Humpback Whale ( <scp> <i>Megaptera novaeangliae</i> </scp> ) Site Fidelity, Residency, and Movement Patterns in Ireland Based on Citizen Science Data

ABSTRACT Understanding the residency and movement patterns of large cetaceans like the humpback whale is crucial for effective conservation. In Ireland, the Irish Whale and Dolphin Group has been collecting humpback whale data since the 1990s, primarily through citizen science. This collective effort has contributed to the creation of the Irish Humpback Whale Photo‐identification Catalogue. Using this dataset, we assessed humpback whale intra‐ and inter‐annual site fidelity in Irish waters by calculating resighting rates and composite indices. Lagged identification rates and net squared displacements were used to describe residency times and movement patterns. We also modeled changes in migration timing, exploring possible phenological adaptations to a changing ocean. Humpback whales showed high site fidelity to Irish waters, with a mean interannual resighting rate of 70%, and 25% of identified individuals were resighted in five or more different years. Residency times were modeled at a minimum of 20 days, with a minimum estimated home range of 100 km. Earlier arrivals in Irish waters were significantly correlated with rising global ocean temperatures. Our study offers the most comprehensive data on humpback whale residency and movement in this region, highlighting the value of citizen science and rigorous data management for marine conservation.