Understanding how populations are regulated is an important question driving to the heart of our ability to describe population dynamics. Individual growth can be affected by both abiotic (environmental variation) and biotic (population density) factors. Stream dwelling salmonids present an ideal opportunity to explore these relationships as they inhabit a well defined environment where the community can easily be defined and competing species readily identified.  Analysis of a long term data set from the West Brook, MA, USA using generalised linear models allowed us to estimate the effect of environmental variation (stream flow and water temperature) on fresh water Atlantic salmon growth rates. Growth rates corresponding to each season were calculated for fish that were recaptured during consecutive electrofishing sampling occasions and these data were analyses using generalised linear mixed models using AIC to identify the best model describing individual growth.

Results/Conclusions

Atlantic salmon individual growth rates were highly seasonal with fastest growth occurring during spring. Our analysis found that Atlantic salmon growth rates were correlated with temperature and stream discharge with an interaction between discharge and temperature, most noticeable during summer, where high temperatures led to slower growth, but this effect was stronger when stream discharge was lower. Salmon growth rates declined with increasing salmon biomass and were also affected by the biomass of the other salmonids present in the West Brook. We found an interaction between stream discharge and biomass with the strength of the density dependent relationship affected by stream discharge.  Density dependence was strongest during spring, but the strength of the density dependent relationship declined in years with higher stream discharge. Salmon growth rates have important population dynamics consequences as the age at which they begin their seaward migration is size related, which reflects previous growth.