SIZE-SPECIFIC SOCIAL INTERACTIONS AND FORAGING STYLES IN A SHALLOW-WATER POPULATION OF MUTTON SNAPPER, LUTJANUS-ANALIS (PISCES, LUTJANIDAE), IN THE CENTRAL BAHAMAS

Field observations quantified the effects of fish size and time of day on activity patterns, intraspecific encounters, and foraging styles i n mutton snapper, Lutjanus analis, during the spring and winter of 199 1. Fish ranged in size from 15 to 65 cm fork length (FL), and were ass ociated with an artificial patch reef system located on a shallow seag rass meadow in the Exuma Cays, Bahamas. The most common, non-resting d iurnal activities were intraspecific chasing and displacing, and feedi ng. Intraspecific displacing was significantly higher during midday co mpared to morning or evening. The highest proportion of intraspecific encounters (combined chasing and displacing events) occurred among med ium (25-35 cm FL) and large (> 35 cm FL) fish. The few large fish obse rved (13% of population) initiated the same proportion of encounters a s the predominant (50%) medium fish. The remaining (37%) small fish (> 25 cm FL) were the least aggressive. Dark barred and dark nape color patterns were associated with displacing and chasing, respectively. Fi sh exhibited considerable variability in feeding behavior. Proportiona lly fewer fish fed during midday compared to morning or evening, altho ugh small fish fed proportionally more often than medium or large fish despite time of day. Picking was the primary feeding mode and was obs erved during all times of day. Winnowing was observed during midday an d evening, whereas midwater strikes were confined to morning and eveni ng. Small fish displayed proportionally higher picking and midwater st rikes during morning and evening, respectively, compared to medium or large fish. However, large fish winnowed proportionally more often tha n small or medium fish during evening. Dark barred color patterns were associated with feeding on the substrate, whereas no color changes oc curred during midwater strikes. Our results indicate that L. analis fo rms dominance hierarchies and that high variability in foraging styles , according to fish size and time of day, may be a means to reduce int raspecific competition.