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11-08-2010, 02:52 PM #1
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Sneaky feeding by salmon in sympatry with dominant brown trout
By Johan Hojesjo, John D. Armstrong, Sian W. Griffiths
Animal Behaviour, Volume 69, Issue 5, May 2005, Pages 1037-1041, ISSN 0003-3472, DOI: 10.1016/j.anbehav.2004.09.007.
We compared the feeding performance and overt aggressive behaviour of two closely related salmonids occupying the same food patches. Foraging competition between pairs of Atlantic salmon, Salmo salar, and brown trout, Salmo trutta, in which trout were the larger and predicted to be the more dominant species, was investigated in a controlled stream channel environment. Trout held station by swimming actively in the central regions of food patches, whereas salmon occupied the margins, generally remaining stationary on the stream bed. There was little overt aggression, but the direction of attacks was consistent, with trout being dominant over salmon. Trout made significantly more foraging attempts (61.4% of food items presented) than salmon (28.9%). However, efficiency of food capture was higher in salmon (97%) than in trout (78%) and there was no significant difference between species in food intake. Salmon fed by briefly invading the space occupied for most of the time by trout. This behaviour has similarities to the `sneaky' behaviours often shown by subordinate male salmonids during spawning, when gametes rather than food are the contested resource.