Table of Contents
ISRN Ecology
Volume 2011 (2011), Article ID 915239, 7 pages
Research Article

Life History Tactics in Cohorts of a Partial Migratory Brown Trout (Salmo trutta L.) Population

1Department of Biology, Karlstad University, 651 88 Karlstad, Sweden
2Department of Environmental Affairs, Aquatic Ecology, County Administrative Board of Scania, 205 15 Malmö, Sweden

Received 22 June 2011; Accepted 11 August 2011

Academic Editor: D. Pimentel

Copyright © 2011 Ivan C. Olsson and Larry A. Greenberg. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


We monitored temporal changes in body size for three cohorts of a partial migratory, lake-migrating brown trout population. We tested if body mass differed between nonmigratory males, migrants, and other members of the cohort (females and immature males). We hypothesized that large-sized individuals would mature as nonmigratory males or migrate at younger ages than small-sized individuals. As previous studies have shown that female fecundity is influenced by body size and that more trout from the downstream section (D) of the stream migrated than from the upstream section (U), we hypothesized that there would be a greater proportion of mature males in D than U. We found that body size of males that reproduced was similar to migrants that migrated the subsequent spring and larger than other cohort members. Reproducing males had a larger body size than equal-aged males that delayed reproduction. Similarly, individuals that migrated had a larger body size than equal-aged individuals that migrated subsequently. The proportion of mature males was greater in D than in U. The fact that body size differentiation occurred late in ontogeny and that age of maturation and migration varied within cohorts suggests that the decision to mature or migrate might be conditionally dependent.