In situ studies on deep-sea demersal fishes using autonomous unmanned lander platforms

Techniques are described for research on deep-sea fishes using in situ lander platforms equipped with cameras for imaging fishes, sonars for tracking movements and other environmental monitoring sensors. Fishes are attracted to the vicinity of the platform by bait placed within view of the camera. Over most of the world's oceans at depths greater than 3000 m the dominant scavenging fish is the grenadier Coryphaenoides (Nematonurus) armatus arriving at bait within 15-150 min depending on local population abundance. Applying an inverse square law relationship scavenger abundance can be calculated from fish arrival times. These fish show evidence of optimal foraging, staying longer at the bait if food is sparse. Ingestible acoustic transmitters embedded in baits allow tracking of fish departing from the bait source. Average radial rate of movement in the abyss is 1.75 cm s(-1) dispersing small food falls within a few hours. C. armatus in the north Pacific Ocean double their swimming speed in late summer associated with seasonal enrichment of the benthos with organic carbon. In situ techniques allow comparison of swimming performance of different species, allowing elucidation of mechanisms of niche separation in otherwise apparently similar fish. Autonomous lander platforms are proposed as an important adjunct to conventional research methods based on capture of dead specimens of fish from the wild.