Geographical movements, site fidelity and connectivity of killer whales within and outside herring grounds in Icelandic coastal waters

Investigating the movements and site fidelity of individuals enhances our understanding of population ecology and structure. Killer whales occur around the coast of Iceland; however, information on the connectivity between different regions is limited to herring grounds, where they are observed frequently. In this study, we used photo-identification data to investigate the movements and site fidelity of whales within (South and West) and outside (Southwest, Northwest, Northeast and East) Icelandic herring grounds. Additionally, we used a 10-year photo-identification dataset in the South to investigate long-term site fidelity patterns to a single location. Of the 440 individuals sighted more than once, nearly half (48%) moved between herring grounds and site fidelity was higher within, compared to outside, herring grounds. Outside herring grounds, individuals showed: more movement from Southwest to West compare to South, indicating this region is not exclusively a passage between herring grounds; low site fidelity to the Northeast with fewer photographic matches to other regions, suggesting individuals found here may be part of an offshore population that occasionally visits the area; and low proportion of matches to other regions in the Northwest and East, although small sample sizes precluded firm conclusions. Finally, long-term residency of killer whales in the South showed dynamic patterns, likely caused by prey availability and/or environmental changes. This study elucidates the complexities of killer whale occurrence and connectivity within the North Atlantic and suggests population structure that should be further investigated for appropriate regional conservation assessments.