|Document Type:||Journal Article|
|Title:||Juvenile steelhead distribution, migration, growth, and feeding in the Columbia River estuary, plume, and coastal waters|
|Author:||Elizabeth A. Daly, J. A. Scheurer, Richard D. Brodeur, Laurie A. Weitkamp, Brian R. Beckman, Jessica A. Miller|
|Journal:||Marine and Coastal Fisheries|
|Keywords:||steelhead,Estuary dynamics,ocean ecology,hatchery and wild,feeding,growth|
Relative to the extensive research on the freshwater stage of steelhead (Oncorhynchus mykiss), there has been little research onis known about the estuarine and early marine phases of juvenile steelhead despite the decline of numerous steelhead populations including several from the Columbia River. Understanding the estuarine and ocean ecology of steelhead smolts may assist in the restoration of these populations. We analyzed distribution, diet, and growth data of juvenile steelhead collected during Columbia River estuary and ocean surveys conducted during in May, June, and September from, 1998 and 2011and examinedto 2011. We evaluated differences between fish caught in the Columbia River estuary and ocean, and between hatchery (marked) and potentially wild (unmarked) fish. Almost all of the juvenile steelhead caught in the ocean were caught duringin the May surveys (96%). Juvenile steelhead were consistently caught at our westernmost stations (>55 km from shore) indicating that we are sampling the innermost part of their distribution.they were distributed further offshore. Based on otolith structure and chemistry, we determined that the juveniles had been in marine waters an average of only 10 days (±11), and a) when collected. A portion of the steelhead that had been in marine waters less than 3three days were captured at the westernmost edge of our survey transects. indicating a very rapid offshore migration. Estuary-caught fish, particularly of hatchery origin, ate few prey taxa and consumed very little food relative to ocean-caught fish. Ocean-caught steelhead ate a wide variety of prey including juvenile fishes, euphausiids, and crab megalopae. Estuary and ocean unmarked fish had higher feeding intensities and fewer empty stomachs than hatchery fish, and were in better condition. Growth hormone levels (IGF-1) of unmarked and hatchery fish varied annually, with unmarked fish having slightly higher overall values. In general, ocean-caught steelhead increased in fork length, condition, stomach fullness, and IGF-1growth hormone levels increased in the ocean-caught fish as they moved offshore. JuvenileUnlike other juvenile salmon species, steelhead appear to quickly migrate westward from their coastal rivers, and showed patterns of increased feeding and growth in offshore waters. Understanding the estuarine and ocean ecology of steelhead smolts may assist in the management of these populations.
|Theme:||Recovery, Rebuilding and Sustainability of Marine and Anadromous Species|
Characterize vital rates and other demographic parameters for key species, and develop and improve methods for predicting risk and viability/sustainability from population dynamics and demographic information.