Associative relationships, such as mutualism, commensalism, and parasitism are not often discussed in relation to sharks. We report herein on observations of associations between two teleost species and a variety of shark species in the Gulf of Mexico. These observations prompted the following questions: 1.) How common are associative relationships across different species of shark? and 2.) What benefits do the teleost associates gain from their interactions with sharks? Using underwater video, Round Scad (Decapterus punctatus) and Atlantic Bumper (Chloroscombrus chrysurus) were observed associating with both Blacktip Sharks (Carcharhinus limbatus) and Spinner Sharks (Carcharhinus brevipinna). Additionally, we observed Scad associating with Blacknose Sharks (Carcharhinus acronotus). These observations prompted an on-line image survey wherein additional un-reported associations were discovered. Eight shark species were searched online to determine the percentage of images in which the shark was associated with a teleost species. Video and image analysis consisted of identification of the shark species and the teleost associate, along with counting the abundance of associates. A qualitative assessment of school architecture and behavior was conducted for the field video.
Results/Conclusions
In the field video footage, both Scad and Bumpers were observed schooling around and swimming with the sharks. Schools of Scad ranged in size from 1 to approximately 440 individuals and had a mean size of 54 individuals. Larger schools typically formed a cloud around the shark, whereas smaller schools tended to stay posterior to the pectoral fins of the shark. From the online image survey, we determined the most common associates were Mackerel Scad (D. macarellus), D. punctatus, Sharksuckers (Echeneis naucrates), Common Remora (Remora remora), and Pilotfish (Naucrates ductor). Few of the sharks surveyed occurred with Scad, except the Great White (Carcharodon carcharias) which was associated with Scad in 50% of the assessed images. Members of the family Echeneidae were most commonly associated with different shark species, ranging from being present in 30% to 46% of the images. The most likely explanation for the association between Scad and sharks is a commensalistic relationship. In this case, the Scad could benefit from increased feeding opportunities, protection from meso-predators, or a possible hydrodynamic advantage by swimming behind the shark. To our knowledge, this is the first report of an apparent symbiosis between various shark species with Round Scad and Atlantic Bumpers.