Date of Award

12-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Degree Statement

Master of Science in Fisheries

Department

Department of Fisheries

Granting Institution

University of Alaska Fairbanks

Committee Chair

Seitz, Andrew

Committee Member

Westley, Peter

Committee Member

Armstrong, Jonathan

Table of Contents

Chapter 1: General introduction

Chapter 2: Title

2.1 Abstract

2.2 Introduction

2.3 Methods

2.3.1 Study system

2.3.2 Study design

2.3.3 System hydrology relative to in-season climate conditions

2.3.4 Temperature and water quality sampling

2.3.5 Prelagic and benthic invertebrate sampling

2.3.6 Enclosure vs. free-swimming diet comparison

2.3.7 Assessment of stream temperature, invertebrate density and phenology by habitat

2.3.8 Assessment of growth rate specific to site and hydrology type

2.4 Results

2.4.1 Stream hydrology, physical, and biological sampling

2.4.2 Habitat-type specific invertebrate resources and salmon diet

2.4.3 Enclosure salmon growth rate across habitat types

2.5 Discussion

2.5.1 Off-channel habitats contribute to growth

2.5.2 Factors that may or may not influence growth

2.5.3 Intermittent habitats, nameless creeks and dry channels

2.5.4 Experimental design insights, management and conservation

2.6 References

Chapter 3: General conclusions

Abstract

Pacific salmon (Oncorhynchus spp.) rely on diverse freshwater habitats to complete their lifecycle. Within Alaska’s short summer season, juveniles use a complex mosaic of habitats that vary in quality across space and time, but the patterns of habitat use in large complex watersheds are poorly known and difficult to document. To evaluate how habitat conditions of hydrology types influence juvenile performance, I conducted an in-situ enclosure experiment in the Fox River watershed of Kachemak Bay, Southcentral Alaska, measuring age-0 coho salmon (Oncorhynchus kisutch) growth across four hydrologic types: a glacial and snow-fed natal creek, a groundwater-fed natal creek, a non-natal intermittent surface-fed creek, and a tidally influenced estuary channel. Growth varied significantly across sites, despite generally similar prey conditions. Intermittent surface-fed water sources supported higher growth rates, with similar thermal ranges and drift invertebrate densities. Despite similar invertebrate densities, the groundwater-fed sources yielded lowest growth, which was likely constrained by cooler temperatures that reduced foraging efficiency of coho salmon and lowered their metabolism. Estuary fish initially grew, but late-season hydrologic isolation produced prolonged temperatures above 25°C, likely inducing heat stress and reducing feeding activity as drift resources reduced to near zero, and growth stopped. These results suggest growth is shaped by an interaction between thermal conditions, prey density, and hydrologic conditions, rather than temperature alone. Intermittent habitats provide short-lived, but productive foraging opportunity, and protecting transient habitats helps maintain a more complete feeding mosaic and improve rearing opportunities for juvenile Pacific salmon.

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