Hatcheries, phenology, and families: Juvenile steelhead ecology in Forks Creek, Washington

Abstract

Juvenile ecology can affect subsequent population dynamics. This work focuses on two aspects of juvenile steelhead (Oncorhynchus mykiss) ecology: 1) tradeoffs between naturally-spawned hatchery and wild fish, and 2) the distribution of family groups on the landscape. In Chapter 1, we compared abundance, body condition, and geographic distribution of steelhead fry in a system where hatchery-origin steelhead have been bred to spawn about four months earlier than wild-origin fish. We assigned naturally-spawned steelhead fry to hatchery, wild, or hybrid lineages using a panel of 96 single-nucleotide polymorphisms. The observed mixture proportions were 0.005 hatchery-, 0.313 hybrid-, and 0.682 wild-lineage fish. We hypothesized that the low abundance of pure hatchery-lineage fry may be due to a mismatch between the timing of breeding by the parents and suitable river conditions, resulting in low survival and physical displacement from the system. The second chapter focuses on the capacity for kin selection in juvenile steelhead. Laboratory work has established the capacity for kin-biased behavior, but field studies have been less conclusive regarding whether juvenile salmonids have the opportunity to interact with siblings in the wild. Here, we tested the null hypothesis that siblings are distributed randomly across the landscape. Pedigree analysis was performed in COLONY2 to identify full-sibling groups. Spatial autocorrelation analysis revealed that individuals less than 1 km apart were more genetically similar than expected by chance. Siblings were generally too far apart to interact, but not exclusively: in 18 out of 53 large family groups containing 5 or more individuals, the median distance between individuals was 0 m. We conclude that juvenile dispersal is prominent during the first four months after emergence. We suggest that future research focus more on the conditions and characteristics of siblings that do aggregate versus those that disperse over large or short distances.