Date of Award

Spring 3-26-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Ocean Science and Engineering

Committee Chair

M. Zachary Darnell

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Robert Griffitt

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Frank Hernandez

Committee Member 3 School

Ocean Science and Engineering

Committee Member 4

Marcus Drymon

Abstract

Effective management of commercial fisheries is a challenge as it must balance social, economic, and biologic costs for the betterment of the population in the long term, while also sustaining the fishermen who rely on the industry in the short term. The first step in establishing an effective balanced management plan is to understand the biology and habitat use of the exploited stock. Blue crabs are one of the most commercially and ecologically significant species in the United States. Coast-wide U.S. commercial landings in 2019 totaled 147 million pounds for a dockside value of $206 million. Blue crabs also play a major role in structuring faunal communities and serve as predators and prey throughout estuarine landscapes. Blue crab landings and estimates of abundance fluctuate dramatically year-to-year, and many states have seen decreases in landings and abundance in recent years. Louisiana, the nation’s leader in blue crab landings for 18 of the last 20 years, is one of the states that has experienced declines in recent years: the spawning stock biomass in 2015 was the lowest in history, and the fishery was overfished during 1995, 2013, and 2015. Management efforts for the fishery have been hindered by an incomplete knowledge of the migration patterns of Louisiana blue crabs, and the need to understand the life history of this species and the dynamics of natural and fishing mortality has been highlighted by the Louisiana Department of Wildlife and Fisheries in order to ensure continued sustainability of the fishery. The goal of this dissertation was to address these research needs by examining the migratory movements, behavioral mechanisms underlying spawning migration, fishery exploitation, and potential for sperm limitation of the Louisiana blue crab spawning stock. Adult female blue crabs migrate large distances, up to 443 km, though this migratory movement varies spatially and temporally. The underlying mechanism for these movements likely involves exogenous cues, rather than circatidal endogenous cues observed in other areas since tidal cycles are variable and unpredictable. Approximately 47% of the Louisiana blue crab population in the three basins examined are subject to fishing pressure, though this varies spatially and temporally as well. The Louisiana blue crab spawning stock is severely sperm limited. This dissertation provides previously unknown life cycle and fishery data that can be used to develop future management plans to improve conservation efforts and insure the longevity of this economically and ecologically important species.

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