The following paper has recently been published online on Blackwell Synergy and will appear in the next print issue of the Journal of Zoology. PDFs are available on request. Cheers, Peter Stevick peter@hwdt.org Stevick, PT, J Allen, PJ Clapham, SK Katona, F Larsen, J Lien, DK Mattila, PJ Palsboll, R Sears, J Sigurjonsson, TD Smith, G Vikingsson, N Oien and PS Hammond. Population spatial structuring on the feeding grounds in North Atlantic humpback whales. Journal of Zoology, London. 270:244-255. doi:10.1111/j.1469-7998.2006.00128.x Population spatial structuring among North Atlantic humpback whales Megaptera novaeangliae on the summer feeding grounds was investigated using movement patterns of identified individuals. We analysed the results from an intensive 2-year ocean-basin-scale investigation resulting in 1658 individuals identified by natural markings and 751 individuals by genetic markers supplemented with data from a long-term collaborative study with 3063 individuals identified by natural markings. Re-sighting distances ranged from <1km to >2200km. The frequencies (F) of resighting distances (D) observed in consecutive years were best modelled by an inverse allometric function (F=6631D-1.24, r2=0.984), reflecting high levels of site fidelity (median re-sighting distance <40km) with occasional long-distance movement (5% of re-sightings >550 km). The distribution of re-sighting distances differed east and west of 51W, with more long-distance movement in the east. This difference is consistent with regional patterns of prey distribution and predictability. Four feeding aggregations were identified: the Gulf of Maine, eastern Canada, West Greenland and the eastern North Atlantic. There was an exchange rate of 0.98% between the western feeding aggregations. The prevalence of long-distance movement in the east made delineation of possible additional feeding aggregations less clear. Limited exchange between sites separated by as little as tens of kilometres produced lower-level structuring within all feeding aggregations. Regional and temporal differences in movement patterns reflected similar foraging responses to varying patterns of prey availability and predictability. A negative relationship was shown between relative abundance of herring and sand lance in the Gulf of Maine and humpback whale movement from the Gulf of Maine to eastern Canada.