Date of Award

Summer 5-2023

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

School

Ocean Science and Engineering

Committee Chair

Robert Leaf

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Kim De Mutsert

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Amy Schueller

Abstract

The Gulf menhaden stock is the target of a large commercial fishery in the Gulf of Mexico. To address the needs of both the stock and fishery, I performed two studies. I first addressed the natural mortality rates currently used in the Gulf menhaden stock assessment. To update these rates, I used data from a tagging study conducted from 1970 to 1988. Adult and juvenile menhaden were tagged, released, and recovered in fish processing plants. To evaluate the data, I built a Bayesian model using the negative binomial distribution to estimate natural mortality, catchability, and the overdispersion factor parameters. I established a Base model and n = 17 sensitivity models for robustness. I estimated a constant instantaneous natural mortality of 1.08 y-1 with 95% confidence intervals of 1.04 y-1 to 1.13 y-1. This estimate falls within the stock assessment confidence intervals, and validates the estimation of Ahrenholz (1981). These updated natural mortality rates can be directly used in the stock assessment. I then addressed the need for an implemented fishery reference point. For the fishery to provide verification of sustainability on an annual basis, the Gulf State Marine Fisheries Commission developed an index-based reference point through an algorithm adopted by managers and stakeholders. I developed a web-based application and 3 time series for the use and implementation of the fishery reference point. This dashboard uses processed fishery independent survey data and creates interactive elements for stakeholders to identify the risks of different threshold index values to be used for management.

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