Long-term growth and movement in relation to food supply and social status in a stream fish

Long-term patterns of residency, growth, and movement among drift-feeding fish in relation to their social status and macroinvertebrate drift were determined. Each month, over 21 months, we quantified macroinvertebrate drift, fish abundance, and biomass, recorded individual fish lengths, weights, and social rank, and monitored individual diel activity of fish residing in different pools. Despite marked variation in food supply between pools, average growth rates within each pool were not significantly different. However, size and growth of the largest (dominant) fish (i.e., ones that had priority access to preferred feeding positions and times) was positively related to food supply. In contrast, the distribution and growth of smaller subordinate fish were only weakly related to the distribution of resources. Over the 21 months of study, growth rates of the first-ranked fish were high and they rarely relocated to a new pool. Second- and third-ranked fish exhibited comparatively low growth rates and relocated to new pools more frequently than fish of any other ranks (higher or lower). Movement of these fish from their original pool of residency did not always result in increased growth rates. Overall, our study demonstrates that short-term behavioral responses to spatial and temporal resource availability and intraspecific competition (i.e., social status) interact to determine long-term patterns of distribution, movement, and growth. Copyright 2009, Oxford University Press.