Meeting Abstract
All native fishes living in Hawaiian streams are amphidromous, meaning that larvae hatched in streams are swept to the ocean and must migrate back upstream to reach adult habitats. The Hawaiian sleeper, Eleotris sandwicensis, is the primary predator on these migrating juveniles. Sleepers are ambush predators that lie on the stream bottom until bursting into motion to attack passing prey. Recent studies of the escape behavior of a common prey fish for sleepers, juveniles of the goby Sicyopterus stimpsoni, indicated that prey fish may be more vulnerable to attacks from the front as they migrate upstream, because pressure waves from an attacking fish might be masked by surrounding water flow. However, predatory performance of sleepers has only been measured in a lab setting without the influence of stream flow. To determine how sleepers attack prey in the wild, we recorded 42 hours of video from an array of four GoPro cameras mounted underwater in areas of Hakalau Stream (Big Island of Hawai’i) where sleepers and migrating gobies are abundant. In addition to observing predatory strikes on juvenile gobies, we also recorded sleepers striking at other sleepers. None of these resulted in the capture of a sleeper by another, but did result in smaller sleepers being driven away by larger ones. Analyses of motion patterns found no correlation between angle of attack and peak escape angle for attacks by E. sandwicensis on either gobies or other sleepers. These results are consistent with the conclusion that, if an attack can be detected, responses by juvenile gobies and sleepers may be a fixed action pattern that is not modulated in response to variation in stimuli.
