The Role of Sea Turtle Tracking in Conservation
Knowledge gained from satellite telemetry tagging is helping people respond to critical problems facing endangered marine turtles, while contributing to eco-system and community based conservation. Many scientists agree that the best way to restore sea turtle populations to sustainable levels is to protect functionally intact ecosystems. Pelagic predators and grazers, marine turtles have a broad niche that shifts vertically and horizontally with activities such as diving, resting, congregating, traveling and foraging (see Pic. 5). By tracking and following marine turtles we can come to a greater understanding of their place-specific attributes by separating temporally and spatially different populations into “recovery units (7).” Defining these attributes is more easily said than done as, “Some pelagic ecosystems can move kilometers, or even tens of kilometers per day, (for example) particular isotherms, oxyclines, eddies, fronts, upwelling’s at divergence zones, and floating objects aggregated at convergence zones (10).”
Satellite telemetry cannot reveal all of the niche variability particular to marine turtles, but it can be used in unison with other technologies such as satellite imaging, remote sensing buoys, and fisheries logs, in order to develop already existing or new marine protected areas and fisheries closures (10). By taking into account the different life history events of marine turtles, such as feeding, breeding and migration, through the use of telemetry data, we will be able to create effective population level networks of protection. These will allow for greater connectivity throughout marine turtles’ oceanic and terrestrial niche (10). In addition, by defining key habitats for marine turtles, we will be able to determine who is immediately responsible for managing those habitats and for protecting the wildlife that they host. Telemetry is also an effective way to broadcast the importance of marine turtle conservation to students, scientists and the public, thus buffering legal protection with public support.
All seven extant species of marine turtle are highly migratory, and considered oceanic and neritic at different life history stages (Bolten). Their transient behavior causes them to concentrate at certain places and times, spanning whole oceans and occupying various bio-geographical niches and political zones. All marine turtle species are listed as “vulnerable, endangered or critically endangered” on the IUCN Red List, with the exception of the Flatback Turtle, Natator depressus, listed as “data deficient” (11). Their endangered status is a result of marine turtles’ susceptibility to habitat destruction, over-harvesting and indiscriminant fishing practices. A difficulty in researching marine turtles, and the evident lack of data, is due to their often pelagic and submerged state.
Place-specific and increased pelagic protection would mean countering devastating anthropogenic effects by protecting marine turtles in alternate life history phases, and allowing more mothers to reach nesting beaches each season (10). In order to create these paths of protection however, we must first understand where different species of marine turtles are most vulnerable to anthropogenic pressures at sea. Karen Bjorndal, director of the Archie Carr Center for Sea Turtle Research, claims that, “anything that helps us discover geographically where (marine turtles) are, is going to stand us in good stead to be able to protect them.” Currently, satellite telemetry is the most effective way to find marine turtles at sea (4), and potentially our greatest asset in facilitating their conservation (12).
Bjorndal commented on recent stable isotope techniques saying, “now, while I can’t go to a map and point at the spot, at least we know their habitats and diets, and that will guide us where to look.” In contrast, with satellite telemetry that is exactly what we can do, at least with mature turtles that are large enough to physically support the current technology. Moreover, telemetry research is helping us find out why marine turtles are ending up as by-catch, and aiding governments in curbing these proximate causes of mortality.
The Mediterranean long-line fishery is just one of many man-made population sinks, especially for Loggerhead turtle juveniles. This wasteful fishery can be optimally regulated using telemetry data in order to save the Loggerhead, Caretta caretta, from imminent extinction. Lewinson et al. (2004) estimated that in 2000, the worldwide pelagic long line fisheries destroyed around 200,000 Loggerheads and 50,000 Leatherback turtles, with the majority of captures occurring in the Atlantic and Mediterranean (5).” If immediate action is not taken, it is clear that these marine turtle populations will not be able to sustain these high rates of by-catch mortality, and that they will decline inexorably (13). It would be a shame to have to hold domestic fisheries managers and governments accountable for the contemporary extinction of an animal with over one hundred million years of history navigating our planet (14).
Since the first elk was tagged in Wyoming in 1970 (2), satellite telemetry has been used to track the migratory patterns of wild animals throughout their natural habitats (16). Difficulties encountered in using this technology are primarily; “the need to correct for location uncertainty, handle missing or irregular data, and the incorporation of barriers to movement (17).” Loggerhead turtles, for example, don’t surface for long enough intervals, or sufficient times during the typical 7-minute satellite pass, to assure greater location accuracy than 1km. Another possible complication in telemetry research is electromagnetic interference, which is one reason that the telemetry devices are not as small and light as scientists might wish (19), however, the technology improves almost monthly (2). Perhaps its greatest draw back is that satellite telemetry is very costly. One recent study cost US$8,000 for just one year of data.
Nevertheless, it is still a cost effective method when tracking species that migrate across huge spatial scales, and when alternatives require impossible amounts of time, fuel and field resources (20). Furthermore, when plotting a migratory course of 8,000km across the open ocean, missing a few data points, or worrying about physical obstructions, are not major concerns. Close interpretation of the data can also significantly reduce any errors. Moreover, telemetry can be far more accurate than a visual survey from a low-flying aircraft. For instance, when counting Loggerhead turtles, that only spend 50% of their time at the surface, a person in a plane would miss at least 50% of the count (18).
Telemetry research should be carried out with careful planning and precision. Tagging normally begins with the choosing of an individual suited to the particular study. In order to discover where a marine turtle population might overlap with a fishing ground, for example, one might want to tag a female turtle that has completed her nesting cycle. She will then most likely return immediately to the pelagic realm on a quest for food (3). In a different study, one might want to tag a turtle that has been hooked on a long line in order to determine if the induced stress will affect its diving behavior (20).
Once the individual turtle is chosen, a Platform Terminal Transmitter (PTT) is attached to its carapace (21)(see pic. 7,8). The deployment process may take up to two hours and is not beyond the means of a relatively un-experienced group under the supervision of an experienced member. Nor is it overly intrusive on a turtle’s behavior, especially if done while the specimen is in a nesting stupor (16). Once secured, the transmitter will send automatic live updates that can be plotted on maps. These are received every time the turtle surfaces, which triggers a salt-water-sensitive switch that activates the device and allows for prolonged battery life (22). Platform location is determined from the Doppler shift in the frequency received at the satellite, as it moves toward and then away from the PTT, and is communicated to researchers via computer (2). Once activated, the PTT device thus becomes a powerful tool for determining home-range sizes and uses, along with the location of temporary settlements, corridors, migration routes and stop-over sites, all of which are of primary interest for management and conservation (19).
According to Todd Steiner, biologist and executive director of the Turtle Island Restoration Network, “the best way to better manage industrial fisheries to avoid interactions with marine turtles is to understand turtle migrations and reduce fishing effort in migration hot-spots.” Loggerhead turtles are listed as an entire species on the Endangered Species Act of 1978, but this paperwork does not take into account the fact that many unique Loggerhead populations are spread out across the world’s oceans, with each “population unit” subjected to different ecological and anthropomorphic pressures. Moreover, research that unites satellite telemetry tagging and oceanography to reveal abundance and distribution patterns has shown that both Loggerhead turtles and commercial, pelagic fish concentrate in the same highly productive habitats. If you have ever been so fortunate as to witness the diversity of species attracted to a “bait ball” in the open ocean, this comes as no surprise. Unfortunately, aggregated distributions of juvenile loggerhead turtles over-lapping with commercial fisheries in these foraging areas, defined by bathymetric features, fronts, eddies, and geostrophic currents, is increasing the species’ vulnerability to concurrent fishing pressures.
Satellite telemetry has revealed one of these problem areas in Western Mediterranean waters, which provide important feeding grounds for juvenile Loggerheads from two different rookeries, the Mediterranean and the western Atlantic. In this area there are not one, but several human threats to the species, with fisheries and marine pollution being particularly serious (18). Long line fisheries that target swordfish, Xiphias gladius, and blue shark, Prionace glauca, are especially devastating to foraging marine turtles with an appetite for the squid bait (5). The Spanish Mediterranean is a large area where it is predicted that the by-catch associated with long lining for target species, such as sharks, is leading to declining nesting populations of marine turtles in the southeastern United States (5). Due to natural benefits and anthropogenic burdens to marine turtles in this vital geographic area, telemetry will continue to play an important role in making international recommendations for conservation (18).
Perceptively, creating “population recovery units,” and linking nesting populations to neritic and oceanic populations was one of NOAA’s top priorities in their 2008 recovery plan for the Loggerhead turtle. Furthermore, NOAA’s plan called for “empirical substantiation of important population parameters,” which can be done partly through satellite telemetry. It is the ultimate goal of conservationists to use these considerations to accomplish another key element of NOAA’s strategy; to “minimize by-catch in domestic and international commercial and artisanal fisheries (7).”
In tackling the by-catch problem, satellite telemetry is much more effective than opportunistic sampling from incidental captures onboard long lining boats, a method that is largely biased in relation to the specific areas and efforts of the fishing taking place. On the other hand, by using satellite telemetry we can predict the distribution of Loggerhead sea turtles “by monitoring fishing areas in relation to bathymetry and sea surface temperatures.” Ferreira summarizes the needed trade-off between conservation and fishing efforts in a by-catch mitigation policy that:
“(a) Requires vessels to move away from fishing areas after high catch rates of turtles (e.g. sets with 3 or more turtles captures, or 2 or more turtles per 1000 hooks); (b) identifies the key areas and periods of sea turtle aggregation and prohibits long line fishing there (e.g. between July and November inside the Azorean EEZ); or (c) uses dynamic oceanographic monitoring to guide fleet location,” in order to significantly reduce loggerhead by-catch.”
Place-specific management may also be more reliable than gear modification, a common strategy for reducing by-catch, because it is impossible to know if fishermen are actually using legal gear without reports from reliable on-board observers. Furthermore, fishermen tend to associate the use of modified gear with catching certain target species, creating imbalances in fishing efforts that could in turn lead to increased by-catch rates. Ferreira gives a pertinent example in the Azores circle,
“Where hooks might increase the fishing effort towards the unregulated blue shark fishery, because fishermen believe that circle hooks are more effective for sharks than for sword- fish, which would likely lead to an increase in loggerhead fishing interactions during the months of high turtle abundance (5).”
On the other hand, a temporary closure would remind fishermen that the sea must be shared, and that sea turtle conservation is an international priority and not just an afterthought. Indeed, getting the message of conservation through to those on the frontlines is one of satellite telemetry’s greatest strengths as a research tool. This was demonstrated in Aboriginal-owned waters during a 1998-1999 study in Northern Australia.
This study is of particular interest, because it involves an indigenous community of low socio-economic standing using high-tech equipment that was contributed by supporting government and non-government organizations. Furthermore, by temporarily enabling a sustainable harvest it addresses a
“unique human and animal agenda, that requires the opening of communication channels between the fields of conservation, economics, anthropology, and development, where the quintessential solution lies with the local people (9).”
The Yolngu people of North-East Arnhem Land in the Northern Territory “maintain traditional rights and responsibilities for marine turtle management across much of the northern Australian coast”. However, genetic studies and other tagging programs have revealed that marine turtle populations migrate throughout the Indo-Pacific, leading to domestic concerns that diminishing local populations were a result of foreign over-harvesting. The Yolngu, who are traditionally turtle hunters, were quick to notice a deterioration of their resource but did not have the capacity to undertake a decade-long mark and re-capture study in order to investigate their internationally influenced, declining population paradigm.
Four different species, and thousands of individual marine turtles, traditionally use Yolngu waters as rookeries but the Green Turtle, Chelonia mydas, being the most palatable, is number one on the local priority list. To address political and ecological concerns surrounding their historical resources, in collaboration with academics and government researchers, the Yolngu chose satellite telemetry as the best method for tracking twenty female Green Turtles over a ten-month period. By tagging at a local nesting beach towards the end of the nesting season, it was the team’s hope that the mothers would depart for foraging grounds as soon as possible, saving costly time and reducing the risk of copulating males knocking off the expensive tags.
Predictions based on previous telemetry studies were that the turtle mothers would take direct, but disparate routes, North and West, traveling up to 2,600km to foraging grounds in places as far as Western Australia and Papua New Guinea. They were surprised to see that the vast majority, after taking their time nesting one to three more times, followed an almost unanimously southerly course further down into the bay of Carpentaria, where rich eel-grass beds awaited them. The same results over two years, one with much more abundant nesting events than the other, backed the conclusion that this group indeed shared a “home foraging ground.” Significantly, previous studies have shown that Green Turtles maintain foraging grounds for many generations, so long as the food source remains.
Given the international importance of these rookeries and foraging grounds, that may host thousands of endangered Green Turtles, this new information fixed a huge amount of responsibility to the local communities. Although other telemetry and genetic studies have proved the likelihood of individuals from this same population migrating to other countries, and having already been affected by foreigners, this study’s results were nonetheless encouraging. The indigenous groups, who own around 85% of the Northern Coast, became the sole inheritors of a potentially unique genetic population, and in knowing this, took the first step towards managing their faltering resource. These groups are comprised of several hundred people, speaking four different indigenous languages and separated into small outstations. Needless to say, traditional ecological knowledge (TEK) and reverence for the totemic Miyapunu, or marine turtles, will play an important role in their conservation.
Kennett, in order to prevent the “tragedy of the commons” effect, proposed formalizing a network of locals that will make joint decisions to limit the local harvest, keep beaches clean, and continue cooperative scientific monitoring (3). Moreover, collaboration between tourists, who come for the fishing (24), academics, and the government, will allow these communities to use traditional and new knowledge, as well as contemporary technology to manage the local fauna.
The elucidating nature of telemetry is not limited to remote places and inexperienced studies. Data provided by telemetry is commonly expansive compared to that collected by other field methods, such as “very-high-frequency radio tracking (2),” and is also clearly observable for the public and decision makers alike. Several websites, such as {seaturtle.org} even allow us to freely observe marine turtle movements in real time, bringing current telemetry science into our homes, schools and workplaces (see ref. 1 & 25). The “Great Turtle Race,” for example, was a telemetry-based contest sponsored by Conservation International, airing on the popular American comedy-news show “The Colbert Report.” It had thousands of viewers and online browsers tuned in to satellite-tagged leatherbacks migrating 8,000km across the Pacific, adding a human element to the hard science. These are just a few examples of how satellite telemetry can create partnerships between NGO’s, academics, businesses and the media. The benefits of these collaborations will no doubt be reaped in the form of increased nesting beach protection and in the enabling of “dynamic-area closures,” where fisheries are restricted in certain times and places to prevent high incidents of by-catch in the near future.
