Phenology of harbor seal pupping and the influence of weather on pup counts, investigated by UAV

• Published in: Marine Mammal Science
• Main Authors: Seganfreddo, Samanta, Teilmann, Jonas, van Beest, Floris M., Galatius, Anders
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2023
• Subjects: behavior; breeding; phantom drone; phenology; Phoca vitulina; survey; weather variables; harbor seal
• Online Access: https://pure.au.dk/portal/da/publications/phenology-of-harbor-seal-pupping-and-the-influence-of-weather-on-pup-counts-investigated-by-uav(7f1e8e4e-a66c-4452-8cb3-15c9cd30f039).html; https://doi.org/10.1111/mms.13020; http://www.scopus.com/inward/record.url?scp=85152010061&partnerID=8YFLogxK

Surveys of harbor seals to assess pup production in Denmark are conducted at the assumed breeding season peak between 9 and 15 hr at winds <10 m/s, with no precipitation at least 6 hr before observations and at low tide in areas with a significant tidal range. Harbor seal pups can swim immediately after birth, so the fraction available for counting likely varies according to conditions. In the Limfjord, a separate harbor seal population is living in a large inlet in northern Denmark where >95% of pups are born at two haul-out sites situated 4 km apart. Drone surveys of these two haul-outs were conducted throughout the breeding seasons during 2017–2019. The effects of weather conditions and timing of surveys on counts were analyzed by generalized additive mixed models. The best-performing model included date and wind speed. Pup counts grew from the onset of the observation period and were predicted to peak on June 22. Wind speed had a linear relationship with pup counts and > 50% more pups were counted at 5 m/s than at 1 m/s. To achieve representative pup counts careful consideration of survey conditions and possibly correction for these effects are necessary.