Capture Success and Diet of Cottid Fishes: The Role of Predator Morphology and Attack Kinematics

Abstract

In this study laboratory experiments were conducted to test predictions of capture performance based on an understanding of the hydrodynamics of contrasting feeding modes (ram and suction feeding) and on an observed ecomorphological pattern among marine members of the temperate fish family Cottidae. Small—mouthed species that feed predominately on grasping prey (e.g., crabs, isopods, gastropods) were predicted to have low capture success on an elusive prey (shrimp) and to use kinematics more consistent with suction—feeding mechanisms; large—mouthed species that feed predominately on elusive prey (e.g., fishes, shrimp) were predicted to have high capture success in attacks on shrimp and to use ram—feeding kinematics. Laboratory experiments in which predators were videotaped in attacks on either hippolytid shrimp or cancrid crabs tested both the attack success and kinematic predictions. Small—mouthed cottid species had significantly lower attack success on shrimp (20—41% vs. 45—56%) than did large—mouthed cottids. Both groups had similar high success rates in attacks on crabs on a sand surface: 93—100% for small—mouthed species and 85—95% for large—mouthed species. Most small—mouthed cottids used attack kinematics more typical of suction feeding (e.g., shorter predator—prey distances and slower attack velocities) than did ram feeders. One small—mouthed species, Jordania zonope, used attack kinematics similar to those used by large—mouthed cottids in attacks on shrimp, and had higher capture success than other small—mouthed species, but had significantly lower capture success than large—mouthed species. All predators showed some ability to modify their attack kinematics when attacking prey with different escape tactics, but cottids showed little intraspecific variation in attack kinematics, in contrast to several recent studies of the strike mechanics of lower vertebrates. These results emphasize the importance of both mouth morphology and attack kinematics in determining interspecific differences in capture success and, perhaps, diet. The success of the simple predictions presented here provides hope that general predictions of foraging ecology may be derived from morphological patterns when the prey are treated not by their taxonomic affinities but by the functional demands they make on their predators.