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

Committee Chair

Sutton, Trent

Committee Member

Barst, Benjamin

Committee Member

Bergstom, Carolyn

Table of Contents

Chapter 1: Introduction

Chapter 2: Diet composition and variations in total mercury concentrations in fourhorn sculpin Myoxocephalus quadricornis from Prudhoe Bay, Alaska

Chapter 3: Using otoliths to establish growth curves and spatial use of fourhorn sculpin from Prudhoe Bay, Alaska

Chapter 4: General conclusions.

Abstract

Fourhorn Sculpin Myoxocephalus quadricornis is a common nearshore fish with a circumpolar distribution and high site fidelity, making this species a potential sentinel organism for detecting environmental change. Despite their abundance, Fourhorn Sculpin remain understudied in the Beaufort Sea, a region undergoing change because of a warming climate. This study examined the age structure, growth, spatial use, diet composition, trophic position, and mercury (Hg) bioaccumulation in Fourhorn Sculpin collected from Prudhoe Bay, Alaska, within the central Beaufort Sea. Stable isotope analysis (δ13C, δ15N) and Bayesian mixing models revealed a diet dominated by pelagic Mysida (posterior median proportion = 0.79). Fourhorn Sculpin muscle total Hg concentrations ([THg], mean = 56 μg∕kg wet weight) increased with fish length, age, and trophic position. Male Fourhorn Sculpin contained higher [THg] than females at similar lengths, likely influenced by dietary differences. Larger individuals, especially females, consumed more benthic Isopoda. Sagittal otoliths (N = 235) indicated that most individuals were between ages 2 and 4, with a maximum age of 11. Males were smaller and younger on average than females, and sex­ specific von Bertalanffy models showed male growth slowed after age 3 and female growth slowed after age 6. Otolith microchemistry (N = 43) revealed 87Sr/86Sr ratios consistently near the global marine value, suggesting that Fourhorn Sculpin are primarily marine residents. A few individuals exhibited higher 87Sr/86Sr ratios and lower scaled 88Sr concentrations near the otolith core, which indicated freshwater spatial use during early development. Collectively, these findings provide foundational data on the life history and Hg exposure of Fourhorn Sculpin in Prudhoe Bay.

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