Food-search strategy in ling (Molva molva L.): crepuscular activity and use of space

The activity rhythm and use of space in the food-searching behaviour of lin g (Molva molva L.) were studied by means of a stationary positioning system . Thee system consisted of a fixed array of three hydrophones, which monito red the position of each individual being tracked once every three minutes. Five ling were tagged in situ by allowing them to ingest a transmitter wra pped in bait and were tracked continuously for 6 to 11 days. Ling showed a crepuscular activity rhythm with higher levels of swimming activity at dawn and dusk. The fish occupied a home range throughout the study, and during inactive periods (about 65% of the time) they remained within a small core area. Most of the time spent outside the core area was during the period of high activity at dawn. Food-search behaviour was studied by setting macker el-baited fishing gear in the experimental area. When baits were present, l ing moved more slowly and within a more limited area, indicating area-restr icted searching in the presence of a food odour. Ling responded to and loca ted baits in both their active and inactive periods during the day, but wer e not observed to react at night. Comparing these findings with those from similar tracking experiments on cod (Gadus morhua L.) suggested that ling a re less active at night and show a more restricted use of space by occupyin g a core area. This may reflect different feeding strategies between these gadoid species with ling taking a higher proportion of mobile prey and bein g more dependent on visual stimuli. (C) 2000 Elsevier Science B.V. All righ ts reserved.