Year

2018

Season

Summer

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. Eric Johnson

Rights Statement

http://rightsstatements.org/vocab/InC/1.0/

Third Advisor

Dr. James Sulikowski

Department Chair

Dr. Cliff Ross

College Dean

Dr. George Rainbolt

Abstract

Although tiger sharks are an important apex predator in many ecosystems, little is known about their reproduction. The goal of this study was to determine the size-at-maturity and the reproductive seasonality of tiger sharks in the western Atlantic Ocean. This was achieved using a combination of ultrasonography and measurements of plasma hormone concentrations; in particular, testosterone for males and estradiol and progesterone for females. Steroid hormone concentrations were measured using chemiluminescent assays (CLIA). Maturity was also examined through histology of reproductive organs in females and clasper calcification in males. Females were found to mature between 270 and 310 cm total length and males were found to mature between 260 and 300 cm total length. Mating was determined to occur in October/November, based on the presence of mating wounds on females and increased concentrations of testosterone in males. Some females were shown to exhibit increased plasma estradiol concentrations also during October/November; however, we do not believe that ovulation takes place until May or June based on ultrasonography data. This suggests a period of sperm storage although histological examination of the oviducal gland was not able to confirm this. Ultrasonography data, showing increasing embryo size over the course of a year, and data on minimum size of tiger sharks caught in longline surveys suggested that parturition occurs between June and September with pups being born as small as 56 cm fork length. The findings from this study show that some tiger sharks reach reproductive maturity at sizes smaller than what has been previously suggested. Additionally, the possibility of tiger sharks storing sperm suggests that their reproductive cycle is a minimum of two years long and could be up to three years in duration. This information is important for management of the species in the future. Additionally, this study adds to the limited knowledge about reproduction of elasmobranchs and how patterns of reproductive steroids can correlate with different reproductive events.

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