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Durham University

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Publication details for Dr Sean Twiss

Pomeroy PP., Twiss SD. & Matthiopoulos J (2005) (2005). Associations of breeding grey seals persist at sea. 16th Biennial Conference on the Biology of Marine Mammals, San Diego.
  • Publication type: Conference Proceeding

Author(s) from Durham


Concurrence of at-sea movements may result from seals responding similarly to oceanographic conditions, copying “public information” from conspecifics or coherence within social units. Here we examine post-breeding movements of five groups of four grey seal mothers which pupped at North Rona (Scotland) in 2003 and were classified as “associated” (birth dates within 9d and pupping within 20m) during lactation. We test whether these individuals maintain greater cohesion at sea than individuals from the same breeding locations amongst whom there is no evidence of a social relationship. Post breeding movements were monitored with SPOT-3 satellite tags (Wildlife Computers), providing locations until tag failure around moult (4-76 days after application, median = 51). Post-breeding associations were defined initially as locations falling within 10 km in a 12 hr window. Spatial overlap of tracks within groups occurred at sea and at haul-outs in Groups 2,3,4 and 5. Pairwise associations occurred in 22/25, 44/59, 13/49 and 14/70 possible days and 3-way associations occurred in 1/8, 10/51, 0/43 and 0/66 possible days in groups 2,3,4, and 5 respectively. No 4-way associations were observed beyond the breeding site. Within-group associations continued up to 64 days after tag application but some were much more likely than others. We conclude that concurrence of movements occurred in 2/5 test groups (p<0.05). Existing models of foraging, habitat use and population change explicitly ignore social effects and may be inadequate or even erroneous for real populations, making assessment of the nature and extent of such phenomena essential.