Year of Publication

2014

Season of Publication

Fall

Paper Type

Master's Thesis

College

College of Arts and Sciences

Degree Name

Master of Science in Biology (MS)

Department

Biology

NACO controlled Corporate Body

University of North Florida. Department of Biology

First Advisor

Dr. Jim Gelsleichter

Second Advisor

Dr. Carolyn Belcher

Third Advisor

Dr. Eric Johnson

Department Chair

Dr. Daniel Moon

College Dean

Dr. Barbara Hetrick

Abstract

Understanding the life history of marine wildlife is essential for the management of both commercial and recreational fisheries. Bonnetheads (Sphyrna tiburo) are a component of the small coastal shark (SCS) fishery complex, and are caught regularly in both types of fisheries. Despite being well studied in the Gulf of Mexico, little is known about bonnetheads from the U.S. Atlantic coast. The goal of the first component of this study was to provide new, key information on their life history to improve management of U.S. Atlantic populations, particularly by identifying reproductive seasonality, periodicity and fecundity. This was accomplished by examining sexually mature male and female bonnetheads, collected monthly (2012-2014) from South Carolina, Georgia, and Florida waters, and monitoring changes in reproductive tract morphology. Changes reflected a seasonal reproductive cycle with an annual breeding periodicity. Histology was used to confirm events and identify other important periods in the reproductive cycle, such as sperm storage in females. Overall, Atlantic coast bonnetheads were found to exhibit reproductive patterns similar to those reported in the Gulf with slight temporal shifts in the time of mating and ovulation and slightly lower fecundity ranging between 1 and 12 with an average (±SE) of 7±3.8. Additionally, the second component of this study aimed to understand gonadal sex hormone regulation in S. tiburo reproduction with a particular focus on female sperm storage. Circulating plasma sex hormones increased in association with specific reproductive events. Plasma 17β-estradiol and testosterone concentrations increased during sperm storage, whereas progesterone levels increased near the end of this stage. Immunocytochemical analysis of androgen, estrogen, and progesterone receptors in the oviducal viii gland, the organ that stores sperm in female bonnetheads, demonstrated that epithelial cells of sperm storage tubules and spermatozoa itself are direct targets for these hormones, playing a role in regulating this poorly understood process.

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