PATTERNS OF INSULAR SHARK DYNAMICS BASED ON FISHERY BYCATCH AND LIFEGUARD SURVEILLANCE AT OAHU, HAWAII, 1983-1992

Incidental shark sightings recorded by beach lifeguards and records of shark bycatch from fishery catch reports were evaluated as possible l ong-term indices (1983-1992) of insular shark dynamics. The daily life guarding of the 17 Oahu beaches provided a documentation of effort not available from fishery data. Identified seasonal and spatial trends i n shark sightings were found to persist through successive years of su rveillance and were roughly consistent with distributions of fishery b ycatch. However, it was possible to attribute shark bycatch to changes in accessibility of fishing grounds and size of the fishing fleet. An evaluation of the potential biases in lifeguard data indicated that v ariables such as wind/surf conditions and beach attendance did not gov ern the frequency with which sharks were reported. Summer increases in sightings coincided with shark pupping activities, and winter pulses were roughly associated with periods of increased rainfall. Relationsh ips with coast and season were evident, with significantly more sighti ngs on the island's leeward coast. A survey of shark-related news stor ies compared with reports of shark sightings suggested that shark sigh tings increased on a limited scale with high media exposure. No consis tent trend in abundance of sharks was detected over the full 10-yr per iod. The interannual pattern of shark sightings (scaled for effort) re mains unexplained, despite comparison with fishery data, island runoff , sea-surface temperature, and known El Nino events.