Individual variation in spawning migration timing in a salmonid
fish---exploring roles of environmental and social cues
Abstract
1. Describing and explaining patterns of individual animal behaviors in
situ, and their repeatability over the annual cycle, is an emerging
field in ecology owing largely to advances in tagging technology. 2. We
describe individual movements of adult Sakhalin taimen Parahucho
perryi, an endangered salmonid fish, in the headwaters of a river in
northern Japan during the spring spawning season over two years. 3.
Migration timing, separated into stages prior to, during, and following
the spawning period, was found to be more consistent and repeatable for
females than males. 4. We hypothesized that the observed coordinated
movement within seasons, and repeatability in migration timing across
seasons, could result from 1) individual-specific responsiveness
resulting from endogenous, biological traits that are mediated by
environmental factors, or 2) social interactions among comigrating
individuals. 5. We found that water temperature and water level
experienced by fish near the river mouth approximately a week before
arrival at the spawning ground explained variability in run timing
between years for females but not males. 6. We found no evidence of
conspecific attraction or repulsion resulting from social interactions
among the spawners and post-spawners. 7. We conclude that
individual-specific responsiveness to environmental cues was the likely
mechanism underpinning the observed migration timing and movement
patterns. 8. Determining the importance of these environmental and
social factors not only during spawning but also during non-breeding
life-history stages would contribute to a more comprehensive
understanding of migratory connectivity in this species.