Procellariiformes are endangered due to by-catch, marine pollution, breeding ground loss, and
depletion of fish stocks. The Desertas Petrel (Pterodroma deserta) is one of these species,
classified as vulnerable. To assess its at-sea threats during the breeding season, several
individuals were tagged with GPS and GLS devices. The combination of both allows a detailed
assessment of their location associated with behaviour, as well as detecting interactions with
fishery vessels. Stable isotope analysis of blood samples was conducted to see trophic
differences in their diet. In addition, data of daily longline fishing effort were obtained. GPS
and GLS data revealed that P. deserta individuals forage around the Azores, foraging areas
significantly overlap with fishery grounds, and light peaks during the night, indicating
interactions with longline fishery vessels. Moreover, interacting individuals have a n elevated
δ15N value, probably caused by fishery discard and bait used as a food source. Interactions
with longline fishing vessels generate threats. Because P. deserta is K-selected, losing breeding
individuals has an adverse effect on the population. To protect Desertas Petrels at sea,
measures to reduce the threats like time shifting of the line setting and birds scaring lines
should be utilised.
