Tarpon Week is off to a great start, and we hope anglers are learning a lot about how to catch and fight tarpon. But it’s time to jump back into some fascinating science and conservation work by Bonefish & Tarpon Trust. Dr. Aaron Adams is BTT’s Director of Science and Conservation. He is a renowned scientist who has added extensively to the state of tarpon, bonefish, and permit science. If we asked Aaron about all his work and what he knows about these flat species, you would quite literally be reading for all of Tarpon Week.
So, for this interview, Aaron focused on the project at hand: BTT’s Tarpon Isotope Study. This effort seeks to better understand where tarpon are going and what they’re eating to inform future conservation and policy recommendations. Follow along for a fascinating discussion!
Flylords: Aaron, before we dive into some fascinating tarpon science, can you share a little background on how you got into the world of fisheries science?
Aaron: I grew up in Maryland and started fishing at the age of 4 or 5. It didn’t take long for the fascination with fishing to evolve into a lot of ‘why’ and ‘how’ questions, so studying fish came naturally. My fishing informs my science, and science informs my fishing. And both feed my focus on conservation. Plus, as I was growing up, the Chesapeake Bay was collapsing—the fisheries for striped bass, blue crabs, and oysters were in trouble due to pollution, habitat loss, and overfishing—essentially, mismanagement of the resources. This combination of my interest in fishing, science, and seeing the Bay collapse was pretty formative in my career path.
Throughout my career, I’ve lived and worked in the mid-Atlantic, southern and central California, the Caribbean Sea, and both coasts of Florida. Everywhere I’ve worked has been somewhere on the slope from being a pristine environment to a degraded environment. So this is a widespread theme. Local knowledge is an important component in the process of determining the status of local environments and fisheries—anglers and guides are on the water a lot and have a lot of useful experience. Therefore, collaborating with the fishing community to gather the necessary knowledge for improved resource management is a common need and a significant motivation for our work.
Another formative moment in my career was when I was in graduate school getting my Ph.D. I was put in charge of organizing a lecture series that featured guests from the general field of marine conservation. All of the speakers were amazing, but each had one regret—they regretted not speaking up about the decline of the ecosystems they had worked on, instead continuing to focus on the science. That removed any inhibitions I still had about applying science to conservation.
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Flylords: You’ve done loads of research and scientific studies on all things bonefish, tarpon, and permit. How has your understanding of these species, and I guess all of ours, expanded over the years?
Aaron: There has been an amazing expansion in our knowledge of these species. When BTT started in the late 1990s, there had been only a handful of studies on bonefish, tarpon, and permit. Although those studies provided a good foundation with essential information, they were basic science—mostly subjects like growth rates and diet. Over the past 20 years or so, dozens of studies have been conducted, resulting in numerous research articles published. So the knowledge increase has been exponential.
All of this information has enabled us to focus on understanding and addressing the major threats to the fisheries and their habitats, both through new research and by applying research findings to policy. This wasn’t possible way back when this all started. Plus, we spend a lot of effort sharing the science results, conservation needs, and other aspects of what we do with the fishing community. The better educated the fishing community, the more likely we are to get better policies and resource management because the fishing community demands it.
Flylords: Ok, the science at hand right now is tracking tarpon and an isotope study. At a high level, can you share some toplines about what you’re doing? And how do these two studies complement each other?
Aaron: The first step was to tag tarpon and track them over multiple years to document and understand their seasonal migration patterns. We used acoustic tags that lasted for 5 years, allowing us to track individuals for multiple years and assess the repeatability of their migration patterns. Do tarpon tend to follow the same migration patterns, or do individuals mix it up from year to year? Overall, there was a lot of repeatability. The tracking study results show that there are three groups, we’ll call them subpopulations, of tarpon. There is a mixing zone in the Florida Keys, where tarpon gather for the spawning season. Then, from this mixing zone, one subpopulation migrates up the Atlantic coast, and another migrates up the Gulf coast. The Mississippi Delta is another mixing zone, where tarpon from the Florida Gulf coast subpopulation mix with tarpon from the western Gulf (Mexico to Texas) subpopulation. This suggests that we need to consider tarpon management at the regional scale, as we are sharing the same fish.
The second step was to determine the types of prey tarpon depend on during their migrations. For example, do they rely on prey from freshwater or saltwater areas? What habitats are most important for tarpon prey? Do tarpon depend on prey from seagrass and marsh habitats, or ocean habitats? Do they change what they eat during their migration? We used Stable Isotopes from tarpon fin tissue to answer these questions.
Flylords: Stable isotope studies were not taught in any of my high school science classes… What does this process look like, and how can you turn around the data to get an idea about what that tarpon was eating?
Aaron: Essentially, you are what you eat. What you eat is reflected in the makeup of your tissue. Specifically, the isotopes (or forms) of Nitrogen, Carbon, and Sulfur are used to determine, for example, whether tarpon are eating prey from a seagrass-based food web or an ocean-based food web, or from a freshwater-influenced environment or the open ocean. This is because the proportions of the different isotopes of Nitrogen, Carbon, and Sulfur differ among these habitats. This doesn’t let us know the specific species of prey tarpon depend on, but does tell us if they are feeding on a type of baitfish that eats plankton in open water (like menhaden) versus crabs and shrimp that live in seagrass beds.
Flylords: Why is it important to know what tarpon are eating?
Aaron: What tarpon eat is reflective of the environments they are in. And the characteristics of the environments influence the prey that is available. For example, tarpon may eat a lot of blue crabs in some areas. These blue crabs depend on seagrass habitats. Knowing that tarpon depend on a seagrass-based food web tells us we need to prioritize seagrass conservation in those regions. And since seagrass health is influenced by changes in freshwater flows (more freshwater means less seagrass), this means that we have to keep an eye on activities that change freshwater flows into coastal areas. The bottom line is that tarpon diet is only as good as the health of the habitats and water they swim and forage in, and the diet information gives us more ammunition for addressing environmental threats, from pollution to overharvest of prey species. In addition, we can get an idea of the foraging hotspots for tarpon, which helps prioritize conservation efforts.
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Flylords: What are you learning through the isotope study?
Aaron: Important foraging areas for tarpon are South Florida, the Mississippi Delta region, and the mid-Atlantic coast. So this prioritizes these regions for conservation.
In the mid-Atlantic and Mississippi Delta region, tarpon heavily depend on ocean forage fish like menhaden, which has applications to the ongoing efforts toward better management of the menhaden fishery. In South Florida, they depend more on prey from seagrass beds, which supports our ongoing focus on habitat health in Florida. Juvenile tarpon have a high reliance on prey associated with freshwater inflows, which speaks to the need for juvenile tarpon habitat protection and restoration.
Flylords: It’s no secret, tarpon and many other fish species are showing up in new areas with some increasing consistency…Chesapeake Bay, for one, is one of those regions…this massive estuary also allows a massive industrial menhaden fishery…things like that have to be a concern, right?
Aaron: I remember seeing some angler accounts from many decades ago of fishing for tarpon on the eastern shore of Chesapeake Bay, so tarpon have long relied on foraging in the Chesapeake Bay region. The same goes for the Mississippi Delta area.
Tarpon don’t make these long-distance seasonal migrations for fun; they do it to access areas where they can put the feedbag on and take on a lot of nutrition. As we alter these areas, whether by overharvesting forage fish that tarpon rely on or polluting habitats so there are fewer prey, tarpon will be impacted.
Flylords: Ok, now putting these findings together, what does the future for tarpon look like? Are there actionable findings from these studies that can improve tarpon conservation now and in the long term?
Aaron: There are numerous actionable findings from these studies.
The migration patterns of adult tarpon underscore the need for regional management. The tarpon that are part of the fishery in the Florida Keys are some of the same tarpon that are fished for in other areas, from Chesapeake Bay to the Mississippi Delta. Some states have better regulations than others, so improving lax regulations is important.
The diet of tarpon depends a lot on the amount of freshwater reaching coastal areas, so one of our next steps will be to estimate how changes in freshwater flows due to upland and coastal development are impacting tarpon prey.
Adding tarpon to the list of economically important fish that rely on menhaden will add more weight to improving menhaden harvest regulations.
Flylords: When can people learn more about these BTT studies and then get involved to promote BTT’s conservation efforts?
Aaron: We recently featured the tarpon studies in the BTT Journal in the Fall 2024 issue. That can be accessed online here.
We will be putting out additional information on the tarpon studies this summer. And the projects will be presented as part of the BTT Symposium in November in Fort Lauderdale–learn more about that here. But we’d encourage everyone interested in learning more to explore our website and support our mission however they can.
Cover picture courtesy of Paul King and BTT.
BTT’s Juvenile Tarpon Habitat Work, Supporting Future Silver Kings
