Telemetric and Genetic Analyses of Habitat Use, Philopatry and Natal Homing of a Coastal Shark Species in Continental Nursery Areas

Mote Marine Laboratory, Sarasota FL

Investigators

Abstract

The ocean's migratory vertebrates, including marine fishes, sea turtles, sea birds and marine mammals, are tied to the sea's margins in ways that are not completely understood. These marine animals often depend on inshore regions for reproduction, feeding and other essential activities during critical stages of their life histories. What delineates one coastal area from another as preferred habitat for these migratory species is poorly known, particularly for broad continental regions where suitable habitat appears to be widespread. How and why a species selects a specific continental coastal area for reproduction and early life stages -and whether the same geographic site is utilized by individual animals in an evolutionarily fixed way- remain somewhat of a mystery, particularly in the case of sharks, the predominant apex predators in the sea. Previous research on shark nursery areas conducted by Mote Marine Laboratory since 1991 has shown that at least 14 coastal shark species utilize inshore regions of the Gulf of Mexico coast of Florida as pupping and/or nursery areas. This research has shown that neonate blacktip sharks (Carcharhinus limbatus) are abundant in coastal bays and estuaries of the Florida Gulf coast from May through September before migrating south for the winter. This project will examine the use of a bay as a nursery area for neonate and juvenile C limbatus, attempt to define the ecological role of this area in the life history of young sharks and if use of these areas has resulted in evolution of philopatry. The research objectives are to: 1) delineate the activity patterns, home range and habitat preferences of young C limbatus in a nursery area and ascertain how long these animals reside within a specific continental nursery area; 2) estimate the return rate (philopatry) of one year-old animals to the natal nursery and defiiie their continued use of the nursery area; and 3) determine if adult female sharks return fo their natal nursery area to give birth (natal homing) through analysis of genetic variation within the population. This research will be conducted in Terra Ceia Bay, a continental nursery area along the central Gulf coast of Florida. A state-of-the-art system of remote acoustic hydrophones will be deployed within the nursery area during spring, summer and fall months to continuously monitor the location and movement of sharks fitted with ultrasonic transmitters. Data collected from hydrophone stations will be used to determine the residence time, activity patterns, home range and habitat use of young sharks in the nursery area. Once the use of Terra Ceia Bay as a nursery area for neonate C. limbatus has been defined it will be important to examine whether specific nursery areas continue to be integral in the life history of juvenile sharks. The return rate of young sharks to their natal nursery will be examined using the hydrophone system and by conducting sampling in three adjacent coastal nursery areas (Pine Island Sound, Yankeetown, Ten Thousand Islands). Continued monitoring of Terra Ceia Bay will provide information on residence time, activity patterns, home range and habitat use for the same individuals as non-neonate juveniles. Use of the remote acoustic system will provide the primary data to accomplish the first two objectives of this study. Genetic analyses will test for the occurrence of philopatry to support hydrophone results and test for natal homing by adult females. These analyses will provide the data necessary to evaluate the hypothesis of natal homing by female sharks. Although philopatry and natal homing are widely known in other animal species, this study will provide the first directed effort to elucidate these behaviors within an elasmobranch population, particularly one inhabiting a continental region where suitable nursery habitat is widespread and not insular. Results of this study will present continuous data concerning the habits of young sharks without disturbance by scientists during tracking. Overall, this project will examine the larger role of the coastal nursery area in the life history of shark species inhabiting continental shelf waters.