Abstract

The underlying mechanisms driving population dynamics, such as density-dependence, are not fully understood, but are important for conservationists and fisheries managers. Intercohort competition can play an important role in regulating population size. To investigate the role of intercohort competition, I completed a field experiment and a meta-analysis. In the field experiment, I examined age-class interactions and how they affected the individual growth and survival of brook trout (Salvelinus fontinalis). I manipulated the density of brook trout with three different density treatments in a Newfoundland stream: age 0+ fish only at a density of 4 fish/m2; fish aged 1 year or older (age 1+) only, at a density of 1 fish/m2; and, age 0+ fish at a density of 4 fish/m2 combined with age 1+ at a density of 1 fish/m2. The average daily growth rates and survival for age 0+ fish were lower, but not significantly so, in the presence of age 1+ fish, compared to when alone, likely due to a small sample size and a lack of statistical power. The meta-analysis showed that age 1+ fish had a significantly negative effect on the behaviour, habitat use and fitness correlates of age 0+ fish, but age 0+ fish had no significant effect on age 1+ fish. Differences in the stream habitats used by different cohorts of stream salmonids appear to be the result of intercohort competition, rather than representing different fundamental niches. The findings of the meta-analysis have implications for guiding the management of salmonid populations and their habitats.