Direct measurement of active dispersal of food-falls by deep-sea demersal fishes

Abstract

BAITED cameras on the deep ocean floor first revealed the presence of communities of scavengers, including deep demersal fishes capable of consuming food falls and thus dispersing surface-derived organic carbon1–3. By embedding acoustic transmitters in baits and deploying them together with an automatic tracking system and cameras on the sea floor4,5, we have now tracked the speeds and directions of departing deep demersal scavenging fishes. At a series of stations between 4,000 and 6,000 m deep in the Northern Hemisphere, in contrasting trophic regimes, we have found that two closely related species of fish, Coryphaenoides (Nematonurus) armatus and C.(N .) yaquinae have a significant role in bait dispersal. Even in remote oligotrophic locations, transmitters were consumed rapidly and were removed from the area of detection at a mean velocity of 0.11 m s−1. We find that these fish are active foragers, constantly moving independently of bottom currents. This result is contrary to previous speculation of passive or drifting strategies6 which might have been expected to conserve energy in a food-limiting environment.