By Neil Hammerschlag
Understanding and predicting animal movement is important as it is central to establishing effective management and conservation strategies [1\. Until relatively recently, studying the movements and behaviors of highly migratory marine species (turtles, sharks, whales, penguins, seals and billfish) have been challenging due to the logistical and technological constraints of working in aquatic environments. However, rapid advancements in electronic tagging and tracking tools have significantly improved the ability of scientists to remotely study the movements of these enigmatic, and often threatened, animals [2,3\.
Recently, Dan Costa and colleagues [4\ summarized new insights in the migrations of large pelagic marine animals arising through the use of electronic tagging (acoustic and satellite telemetry). The paper reviewed how electronic tagging has significantly increased our understanding of their movements over scales ranging from < 10 m to > 5000 km (e.g. turtles, albatrosses, tunas, sharks, and over long time periods (years). Further, Costa and colleagues [4\ reviewed how tagging studies are permitting scientists to understand how movements and habitat use are influenced by environmental (e.g. temperature, chlorophyll) and biological variables (e.g. prey availability) [5,6\. The paper also discussed how electronic tagging been used to establish and evaluate effective conservation strategies for highly migratory marine species; for example, identifying critical habitats of sea turtles for implementing marine protected areas [7\.
Despite these advances and benefits of tagging research, there still remains some areas for improvement. Costa and team suggest that technological research priorities should include improved tag powering mechanisms, increased sensor capabilities, better attachment techniques, tag miniaturization and more efficient data recovery methods.
Emerging analytical tools and technologies capable of measuring the physiological state, movement capacity, and performance ability of marine animals, as well as the environmental factors they encounter, are allowing researchers to increasingly understand and predict why animals move [4, 11-14\ (Figure below). As this field continues to advance, electronic tagging will enable scientists to address some of the most pressing environmental issues of the 21st century, including: (1) how will marine species be impacted by human-induced global change (e.g. warming climate, habitat loss)? (2) What is the adaptive capacity of these species to cope with a changing planet? (3) What will be the associated ecological and evolutionary consequences? (4) if and what strategies can be taken to reduce potential changes and foster conservation of marine species. As tracking tools continue to evolve with advances in technology and research, so will its application for understanding, predicting and responding to the ecological, evolutionary and conservation implications of marine animal movement.
Our Tagging Research
My laboratory at the University of Miami is currently using satellite tags to track the movements of shark species in the subtropical Atlantic Ocean. The goal of this work is to understand the migratory routes and residency patterns of these sharks to identify “hot spots” in place and time that are critical for mating, giving birth and feeding as well as locations where these animals are vulnerable to destructive fishing. By characterizing and identifying these hot spots, we can help supply policy makers with the data they need to implement effective management strategies that will improve conservation for these species. For example, our research has revealed that a great hammerhead tagged in the Florida Keys migrated up the east coast of the United States, as far north as New Jersey before moving offshore. This represented a range extension for this species as they had never been documented as far north. Another of our tagging research focusing on tiger sharks that are fed at a popular ecotourism dive site in the Bahamas, found that the dive tourism did not impact the long-term, large-scale movements of the tiger sharks (Check out a video summary here). Moreover, the tiger sharks tracked made extensive migrations thousands of kms out in the middle of the Atlantic Ocean on foraging forays (see map below). Our tracking of bull sharks and tarpon in the Florida Keys revealed that both the sharks and tarpon swam through similar areas, but that tarpon altered their movements in areas frequented by bull sharks to avoid chances of being attacked. In fact, tarpon appeared to even forfeit the best feeding sites to minimize their risk of predation from bull sharks. You can track the movements of our tagged sharks through an interactive google earth map on our website. More....