Conservation Research on Spotted Eagle Rays in Florida and The

CONSERVATION RESEARCH ON SPOTTED EAGLE RAYS IN FLORIDA AND THE CARIBBEAN SEA Project Technical Report Submitted to the National Aquarium Conservation Center 26 January 2012 Kim Bassos-Hull Center for Marine Mammal and Sea Turtle Research Mote Marine Laboratory Sarasota, Florida Peter Hull, Dean Dougherty, and Krystan Wilkinson Division of Marine Operations Mote Marine Laboratory Sarasota, Florida Robert Hueter, John Morris and John Tyminski Center for Shark Research Mote Marine Laboratory Sarasota, Florida MOTE MARINE LABORATORY TECHNICAL REPORT NO. 1595 1 CONSERVATION SIGNIFICANCE The ultimate goal of the Spotted Eagle Ray Conservation Program is to establish a conservation plan for spotted eagle rays (Aetobatus narinari) in the Gulf of Mexico and Caribbean Sea through collaborative research and multinational relationships. The Spotted Eagle Ray Conservation Program was initiated in 2009 through a conservation partnership between Mote Marine Laboratory and the National Aquarium Conservation Center. This program provides an excellent opportunity to document long-term trends of a near-threatened elasmobranch species as well as provide training opportunities for researchers from other countries to learn sampling techniques and educational outreach possibilities. By engaging Mexican and Cuban research colleagues we hope to address questions of connectivity of spotted eagle ray populations throughout the Gulf of Mexico and Caribbean Sea, and do conservation capacity training and building in those other countries. Our future goals are to monitor fisheries, conduct live-sampling and tagging of individual rays in Mexico, Cuba, and other Gulf of Mexico and Caribbean countries, and further educational outreach by building on our initial years of research along the west coast of Florida. If results of the biological and fisheries research warrant full protection for spotted eagle rays in the Gulf of Mexico, we aspire to be the driving force to make that happen. If not, we will work to ensure that current harvest levels in the Gulf are sustainable. We hope our project will serve as a model for multinational collaboration in conservation of migratory elasmobranch species; including sharks, skates and other rays. PROJECT OVERVIEW In 2009, Mote Marine Laboratory initiated a new conservation research program in collaboration with the National Aquarium Conservation Center on the life history, reproduction, population status, and captive husbandry of the elasmobranch Aetobatus narinari (Euphrasen, 1790), commonly known as the spotted eagle ray. This beautiful large ray is a prized public aquarium animal and is a protected species in Florida state waters. The spotted eagle ray has a worldwide distribution in tropical and warm temperate regions of the Atlantic, Pacific and Indian Oceans and is heavily fished in many regions. Recent genetic studies have shown that Aetobatus does not comprise a single species (Richards et al. 2009), leading to the conclusion that additional knowledge regarding the number of species, their exact distributions and population sizes is imperative for guiding conservation and management efforts. 2 Eagle rays have been targeted in some harpoon fisheries, are sometimes caught as directed catch or bycatch in net fisheries, and have been used as bait in shark fisheries and as meat for human consumption (Cuevas-Zimbrón et al. 2011). Eagle rays are a specialty fishery in Mexico where annual harvest on the Gulf of Mexico coast is estimated to be 200 metric tons (J.C. Perez Jimenez, ECOSUR, Campeche, Mexico, pers. comm.). This would equal approximately 7,350 individuals (avg. wt. est. at 27kg). The sustainability of this fishery is unknown. Growth rates and age to first reproduction are poorly defined for this species as is the reproductive rate. Although eagle rays are fully protected in Florida state waters, it has no protection in U.S. federal waters and is listed as Near Threatened, with a decreasing population trend, in the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species (Kyne et al. 2006, IUCN 2011). For many elasmobranch species, there is growing concern regarding harvest sustainability and the need for conservation of at-risk species. However, the conservation status of most elasmobranchs is classified as data-deficient (IUCN 2010), which underscores the need for basic biological and ecological studies necessary for rational conservation decisions. For example, accurate or even any dietary data, needed to assess the role of large elasmobranch predators in marine communities, are still lacking for the majority of elasmobranch species (Braccini 2008; Heithaus et al. 2008). Ecological data for the spotted eagle ray are sparse but the species likely plays a key habitat-structuring role in seagrass beds and soft benthos as a result of their feeding activity on macroinfauna and macroepifauna. They are large, mobile marine predators that hunt within multiple types of benthic habitats primarily targeting organisms such as clams, scallops, oysters, shrimp, possibly crabs and other mobile epifauna, which the rays crush with their broad, flat teeth (Silliman and Gruber 1999). The rays’ only predators are primarily large coastal sharks, and humans. In some parts of the world, where their shark predators have been severely depleted and the marine ecosystem has been disrupted, large swimming rays such as the spotted eagle ray have been implicated in the decline of shellfish beds. Such cascading ecological effects of worldwide shark depletion are a major theme of much of Mote’s contemporary shark research. Mote researchers have hypothesized that shallow sandbar and seagrass areas in the vicinity of passes may serve as refuges for eagle rays from large sharks, particularly during periods of mating activity or pupping (release of live offspring). Whether they are refuges or not, passes and sandbars appear to be very important areas for spotted eagle ray distribution, meaning that anthropogenic activities that disrupt these areas – specifically, pass dredging and beach renourishment – may constitute threats to the survival of this species in southwest Florida. Mote’s Center for Shark Research (CSR) and Marine Operations Division conducted monthly aerial surveys and weekly on-water surveys from July 2009 through January 2012, establishing that spotted eagle rays are present in most months of the year in southwest Florida coastal waters. Through January 10, 2012, a total of 319 spotted eagle rays were captured, measured, photo-identified and tagged with passive integrative transponder (PIT) tags in the Sarasota area. Four spotted eagle rays were 3 satellite-tagged with Pop-up Archival Tags (PATs; X-Tag, Microwave Telemetry) to track movements for as long as nine months. Individual rays ranging from newborn size of 42 cm disc width to fully mature animals over 2 m disk width were documented in the area. Aerial surveys observed clusters of the rays from St. Petersburg to Sanibel Island, especially around passes. These observations indicate that this ray is concentrated in southwest Florida waters of the Gulf of Mexico, yet critical habitats for feeding, mating and pupping of this species have not been defined. In January-February 2010, unusually cold conditions resulted in a mortality event in the vicinity of a Tampa Bay power plant, which serves as a thermal refuge for a number of marine species including elasmobranchs. More than a dozen spotted eagle rays were found dead and emaciated with poor body condition. Four live rays were caught in a similar emaciated condition. Necropsies of dead specimens showed no food in the animals’ stomachs. During the spring of 2010, when the rays were migrating back into the Sarasota Bay area, several of the rays that were caught near Sarasota Bay passes were visibly thin and underweight. Over the summer of 2010, most of the observed rays appeared to be in normal or robust body condition, suggesting the importance of Sarasota Bay feeding grounds for this species. SUMMARY OF ACTIVITIES & RESULTS Project activities were conducted to address the following long-term research questions: • What is the relative abundance, monthly prevalence, and yearly trends of spotted eagle rays along the southwest Florida coast? • What are the local and long-distance movement patterns of these rays in the eastern Gulf of Mexico? • Where do the rays go in winter, and do they return to the same Gulf coast areas? • What is the reproductive cycle of the spotted eagle ray? • Are spotted eagle rays mating and/or pupping in southwest Florida coastal waters? • How do human-related activities such as beach re-nourishment and channel dredging affect critical habitats for the spotted eagle ray? 4 AERIAL SURVEYS OF THE SOUTHWEST FLORIDA COAST For the past four years, the Mote CSR has conducted aerial surveys to document large coastal sharks along the southwest coast of Florida from Tampa Bay to Sanibel Island (Fig. 1). Typical surveys are conducted once per month when possible during clear weather conditions and take approximately three hours to complete. These surveys are designed to document the location and habitats of large marine vertebrates including marine mammals, sea turtles, teleost fishes, and sharks and rays. Over the past four years (2008-2011), 28 flights have been conducted and a total of 22,150 cownose rays, 2,728 tarpon, 1,067 dolphins, 973 spotted eagle rays, 888 sharks, and 558 manatees have been recorded. Spotted eagle rays are commonly observed on these surveys in the months of May through November (Fig. 2). Figure 1. Aerial survey ST. PETERSBURG flight path (red line). Total survey area covers ~120 nm from John’s Pass near St. Petersburg to Sanibel Island near Ft. Myers. In February and March of 2010 and 2011, the survey included coverage of the Big Bend Power Plant in Tampa to document the presence of spotted eagle rays in the plant’s warm water discharge in winter. FT. MYERS 5 Observed SER over 4 years of Aerial Surveys 180 160 140 120 100 2008 2009 80 2010 60 2011 # SER Observed 40 20 * * 0 NF -20 Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Figure 2.

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