Use of a Rock As an Anvil for Breaking Scallops by the Yellowhead Wrasse, Halichoeres Garnoti (Labridae)
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NOTES BULLf:.TIN OF MARINE SCIENCE, 57(2): 548-549. 1995 USE OF A ROCK AS AN ANVIL FOR BREAKING SCALLOPS BY THE YELLOWHEAD WRASSE, HALICHOERES GARNOTI (LABRIDAE) James A. Coyer The use of rocks to break open or dislodge food items has been reported in several species of birds, marine mammals, and primates (Alcock, 1972; Riedman and Estes, 1990). For example, sea otters routinely crack open hard-shelled prey by striking the prey against rock anvils placed on their chest (Riedman and Estes, 1990) and wrens and song thrushes strike large insects and snails against hard objects prior to ingestion (Sibson, 1975). Such behavior constitutes tool-use, which is the "manipulation of an inanimate object, not internally manufactured, with the effect of improving the animal's efficiency in altering the position or form of some separate object" (Alcock, 1972). Among fishes, the use of rock anvils to break open prey items occasionally has been noted in select species of labrids. Working in the Red Sea, Fricke (1973) observed L'1ewrasses Cheilinus trilobatus and Coris angulata capture sea urchin prey, return to their territories with the urchins, and smash the urchins against a particular stone within their territory. Similar observations of tool-using have been noted for Thalassoma lutescens and other Thalassoma species for urchin and mollusk prey, both in aquaria and under natural conditions (tropical Pacific) (Hei- ser, 1981). The present note details the use of a rock anvil by the yellowhead wrasse, Halichoeres garnoti, in the western tropical Atlantic, thereby extending the behavior taxonomically and spatially. During a mid-morning dive on 22 October 1994, I observed a male yellowhead wrasse breaking an unidentified scallop (Pectinidae) into smaller pieces by grasp- ing the scallop in its mouth and striking it several times against a rock of terrig- enous origin. The event occurred at the Pinnacle station near the Aquarius Un- dersea Laboratory on Conch Reef off Key Largo, Florida. Water depth was 20 m, visibility was in excess of 20 m and temperature was 29°C. My attention was drawn initially to a large male (ca. 150 mm TL) and four or five smaller yellowhead wrasses (ca. 75-100 mm TL) which were feeding in an area of Halimeda sand amongst the sponges and corals. After approximately 1 min of observation, the large male grasped a scallop at the hinge, which was approximately six times wider that the wrasse's mouth width. The male then made a single violent thrashing motion against a rock which broke three small pieces from the scallop shell. The larger and central portion of the shell, which contained the bulk of the tissue, was retained in the wrasse's mouth. A few seconds later, another thrash against the same rock broke off additional pieces and dislodged the scallop from the wrasse's mouth. The large male ignored the smaller pieces, which were rapidly investigated by the smaller wrasses, and retrieved the larger central portion of the scallop. The scallop was still too large to swallow and the scallop-smashing behavior was repeated against the same rock 4 or 5 additional 548 NOTES 549 times. Whenever the central portion was dislodged from the wrasse's mouth, it was rapidly retrieved. In all cases, the wrasse made a right-ward motion into the rock to break the shell. After the last smash, the central portion of the scallop was dislodged and tissue and small pieces of the shell were swallowed. The whole event occurred over a 3 to 4 min period. Sporadic observation of the species and the area over the next 3 days revealed no similar behavior. Yellowhead wrasses are omnivorous, feeding primarily on crustaceans, ophiu- roids, and gastropods, which collectively comprise over 70% (volume) of their diet (Randall, 1967). No pectinids were present in any of the 14 fish examined by Randall (1967). Although use of a rock anvil by a yellowhead wrasse extends the behavior within the Labridae and, along with the water-directing behavior of archer fish (Toxotes spp.), represent the only examples of tool-using in teleost fishes, the observation is potentially more important ecologically than ethologically. The behavior allows yellowhead and other wrasses to utilize prey that are larger than can be ingested whole and/or more robust than can be ingested by using repeated bites to reduce prey size. If this behavior can be learned by congenerics or con- specifics in an area, the impact on certain prey groups could be significant. As male wrasses often are surrounded by a number of smaller females, it is of interest to determine if this close association is sufficient to facilitate learning by obser- vation. ACKNOWLEDGMENTS The expert assistance of S. Miller and all support personnel associated with the Aquarius Undersea Laboratory and Mission 9419 is gratefully appreciated. I thank also C. Smith and L. Walters for their support, N. Crane and G. Bernardi for diving assistance, and D. Steller for comments on an earlier draft. LITERATURE CITED Alcock, J. 1972. The evolution of the use of tools by feeding animals. Evolution 26: 464-473. Fricke, H. W. 1973. Behaviour as part of ecological adaptation. In situ studies in the coral reef. Helgolander Wiss. Meeresunters 24: 120-144. Heiser, J. B. 1981. Review of the labrid genus Thalassoma (Picses: Teleostei). Ph.D. Dissertation, Cornell Univ. 280 p. Randall, J. E. 1967. Food habits of reef fishes of the West Indies. Stud. Trop. Oceanogr. Miami No. 5: 665-847. Riedman, M. L. and J. A. Estes. 1990. The sea otter (Enhydra lutris): behavior, ecology, and natural history. U.S. Fish Wildl. Ser., BioI. Rep. 90(14). 126 p. Sibson, R. B. 1975. Rock wren using an anvil. Notornis 21: 305. DATEACCEPTED: February 3, 1995. ADDRESS: Department of Biology, University of California-Los Angeles, Los Angeles, California 90024. CORRESPONDINGADDRESS: Hopkins Marine Station, 101 Oceanview Blvd., Pacific Grove, California 93950..