AVOIDANCE OF A CAMERA SYSTEM BY A DEEP-WATER FISH, THE ORANGE ROUGHY (HOPLOSTETHUS-ATLANTICUS)

The response of the benthopelagic fish, orange roughy (Hoplostethus atlanticus), to lowering an underwater camera was monitored acoustically. Acoustic layers of the fish at 660-790 m depth dispersed rapidly at least 30-40 m when the camera was approximately 130 m above them. The reaction occurred day and night and prior to activation of the strobe lights, so it was presumably mediated by the low-frequency sound of the system being lowered rather than visually. Orange roughy contain a pronounced lateral line and extensive frontal sensory canal system that may be used to sense low-frequency sound. Our observations indicate that some marine species are highly sensitive even to non-capture sampling gears, so use of non-remote methods of sampling may lead to highly biased estimates of density. The avoidance response is consistent with the relatively high metabolic levels that have been reported for this species, as well as with their very low estimated rates of natural mortality. We speculate that the response has evolved to facilitate escape from large, highly mobile predators.