Date of Award

Spring 3-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Ocean Science and Engineering

Committee Chair

Dr. Eric Powell

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Dr. Wei Wu

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Dr. Zachary Darnell

Committee Member 3 School

Ocean Science and Engineering

Committee Member 4

Dr. Roger Mann

Committee Member 5

Dr. John Klinck

Abstract

Arctica islandica (ocean quahog) is the longest-lived bivalve on Earth. Individuals on the deep continental shelf of the Mid-Atlantic (US) can survive for centuries, and when found in the colder, boreal waters of Iceland, ages over 500 years can be reached. The ocean quahog is important in the US, yet very little is known about the resiliency of the ocean quahog stock to fishing activity, and ocean quahog recruitment patterns over time. To quantify and constrain age-reader error prior to age analysis, a triple-method error protocol was developed for A. islandica that included age-reader bias, precision, and error frequency. The error protocol was implemented for samples collected in 2017 from Georges Bank (GB) and Long Island (LI) in the US Mid-Atlantic. Assumptions of prolonged lapses in recruitment were not substantiated for either the GB or LI populations, yearly cohorts were observed for the past century, and both populations presented recruitment pulses in regular 8-y periods. The oldest animal at GB was a 261-year-old male, and the oldest animal at LI was a 310-year-old male. Estimated ages from this study are older than previously reported for the US Mid-Atlantic. Total mortality was higher at GB than LI, and higher for GB females than GB males. Constructed ALKs were reliable but not interchangeable between sexes or populations. The population sex ratio at GB was 1.1.1 (F:M), whereas LI was 1:1.4 and relatively deficient in fishery-sized females. The Modified Tanaka growth model was the best fit growth function for A. islandica age-length data from the Mid-Atlantic, and growth models changed over time dependent on birth year. Indexed growth from both populations expressed significant 31-y frequency periods, where GB growth lagged behind LI between 1760-1950. Growth rates of A. islandica from both populations have continuously increased since the mid-1800s, female growth rates are faster than males, and growth rates at GB are generally faster than those at LI. Females dominated large size classes, males dominated small size classes, and evidence strongly suggests that this species is sexually dimorphic.

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