| Two primary ideas have been proposed on the function of a deep body morphology, based on biomechanical theory: (1) enhanced maneuverability, and (2) protection from gape-limited predators. To discriminate between these two hypotheses, I examined the behavior and performance of four sympatric coral reef fish species while maneuvering and during predator-prey interactions. Four species were selected based on body and fin morphologies: (1) foureye butterflyfish (deep body, low aspect ratio (AR) pectoral fins); (2) beaugregory damselfish (intermediate depth, low AR); (3) ocean surgeonfish, (intermediate depth, high AR); and (4) bluehead wrasse (shallow depth, high AR). Aspect ratio is defined as fin length/width. The lizardfish, a common ambush predator, was used in the study.; Research was conducted in the field (St. Croix, U.S. Virgin Islands) and laboratory during the summers of 1995-96. The maneuverability study examined turning radius, velocity and behavior while feeding. The gape-limitation study examined the differential use of anti-predator behaviors (predator inspection, bobbing).; I predicted that if a deep body morphology enhanced maneuverability, then butterflyfish should show superior maneuverability compared to the remaining three species. If a deep body morphology provided protection from gape-limited predators, I expected butterflyfish to: (1) minimize their use of anti-predator behaviors, and/or (2) exhibit the riskiest use of anti-predator behaviors.; The results indicated no evidence for the enhanced maneuverability hypothesis, but support for the gape-limitation hypothesis. Butterflyfish and damselfish, the species with deep and intermediate body depths, respectively, were superior maneuverers compared to surgeonfish or wrasse. Since butterflyfish and damselfish both had low AR pectoral fins, pectoral fin morphology appears more critical to maneuverability.; In contrast, butterflyfish did not show statistically significant changes in their behavior, while wrasse decreased the proportion of swimming behavior, and added predator inspection and bobbing in the presence of the predator. Inspection distances were greatest in the wrasse, indicating risk-averse behavior. Finally, wrasse were the only species to exhibit bobbing behavior, which is shown to be a predator perception advertisement/pursuit-deterrent. Thus, the morphological defense of a deep body morphology was the most important defense for butterflyfish, while anti-predator behaviors were the most important defenses for wrasse. |
