Diving ecology of selected seabird species from the Southern and Northern Western and Central Pacific Ocean

Bycatch is a prominent driver of seabird declines globally, including in commercial pelagic longline fisheries. Seabird diving depth and speed influences the effectiveness of several bycatch mitigation methods. However, most studies of seabird diving ecology were conducted outside of the Western and Central Pacific Ocean (WCPO), despite this area being a seabird hotspot. Additionally, the WCPO encompasses different seabird species assemblages between Hemispheres, which may result in key differences in diving ecology. Herein, we present preliminary results from two field studies and synthesise all available data on diving ecology for selected seabird species within the WCPO. In the Southern WCPO, we studied the diving ecology of three Procellaria petrels by deploying time-depth recorders in New Zealand (n = 55) to assess dive depths, durations, and descent rates. Black Petrels (P. parkinsoni) dived the deepest, with a maximum depth of 38.5 meters and 25.5% of dives >10 m depth. Westland Petrels (P. westlandica) dived up to 17.3 m, with 0.6% of dives >10 m, and showed the fastest descent rates at 1 m/s. White-chinned Petrels (P. aequinoctialis) reached maximum depths of 21.7 m, with 2.1% of dives >10 m. In the Northern WCPO, we studied the diving ecology of two Phoebastria albatrosses by deploying multisensor data loggers in Hawai’i, USA., (n = 63) to assess dive depths, duration, and frequency. Laysan (P. immutabilis) and Black-footed Albatross (P. nigripes) had similar maximum diving depth of 6.0 m and 5.9 m, respectively. Deep diving behaviour was rare in both species, with only 2% of dives exceeding 2 m of depth, yet 74% of Laysan and 65% of Black-footed Albatrosses engaged in diving behaviour. Finally, the diving ecology synthesis puts these data into context and challenges the notion of fundamental diving ecology differences between Northern and Southern Hemispheres. Our results show that hooks remain accessible to depths of 20 m for Black Petrels and 10 m for Westland and White-chinned Petrels in the Southern Hemisphere, and to 6 m for albatrosses in the Northern Hemisphere. Achieving protections of hooks in line with these depths would require combinations of weighted branch lines and tori lines and night setting or hook-shielding devices to reduce bycatch to low levels.