ORCID ID

https://orcid.org/0009-0004-0329-6377

Date Awarded

2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

Mary C Fabrizio

Committee Member

Jeffrey D Shields

Committee Member

Rochelle D Seitz

Committee Member

Matthew B Ogburn

Abstract

Commercial fisheries rely on resource managers to develop and enact fishing regulations that prevent stocks from collapsing. In Chesapeake Bay, the goal for blue crab management is to protect the spawning stock to encourage high levels of egg production and thus juvenile recruitment. Management actions to increase female abundance were implemented in the early 2000s, culminating in 2008, in response to an 84% decline in blue crab spawning stock biomass from 1992 to 2000. Blue crabs are the most valuable fishery in Chesapeake Bay and their decline necessitated severe management actions: the historic spawning sanctuary was expanded, the commercial winter dredge fishery was closed, and the exploitation of female crabs was reduced. The status of this fishery is assessed annually using wintertime spawning stock abundance; however, little research has been done to evaluate the reproductive potential or dynamics of females, especially since 2008. Moreover, blue crab reproductive potential is subject to change with shifts in water temperature, exploitation, and individual characteristics. The primary goal of this dissertation was to holistically evaluate blue crab reproductive ecology in Chesapeake Bay over four decades of environmental and management changes, using a combination of novel biomarkers, fishery-independent data from long-term surveys, field sampling, and lab processing. Each chapter is a separate research question; however, all chapters have interrelated conclusions on the reproductive ecology of blue crabs and inform the female-centric management framework in Chesapeake Bay. Chapter 1 compares the proportion of second-year spawners among years with varying exploitation rates in the spawning grounds during winter, prior to the start of the next spawning season. The chapter also includes models of the probability an individual is a second-year spawner based on individual characteristics. Chapter 2 determines if the observed and potential blue crab spawning season are expanding in association with climate change. Chapter 3 estimates batch fecundity relative to historic estimates, as well as individual size, spawning history, and time of year. Chapter 3 also quantifies and models individual quantities of stored sperm, and is the first study to estimate blue crab brood production using paired fecundity and stored sperm quantity data. Last, Chapter 4 assesses the relative abundance of mature females during spawning and evaluates trends in mean size at maturity over time. Chapter four also explores the impact of changes in abundance and size on total egg production using size-specific fecundity. The results of this research indicate that primiparous blue crabs have a high capacity for reproduction, and females in spring, who are more likely to be primiparous, are becoming more vulnerable to fishing mortality with climate change. Since management actions were implemented, exploitation has been reduced and the proportion of second-year spawners, relative abundance, mean size at maturity, and total egg production of the population have improved; however, improvements are marginal or remain below pre-decline levels (i.e., prior to 1992). Moreover, dramatic variability in these metrics highlights the need for more precautionary fishery management. Specifically, the results suggest that conservation of female blue crabs may be improved if the spawning sanctuary is closed to commercial fishing earlier in the year, in accordance with warming, and female exploitation is reduced in spring.

DOI

https://dx.doi.org/10.25773/v5-e8qv-0a77

Rights

© The Author

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