K. N. Holland á B. M. Wetherbee C. G. Lowe á C. G. Meyer Movements of tiger sharks (Galeocerdo cuvier ) in coastal Hawaiian waters Received: 26 July 1998 / Accepted: 28 April 1999 Abstract Externally and internally implanted sonic transmitters were used to track the movements of eight tiger sharks (Galeocerdo cuvier) ranging between 200 and 417 cm total length (TL), captured by hook-and-line on the south coast of Oahu, Hawaii, between 1993 and 1997. Attachment of the transmitters was facilitated by the fact that captured sharks exhibited tonic immobility when restrained and inverted at the side of the tagging vessel. Three common themes emerged from the hori- zontal movements of the tracked sharks: (1) oshore movements away from the island, (2) extended periods of directed, ``straight-line'' swimming, (3) orientation to the Penguin Banks ± a shallow bank located ' 35 km from the release point. In shallow water (<300 m) the sharks swam predominantly close to the bottom, in open water (>300 m) they swam within the mixed layer at depths of 80 m. One shark dove brie¯y to 335 m. The average estimated swimming speed of sharks traversing open water was 0.29 body length (BL) s )1 . Two sharks were recaptured after termination of the tracks; one of these sharks was recaptured twice, with a total time at liberty of 377 d. The data suggest that Hawaiian tiger sharks move within large home ranges and that they can eciently navigate between distant parts of their range, even when this requires crossing open ocean waters. Introduction In Hawaii, the long-term rate of shark attacks on hu- mans is low, averaging ' 2:0 con®rmed attacks per year over the past several decades (Wetherbee et al. 1994). Between 1958 and 1997, only three con®rmed fatal shark attacks were reported. However, two of these fatal at- tacks occurred within a 12 mo period in 1990 and 1991, and several other, non-fatal attacks occurred during the same period (Wetherbee et al. 1994). This series of at- tacks rekindled widespread public debate about the ap- propriateness and the feasibility of shark-control programs. Because most shark attacks in Hawaii are probably attributable to tiger sharks (Galeocerdo cuvier; Randall 1992), most of the discussion focused on the behavior of this species. In fact, an improved under- standing of the behavior of tiger sharks has pertinence beyond Hawaii, since tiger sharks are circumglobal in distribution and are considered one of the world's most dangerous species (Baldridge 1973; Compagno 1984; Randall 1992). Previous shark-culling programs conducted in Hawaii between 1959 and 1976 included prolonged, statewide ®shing that killed nearly 5000 sharks of several species (Tester 1969; Wetherbee et al. 1994) but, despite killing over 500 tiger sharks in these programs, there is no evidence that this widespread ®shing eort had an eect on the rate of attacks on humans in Hawaii (Wetherbee et al. 1994). Conse- quently, much of the recent debate focused on whether there are alternative methods of addressing the per- ception that unchecked shark populations pose a threat to public safety. For instance, rather than culling large numbers of sharks from throughout the region, could ®shing eort focused on a speci®c area result in a lasting, localized depletion of dangerous sharks in that area? A related question is whether ®shing for sharks at the site of an attack soon after it occurred would be likely to capture the shark re- sponsible for that attack. Marine Biology (1999) 134: 665±673 jj: jjj ± jjj Ó Springer-Verlag 1999 Communicated by M.H. Horn, Fullerton K.N. Holland (&) Hawaii Institute of Marine Biology, University of Hawaii at Manoa, P.O. Box 1346, Coconut Island, Kaneohe, Hawaii 96744, USA Fax: 001 (0)808 236-7443 e-mail: kholland@hawaii.edu B.M. Wetherbee NOAA-NMFS-NESC, 28 Tarzwell Drive, Narragansett, Rhode Island 02882, USA C.G. Lowe á C.G. Meyer Department of Zoology and Hawaii Institute of Marine Biology, Edmonson Hall, University of Hawaii at Manoa, Honolulu, Hawaii 98822, USA