Lukas Heath

Date of Award

2018

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Gardiner, Jayne

Area of Concentration

Marine Biology

Abstract

Nursery areas provide juvenile sharks with abundant prey and protection from predators. Defining these Essential Fish Habitats is an integral component of effective species management and conservation plans. The blacktip shark (Carcharhinus limbatus) is a species of major economic importance in the Gulf of Mexico. The Gulf coast represents nearly continuous habitat for this species, but parturition is thought to occur in discrete nursery areas. Sarasota Bay, on the Gulf coast of Florida, is a 56-mile-long urbanized coastal lagoon system, comprised of five embayments, joined by the Intracoastal Waterway and separated from the Gulf of Mexico by a complex of barrier islands. Once heavily polluted, Sarasota Bay was named an Estuary of National Significance in 1989 and both water quality and seagrass coverage have increased dramatically since that time. Several species of teleost fishes are abundant, including juveniles of economically important species, but elasmobranch populations were not studied until 2016. A seasonal (May through October) monthly gillnet survey of the largest embayment, Sarasota Bay proper, was conducted in 2017 to assess the distribution and relative abundance of elasmobranch species in this estuary. Young-of-the-year (YOY) and juvenile blacktip sharks were encountered in northeastern Sarasota Bay in 2016 and 2017 and relative abundance was comparable to that in Terra Ceia Bay, a wellknown nursery area for this species. Coded acoustic tags were surgically implanted into YOY blacktip sharks to assess residency time and site fidelity to this portion of the bay. Acoustic telemetry revealed frequent use of the area throughout the summer and early fall months. Further, a tagged animal was detected leaving Sarasota Bay just prior to the landfall of Hurricane Irma and returning to the hypothesized nursery area immediately after the storm had passed. Periodic residency in this area continued through late fall, when the animal emigrated from Sarasota Bay as water temperatures began to drop. These results align with the Heupel et al. (2007) criteria for shark nursery areas. Blacktip sharks were also tagged in adjacent Terra Ceia Bay and there were no movements of animals between these two areas, supporting the definition of Sarasota Bay as a separate and distinct nursery area for blacktip sharks.

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