Dr. Brad Wetherbee – Department of Biological Sciences, University of Rhode Island
Dr. Mahmood Shivji – Guy Harvey Research Institute, Oceanographic Center, Nova Southeastern University
Dr. Ben Victor – Ocean Science Foundation
Dr. Richard Nemeth- Center for Marine and Environmental Studies, University of the Virgin Islands

Populations of several species of groupers found off Florida and throughout the Caribbean have declined drastically over the past few decades to the point where groupers are among the species of reef fish for which there is the most concern by agencies tasked with management of coral reef resources. These population declines have led to enactment of restrictions on targeted fisheries, establishment of marine protected areas at spawning sites and other locations, and even listing by NMFS as species of concern with consideration for possible listing as threatened or endangered species under the ESA. These measures are intended to reduce fishing pressure on groupers and enhance recovery of their stocks. Management priorities include identification of essential fish habitat including grouper spawning sites. Although much emphasis has been placed on ecosystem-based management of marine resources, one aspect of the ecology of groupers on their spawning sites that has received little if any attention is their interaction with predators. Anecdotal reports of increased shark abundance at grouper spawning sites during spawning activity, coupled with ecological tenets concerning the ability of predators to limit population growth of prey, suggest that shark predation on groupers at their spawning sites represents a constraint on population growth, and in this case a limit to the rate of recovery of grouper stocks. Despite the logic of such assumptions, other instances of a perceived increase in predator abundance have actually been tied to the presence of

more human observers studying the prey species at a particular time rather than an influx of predators from any considerable distance. This project is aimed at identifying the species of sharks associated with grouper spawning sites off St. Thomas, USVI. The Red Hind Bank Marine Conservation District and a similar refuge at the nearby Grammanic Bank contain spawning sites used by red hind, Nassau grouper, tiger grouper and yellowfin grouper. Fishers and researchers have noted an increase in the abundance of a number of species of sharks at these locations during peak spawning season. The assemblage of sharks observed at these sites includes a variety of species that vary in size, reported feeding habits and documented movement patterns (nurse, Caribbean reef, lemon, bull, great hammerhead and tiger sharks). This project will survey the sharks that occur at these spawning aggregations to document the relative abundance of shark species at the sites and will utilize acoustic transmitters and an array of automated receivers to passively monitor site fidelity, residence and movement patterns characteristic for the major species of shark that are present. The use of depth sensitive transmitters for both sharks and groupers will enable investigation of vertical movements of sharks in the water column in relation to similar movements of grouper during well-synchronized temporal spawning events. Receivers placed within the refuge and at adjacent sites will address the question of whether there is actually an observable increase in shark activity at the sites during the spawning aggregations, whether sharks present are local sharks that are constantly present or that move a short distance to the sites, or whether sharks are moving into the area from greater distances. Such information will ultimately enable assessment of the potential scale of shark predation on groupers at spawning aggregations. Our study will also provide baseline data for tracking changes in shark abundance as grouper populations increase and for comparison among spawning aggregations throughout the Caribbean.

We have recently begun deploying pop-up satellite transmitters on tiger sharks at the spawning site. Click the picture below for a short video of a tiger shark carrying a Microwave Telemetry Inc. satellite transmitter.