Differential effects of turbidity on prey consumption of piscivorous and planktivorous fish
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چکیده
Contrast degradation theory predicts that increased turbidity decreases the visibility of objects that are visible at longer distances more than that of objects that are visible at short distances. Consequently, turbidity should disproportionately decrease feeding rates by piscivorous fish, which feed on larger and more visible prey than particle-feeding planktivorous fish. We tested this prediction in a series of laboratory feeding experiments, the results of which indicated that prey consumption by two species of planktivorous fish (juvenile chum salmon (Oncorhynchus keta) and walleye pollock (Theragra chalcogramma)) is much less sensitive to elevated turbidity than piscivorous feeding by sablefish (Anoplopoma fimbria). Planktivorous feeding in the turbidity range tested (040 nephelometric turbidity units (NTU)) was reduced at high light intensity, but not at low light intensity. Comparatively low (510 NTU) turbidity decreased both the rate at which sablefish pursued prey and the probability of successful prey capture. These results suggest that turbid environments may be advantageous for planktivorous fish because they will be less vulnerable to predation by piscivores, but will not experience a substantial decrease in their ability to capture zooplankton prey. Résumé : La théorie de la dégradation des contrastes prédit quune turbidité accrue décroît plus la visibilité dobjets qui sont visibles à de plus grandes distances que celle dobjets visibles à de courtes distances. En conséquence, la turbidité devrait faire décroître de façon disproportionnée les taux dalimentation des poissons piscivores qui se nourrissent de proies plus grandes et plus visibles par comparaison aux taux dalimentation des poissons planctonophages qui se nourrissent de particules. Une série dexpériences dalimentation en laboratoire nous a permis de vérifier cette prédiction : la consommation de proies de deux espèces de poissons planctonophages, de jeunes saumons kéta (Oncorhynchus keta) et des goberges de lAlaska (Theragra chalcogramma), est beaucoup moins affectée par une augmentation de la turbidité que la consommation de poissons par des morues charbonnières (Anoplopoma fimbria). Dans la gamme des turbidités étudiées (040 unités néphélométriques de turbidité, NTU), lalimentation des planctonophages est réduite aux fortes intensités de lumière, mais non aux intensités faibles. Des turbidités relativement faibles (5 10 NTU) entraînent une réduction du taux de poursuite ainsi que de la probabilité de capture des proies chez la morue charbonnière. Ces résultats semblent démontrer quun environnement turbide peut être avantageux pour les poissons planctonophages parce quils y sont moins vulnérables à la prédation par les poissons piscivores, sans que leur capacité à capturer des proies zooplanctoniques ne soit substantiellement réduite. [Traduit par la Rédaction] De Robertis et al. 1526
منابع مشابه
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