Does dominance status correlate with growth in wild stream-dwelling Atlantic salmon (Salmo salar)?

Abstract

Social hierarchies result in the unequal distribution of resources, with dominant individuals able to monopolize access to food, shelter, and reproductive opportunities. However, the short-term benefits of priority access to resources have not always translated into long-term benefits in terms of growth and survival. In the present study, we test whether dominant Atlantic salmon (Salmo salar) that were able to monopolize a food source in laboratory conditions had a growth advantage over subordinates in their natural stream. There was no relationship between initial size and rank, and high-ranking individuals showed no growth advantage over subordinates over a 2-month period when returned to the wild. A fish's growth rate in the wild was also unrelated to its sex or initial size, or the density of other salmon of the same age class within each experimental site. There was, however, spatial variability in growth, with salmon in one site gaining twice as much weight as did fish from the other sites. This suggests that at most of the sites, resources were limited in availability and that the absence of a relationship between growth and dominance rank was not owing simply to an excess of food being available. The lack of a positive correlation between social status and growth in the wild may be explained by several mechanisms, including the spatio-temporal variability in resources, interspecific interactions, fluctuations in habitat, or the presence of predators.