Depth Preference of Settling Red Drum (Sciaenops ocellatus) Larvae in Relation to Benthic Habitat Color and Water-Column Depth

Avariety of sensory cues could be operating to aid fishes in finding benthic settlement habitat. Visual cues are thought to be most important over short distances when light is adequate. Preference for substrate color (black, green, and yellow) at two water-column heights (85 and 33.3 cm) was tested on red drum, Sciaenops ocellatus, at pre-settlement, settlement, and post-settlement sizes. For settlement-and post-settlement-size classes, no effect of substrate color or water-column height was detected on mean distance of fish from the bottom or strength of depth preference. Presettlement larvae in the deep water column exhibited greater strength of depth preference than those in the shallow water column (9.6 +/- 7.1 vs. 5.6 +/- 4.1 cm 5 min(-1), respectively). Presettlement larvae were closer to the bottom in the shallow water column than the deep water column (19 +/- 9 vs. 44 +/- 28 cm). Over green and yellow substrates, they were closer to the bottom in the shallow water column compared to the deep water column (19 +/- 9 vs. 53 +/- 28 cm over green and 15 +/- 10 vs. 41 +/- 26 cm over yellow). However, no difference was detected in mean depth over the black substrate (21 +/- 8 and 39 +/- 28 cm for shallow and deep, respectively). These results suggest pre-settlement-size larvae respond to benthic cues prior to settlement by avoiding light colors of estuarine substrates and not descending toward the substrate in the presence of dark colors associated with the offshore environment.