| Fishes associate with floating objects (e.g. branches, leaves, drift algae, jetsam) in all oceans of the world. I reviewed pertinent literature and conducted field research in the near-shore waters of the Pacific coast of Panama, Central America. Two hundred thirty-two species from 73 families of fishes were recorded as associating with floating objects from the literature. The present study recorded 26 species from 16 families associating with floating objects by direct observation and collection. Using Fish Aggregation Devices (FADs---man-made flotsam, deployed for the purpose of aggregating fishes), I determined that FAD-associated fishes exhibit aggregative behavior, clustering around objects occupied by prior recruits, probably coming from offshore sources. Smaller assemblages gained additional fishes from one day to the next, and assemblages larger than 11 individuals lost members at rates significantly different than that predicted by random recruitment. Larger FADs attracted larger and more species-diverse fish assemblages than FADs one third the size of the larger. FADs covered by fouling organisms also attracted larger and more diverse assemblages of fishes than FADs devoid of fouling organisms. Over a period of hours, FADs enriched with fish retained those fish and accumulated additional fish while FADs that began without fish failed to attract significant numbers of recruits. The literature suggests that of the drifting material common in marine environments, drift algae attracts the greatest number of fish species. Large woody debris also represents an important ecological resource in the epipelagic zones, and anthropogenic flotsam, particularly discarded fishing gear, may represent a growing resource for fishes. Some families of fishes have a disproportionate number of flotsam-associating species---these families may possess ecological attributes which predispose them towards associating with flotsam. Of the hypotheses that have been advanced to explain the association of fishes with floating objects, only two have been the subject of empirical research: flotsam as shelter from predators in an exposed environment, and the visual advantage to fishes hovering in shade. Other hypotheses have merit, but need to be tested. None of these hypotheses are mutually exclusive. |
