Diverse juvenile life-history behaviors

Sockeye salmon demonstrate extraordinarily diverse life-history strategies, with individuals balancing trade-offs in growth and reproductive opportunity with risks of predation and competition throughout their life-cycle.  This diversity is widely appreciated at the scale of years, with different populations spending more or less time in freshwater and saltwater before spawning.  However,  life-history diversity within single populations has been less well studied.

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Our paper examining the diversity of juvenile life-history behaviors within a single population of sockeye salmon has recently been published in Ecology of Freshwater Fish.  We examined the life-history behaviors of adult sockeye salmon that had survived to spawn in the Alec River.  Otoliths (ear bones) provide a chronological record of an individual’s age, growth, and the environmental conditions to which it was exposed.  We examined the microchemical signatures of the otolith to determine how much growth was accumulated in the different rearing lakes of the Chignik River watershed.

Black Lake, in the upper watershed, is a shallow, warm and highly productive lake that supports rapid growth for juvenile sockeye salmon.  All sockeye salmon juveniles that rear in Black Lake eventually migrate downstream to Chignik Lake, a deep, colder and less productive lake that also supports different populations of sockeye salmon from the lower watershed.  Previous research found that earlier migrants to Chignik Lake were smaller, and in poorer condition, suggesting that these individuals would be less likely to survive to reproduction.  However, our analyses determined that Black Lake contributed to only about half of the juvenile freshwater growth on average for this population, and that 47% of individuals accumulated at least half of their juvenile growth in Chignik Lake or Chignik Lagoon.  Additionally, we detected an unexpected life-history behavior in which juveniles from the upper watershed move downstream quickly to the estuarine Chignik Lagoon and rear in brackish to saltwater for the summer prior to migrating back upriver to freshwater to overwinter.

Overall, the analysis revealed the broad diversity of life-history behaviors that contribute to a single spawning population of sockeye salmon.  In certain environmental conditions, one of the strategies may be more successful than the others, but it may fare less well under alternative environmental conditions.  The presence of these diverse viable life-history behaviors may buffer the population against extreme poor conditions in any single rearing environment.

Walsworth TE, Schindler DE, Griffiths JR, Zimmerman C (2014) Diverse juvenile life-history behaviors contribute to the spawning stock of an anadromous fish population. Ecology of Freshwater Fish. DOI: 10.1111/eff.12135

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