Fa. Parrish et Rs. Goto, PATTERNS OF INSULAR SHARK DYNAMICS BASED ON FISHERY BYCATCH AND LIFEGUARD SURVEILLANCE AT OAHU, HAWAII, 1983-1992, Bulletin of marine science, 61(3), 1997, pp. 763-777
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.