TEMPORAL CHANGE IN FORAGING BEHAVIOR OF THE FISH CORYPHAENOIDES-(NEMATONURUS)-YAQUINAE IN THE CENTRAL NORTH PACIFIC

Deep-sea grenadier fish Coryphaenoides (Nematonurus) yaquinae were attracted to a baited free-fall video camera and tracking vehicle during 10 deployments in the central North Pacific (31-degrees-N, 159-degrees-W) at a depth of 5800 m. The mean time of arrival of the first fish was 31.0 min after landing on the sea floor. The mean number of fish within camera view increased to a peak of 5.25 at 90 min after landing and decreased thereafter. The initial arrival rate was 0.06 fish min-1, and mean fish staying time was 122 min. The staying time was much shorter than in previous work at this site, suggesting a change in food supply with time of year. Grenadiers were tracked using ingestible acoustic transmitters. The mean time until transmitter ingestion after the bait landed was 85.1 min. Fish that swallowed transmitters dispersed at radial rates of 1 to 20 cm s-1, and all had departed to a range of > 1000 m by 13 h after landing. Movements to an altitude of > 15 m were recorded for 60 % of fish tracked and occupied 12.9 % of total tracking time. Bottom current speeds were between < 1 and 9 cm s-1 with a tidal rhythmicity.