Data from: Dispersive migration of breeding Juan Fernández Petrels Pterodroma externa across the eastern Pacific Ocean and overlap with tropical tuna fisheries

Abstract

Tropical seabirds often forage facultatively in association with tuna and may be affected by industrial fisheries both directly through bycatch, and indirectly through reduced prey availability following tuna removal. We tracked seven Juan Fernández Petrels Pterodroma externa – endemic to the Juan Fernández Islands, Chile, and among the most abundant seabirds in the eastern tropical Pacific – using geolocator-immersion loggers over 2 years (2020–2022) to examine migratory routes, year-round distributions, activity patterns and overlap with fisheries. During pre-laying exodus and incubation, birds occupied subtropical and sub-Antarctic waters in the southeast Pacific, reaching 5,781 and 4,298 km from the colony, respectively. During the non-breeding period, birds dispersed widely across the eastern and central Pacific, from Peru to Mexico and as far north as Hawai‘i. Individuals showed annual consistency in migration strategies but did not aggregate in a single region, with 3–8 residency periods each lasting 15–80 days. Return migrations followed looping routes through the South Pacific, likely assisted by mid-latitude westerly winds. At-sea flight activity was lower during non-breeding (45% time flying) than breeding (73–77%) and increased around the full moon, both by night (by 20%) and day (51%), suggesting lunar effects on prey availability and nocturnal foraging, and potential diurnal compensation. Although our sample was small, there was substantial overlap between non-breeding distributions and industrial tuna longline and purse-seine fisheries. These results provide the first description of their annual movements and highlight potential fisheries exposure, laying groundwork for future studies to quantify population-level distributions and the dynamics of seabird-fisheries interactions.