Date of Award

Fall 9-23-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Ocean Science and Engineering

Committee Chair

Robert Leaf

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Eric Powell

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Wei Wu

Committee Member 3 School

Ocean Science and Engineering

Committee Member 4

Clay Porch

Abstract

In the Gulf of Mexico (GOM), Vermilion Snapper (Rhomboplites auroruben), are believed to compete with Red Snapper directly for prey and habitat. The two species share similar diets and have significant spatial overlap in the Gulf. Red Snapper are thought to be the dominate competitor, forcing Vermilion Snapper to feed on less nutritious prey when local resources are depleted. In addition to ecological pressures, GOM Vermilion Snapper support substantial commercial and recreational fisheries. Over the past decade, recreational landings have steadily increased, reaching a historical high in 2018. One cause may be stricter regulations for similar target species such as Red Snapper and Gray Triggerfish. A better understanding of the impact of ecosystem and fishery dynamics is essential for successful, long-term management of the stock. In this study, I used management strategy evaluation to assess the effectiveness of current and alternative harvest control rules (HCR) for the stock when accounting for interspecific competition and increased recreational landings. I developed an operating model that simulates the underlying population and fishery dynamics of the Vermilion Snapper stock and includes an index of Red Snapper competition. The annual competition index values were the estimated annual abundance of Red Snapper relative to the total virgin or near-virgin abundances of Vermilion and Red Snapper combined. In the second chapter, I used a random utility model to estimate the probability of a recreational angler targeting Vermilion Snapper given past management for Red Snapper and Gray Triggerfish. I incorporated the predicted targeting probabilities into the operating model from chapter one and evaluated the outcomes of the simulation. In both simulations, catch limits were set using empirical or model-based approaches. I ran 100 trials for each scenario, projected over 50 years. I found that the GOM Vermilion Snapper stock is resilient to competition and increased recreational landings, and all HCR effectively managed the stock. This study provides a methodology to incorporate interspecific dynamics into a single-species assessment model.

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