(s):  
Eileen Bannon ◽  
Neil H. Ringler
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Prey Size ◽  
Food Resource ◽  
Handling Time ◽  
Minimum Size ◽  
Small Fish ◽  
Order Stream ◽  
Mouth Size ◽  
Brown Trout Salmo Trutta

The time required to handle different-sized prey (crickets) was measured in an artificial stream for eight wild brown trout (Salmo trutta L.) in two size classes (mean total lengths, 186 and 214 mm). Handling times (HTs) scaled by mouth size were described by an exponential equation: HT = 1 + 0.84e2.35(ps/ms) (ps, prey size; ms, predator (mouth) size). Cost curves based on handling time/prey weight were used to predict optimal prey lengths of 22 mm for small trout and 24 mm for large trout. A second model based on J. W. J. Wankowski's empirical results predicted slightly smaller optima. Physical constraints provided estimated minimum prey lengths of 2.8 and 3.2 mm for large and small fish, respectively; maximum prey lengths were 89 and 97 mm, respectively. We compared the predicted optimal prey size with the size distribution of invertebrates in drift and brown trout stomachs sampled in a second-order stream from July to September 1982. The most abundant prey sizes in the study stream were near the minimum size that can be effectively handled by brown trout. Prey of the predicted optimum size were rare, but feeding was size selective in spite of a limited food resource. The growth rates of these stream-dwelling brown trout were slower than the brown trout in other streams in this region. This may reflect diets consisting largely of suboptimal-sized prey.

Testing a model of drift-feeding using three-dimensional videography of wild brown trout, Salmo trutta, in a New Zealand river

2003 ◽  
Vol 60 (12) ◽  
pp. 1462-1476 ◽  
Author(s):  
Nicholas F Hughes ◽  
John W Hayes ◽  
Karen A Shearer ◽  
Roger G Young
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Focal Point ◽  
Three Dimensional ◽  
Size Composition ◽  
Invertebrate Drift ◽  
Intake Rate ◽  
Drift Feeding ◽  
Foraging Area ◽  
Brown Trout Salmo Trutta

We tested the assumptions and predictions of a foraging model for drift-feeding fish. We used three-dimensional videography to describe the foraging behavior of brown trout, Salmo trutta, mapped water depth and velocity in their foraging area, sampled invertebrate drift to determine length class specific drift densities, and captured trout to determine the size composition of their diet. The model overestimated the fish's prey capture rate and gross energy intake rate by a factor of two. Most of this error resulted from the fact that prey detection probabilities within the fish's foraging area averaged only half the expected value. This was the result of a rapid decrease in capture probability with increasing lateral distance from the fish's focal point. Some of the model's assumptions were accurate: equations for predicting reaction distance and minimum prey size supported reliable predictions of the shape and size of the fish's foraging area and the size composition of the diet. Other assumptions were incorrect: fish detected prey within the predicted reaction volume, not on its upstream surface as expected, fish intercepted prey more slowly than the expected maximum sustainable swimming speed, and fish captured about two-thirds of their prey downstream of their focal point, rather than upstream.

Effects of woody debris on the growth and behaviour of brown trout in experimental stream channels

1998 ◽  
Vol 76 (1) ◽  
pp. 56-61 ◽  
Author(s):  
Karl Sundbaum ◽  
Ingemar Näslund
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Woody Debris ◽  
Feeding Activity ◽  
Control Channel ◽  
Invertebrate Drift ◽  
Stream Channels ◽  
Gravel Bed ◽  
Brown Trout Salmo Trutta ◽  
Experimental Stream

We examined the effects of woody debris on the growth and behaviour of brown trout (Salmo trutta) in experimental stream channels. Two types of habitat were used in the study: a complex habitat created by placing woody debris on a gravel bed and a uniform habitat consisting of a gravel bed only. The experiment was run both outdoors with wild fish that fed on natural invertebrate drift and indoors with hatchery fish that were fed artificial food. In both treatments most of the fish lost mass. In all trials, however, the fish in the woody debris channel lost less mass than the fish in the control channel. Study of the fishes' behaviour revealed less swimming activity, less aggression, and less feeding activity in the woody debris channel than in the control channel. The results of this study indicate that the presence of woody debris decreases intraspecific competition through visual isolation, allowing fish to reduce aggressive interactions and energy expenditure.

Erratum: Optimal prey size for stream resident brown trout (Salmo trutta): tests of predictive models

1986 ◽  
Vol 64 (7) ◽  
pp. 1589-1589
Author(s):  
Eileen Bannon ◽  
Neil H. Ringler
Keyword(s):  
Brown Trout ◽  
Predictive Models ◽  
Salmo Trutta ◽  
Prey Size ◽  
Brown Trout Salmo Trutta

Energetics and survival of virgin and repeat spawning brown trout (Salmo trutta)

1998 ◽  
Vol 55 (1) ◽  
pp. 47-53 ◽  
Author(s):  
Ole Kristian Berg ◽  
Eivind Thronæs ◽  
Gunnbjørn Bremset
Keyword(s):  
Brown Trout ◽  
Specific Energy ◽  
Salmo Trutta ◽  
Energy Content ◽  
Survival Rates ◽  
Total Protein Content ◽  
Energy Expenditures ◽  
Brown Trout Salmo Trutta ◽  
Investment In Reproduction ◽  
First Time

Smaller virgin spawners of a stunted population of brown trout (Salmo trutta) had higher specific energy content than repeat spawners, indicating that once maturation has started, the trout does not completely recover from its first spawning. Males had higher amounts of total and specific energy after spawning compared with females (adjusted for length differences). The greatest energy expenditures were recorded among spawning females (specific total energy losses of about 20%, which were twice the losses of male spawners). Repeat females lost 40% of their fat content. The gonads of the females accounted for 20% of the total protein content. The loss in carcass protein and fat for the spawners was greater than the corresponding loss in visceral fat and protein. Survival rates paralleled the amounts of energy expended in reproduction. Overall survival rate of first-time spawning males (females) was about 0.90 (1.00), while the corresponding value for repeat spawners was about 0.65 (0.50). It is predicted that brown trout from a stunted population should make a relatively small investment in reproduction and thus represent a case of low investment among iteroparous fish species.

Selective predation on Cladocera by brown trout Salmo trutta L.

1979 ◽  
Vol 15 (5) ◽  
pp. 521-525 ◽  
Author(s):  
P. Fltzmaurice
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Selective Predation ◽  
Brown Trout Salmo Trutta

Functional Responses of Brown Trout (Salmo trutta L.) to Invertebrate Drift

1983 ◽  
Vol 2 (1) ◽  
pp. 45-57 ◽  
Author(s):  
Neil H. Ringler ◽  
David F. Brodowski
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Invertebrate Drift ◽  
Functional Responses ◽  
Brown Trout Salmo Trutta

The effect of brown trout (Salmo Trutta L.) on stream invertebrate drift, with special reference to Gammarus pulex L.

Hydrobiologia ◽  
1994 ◽  
Vol 294 (2) ◽  
pp. 105-110 ◽  
Author(s):  
N. Friberg ◽  
T. H. Andersen ◽  
H. O. Hansen ◽  
T. M. Iversen ◽  
D. Jacobsen ◽  
...  
Keyword(s):  
Special Reference ◽  
Brown Trout ◽  
Salmo Trutta ◽  
Gammarus Pulex ◽  
Invertebrate Drift ◽  
Brown Trout Salmo Trutta
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