Distinctive markings of sharks: Ethological considerations of visual function

Abstract

Behavioral reports on free-ranging sharks or those held under semifield conditions almost invariably contain a section on social activities. The frequent inclusion of such information allows the cautious suggestion that most, if not all, sharks possess the means by which requisite information is transferred between individuals so that social functions can be achieved. Such transfer could be readily accomplished through the visual modality in conjunction with appropriate optical signals, the latter being specific motor patterns and/or specific body markings. Many sharks possess body markings that likely serve as effective camouflage, particularly among those animals dwelling on or near the bottom. Distinctive markings are found, however, also on fishes that inhabit open water (pelagic) regions and it is one group of these enigmatic markings, the distinctive, fin markings of sharks within the well-known families Carcharhinidae and Sphyrnidae that forms the subject of this report. This report summarizes various functions that such markings could subserve. It focuses, then, on the more probable functions in light of correlational data relating the intensity of such markings to certain water conditions. The report concludes by considering one of the most puzzling cases of fin markings, the large white tipped “paddles” of the oceanic whitetip shark Carcharhinus longimanus. Evidence suggests that such markings are, in fact, visual lures that aid in the capture of extremely rapid moving prey.