Surface, Planktonic, and Benthic Foraging by Juvenile Chinook Salmon (Oncorhynchus tshawytscha) in Turbid Laboratory Conditions

Abstract

We investigated the effect of turbidity on the foraging behaviour of juvenile chinook salmon (Oncorhynchus tshawytscha) in the laboratory. We assessed visual ability by measuring the reaction distance of juvenile chinook to planktonic adult Artemia prey. Chinook exhibited a log-linear decline in reaction distance with increasing turbidity. These results were similar to those obtained by workers for other species. We also determined the effect of turbidity on the foraging rate of juvenile chinook for surface (Drosophila), planktonic (Artemia), and benthic (Tubifex) prey across a range of turbidity levels (< 1,18, 35, 70, 150, 370, 810 NTU). Foraging rates were reduced at higher turbidities for all three prey. However, for surface and benthic prey, foraging rates were also low in clear water, while highest rates were attained at intermediate turbidity levels (35–150 NTU). We suggest that increased feeding rate in turbid conditions reflects a reduced potential risk to predators.

Fish or jellies—a question of visibility?

“…3) that the light flux in the basin waters will be several orders of magnitude lower in Lurefjorden, suggesting a severe reduction in the potential for visual feeding (Giske and Aksnes 1992; Aksnes and Giske 1993; Aksnes and Utne 1997). The importance of light flux and water optics for predator-prey relations has been well documented experimentally (Vinyard and O'Brien 1976;Wright and O'Brien 1984;Montgomery et al 1989;Gregory and Northcote 1993;Thetmeyer and Kils 1995;Utne 1997) and in the field (Kaartvedt 1996;Kaartvedt et al 1996). Hence, we cannot reject the hypothesis that a much higher light absorbance in the basin water of Lurefjorden (Figs.…”

Context‐dependent planktivory: interacting effects of turbidity and predation risk on adaptive foraging

“…Previous studies of turbidity's effect on foraging by visually feeding zooplanktivorous fish have shown mixed results, with some finding negative effects (e.g., Gardner 1981, Wellington et al 2010) and others finding positive effects (e.g., Boehlert and Morgan 1985, Gregory and Northcote 1993, Miner and Stein 1993. Gregory and Northcote (1993) provided some empirical data to help understand how both sets of findings are valid, suggesting that turbidity interacts with predation risk to mediate fish consumer foraging.…”

“…Gregory and Northcote (1993) provided some empirical data to help understand how both sets of findings are valid, suggesting that turbidity interacts with predation risk to mediate fish consumer foraging. These authors even generated hump-shaped relationships between intermediate consumer foraging and turbidity in the laboratory that were quite similar to our own.…”

“…Because their hump-shaped curves were derived in the absence of predation risk, Gregory and Northcote (1993) assumed that their hatcheryreared fish consumer (Chinook salmon Oncorhynchus tshawyascha) was still perceiving risk and behaving accordingly in the laboratory. Our study clearly demonstrates the danger of such an assumption, as our hatchery-reared intermediate consumer responded differently in the presence versus absence of predator cues.…”

Impact des coupes forestières sur l'écologie des jeunes stades de vie chez la perchaude (Perca flavescens) :

“…The increase of DOC in cut lakes may have lead to higher growth rate by favouring prey detection and lowering energy costs allocated to prey searching when feeding on Daphnia spp. The enhancement of feeding with increasing turbidity may be explained by the higher detection of preys as well as an increase in feeding activity caused by a lowered risk of prédation (Gregory & Northcote 1993, Utne-Palm 2002, Shoji & Tanaka 2006b). …”