Acoustic tracking of the dispersal of organic matter by scavenging fishes in the deep-sea

Movements of the scavenging deep-sea fish Coryphaenoides (Nematonurus) armatus were tracked at depths of 2500-4800 m on the Porcupine Abyssal Plain and Porcupine Seabight in the NE Atlantic using the Aberdeen University Deep Ocean Submersible (AUDOS). The AUDOS was deployed with mackerel bait and three coded acoustic transponders (CATs) covered in mackerel flesh and each enclosed ina nylon bag. Time lapse photographs allowed identification of fish ingesting CATs and estimation of fish arrival times and staying times at the bait. The radial swimming speeds recorded were much slower than inferred in previous studies using older designs of tracking equipment.

It was found that C.(N.) armatus moved away from the bait source at an average rate of 1.05 m min(-1) and separated from one another at an average rate of 1.32 m min(-1) indicating solitary independent movement with no evidence of shoaling aggregation. The average time delay before food falls were intercepted by C.(N.) armatus in the study area was 26 min, the mean fish staying time was 115 min and the swimming time required to disperse the bait to background organic carbon density in the benthos was 46 min. Thus total time for food-fall dispersal after arrival on the sea floor was approximately 3 h.