Analysis of tiger and white shark bycatch in the Hawaii longline fishery

Pelagic longline observer records from Hawaiʻi (1994–2025; ∼118,000 sets, ∼250 million hooks) show that tiger ( Galeocerdo cuvier ) and white sharks ( Carcharodon carcharias ) comprise an exceptionally small share of bycatch. I quantified encounter rates by sector, mapped events, tested bathymetric controls using distance to the 200 m isobath, evaluated seasonality and trends, summarized haulback condition and disposition, and benchmarked rates against other pelagic longline fisheries. Tiger sharks were recorded 173 times (deep-set tuna: 140; shallow-set swordfish: 33) and white sharks 8 times (6 shallow-set, 2 deep-set). Sectoral CPUEs were among the lowest reported globally (tiger: 0.000603–0.001500 sharks·1000 hooks⁻¹; white: 0.00000893–0.000231). Tiger occurrence probability declined with increasing distance from the shelf break, and long-term declines in tiger CPUE coincided with a progressive offshore shift in fishing locations, indicating reduced spatial overlap rather than reduced abundance. Overlap between fleet effort and the White Shark Café was minimal in both sectors. Most sharks were alive at haulback (tiger ∼88 %; white ∼80 %), and post-2000 outcomes were dominated by live releases. These results indicate extremely low interaction rates, high immediate survival, and declining exposure for tiger sharks due to shifting effort footprints; white sharks remain near-zero bycatch for biogeographic reasons. I recommend incorporating simple exposure metrics (e.g., distance to the 200 m isobath; proportion of effort near insular margins or frontal zones) into routine, sector-specific reporting to distinguish fleet behavior from abundance signals and to provide early warning if overlap increases.