Megalops Atlanticus Research Articles

The silver king in the Magic City: Observation of Atlantic tarpon Megalops atlanticus aggregation off Miami, Florida.

Due to the logistical and financial challenges in studying migratory marine species, there is relatively limited knowledge of the reproductive biology, behavior, and habitat use of many ecologically important marine megafauna species, including the Atlantic tarpon Megalops atlanticus. Here, we present a novel observation using consumer-grade aerial drones to observe, quantify the scale of, and classify behaviors within a previously unreported tarpon aggregation (N = 182) over the course of a 2-day fish aggregation event. After the event, we analysed and compared observed behaviors (e.g., cruising and clustering) with those of other fish species with well-documented reproductive behaviors, revealing behaviors potentially consistent with courtship, leading us to believe this to be a possible spawning aggregation or aggregation of reproductive/migratory significance. This aggregation occurred in highly altered and urbanized habitat off the coast of South Florida, during the winter, and outside of tarpon's previously reported spring and summer spawning season. Although few studies to date have used drones to monitor teleosts, this study reinforces their potential value as a tool for monitoring fish populations, behavior, and movement.

Characterizing Juvenile Common Snook and Tarpon Habitat to Guide Conservation and Restoration of Coastal Wetlands

To conserve or restore juvenile fish habitat, resource managers, restoration practitioners, and engineers need fine-scale information to understand what conditions they need to preserve or what specifications are needed to create new habitat. The objective of this study was to develop statistical models using a dataset of 18 coastal ponds in Southwest Florida, USA, to predict the abundance of juvenile common snook Centropomus undecimalis (hereafter snook) and presence of juvenile tarpon Megalops atlanticus, both of which are flagship species used for conservation and restoration of subtropical and tropical wetlands. Model predictors included water conditions and characteristics of vegetation, sediment, and geographic position. Modeling results indicated that juvenile snook used coastal ponds that were directly connected to tidal creeks. In contrast, juvenile tarpon were more likely to be present in coastal ponds that were separated from tidal creeks by dense mangrove forest (e.g., elevation > 0.48 m above Mean Low Water) characterized by highly organic sediment and low dissolved oxygen, to which tarpon are well adapted. Overlap between snook abundance and tarpon presence was greatest where connections between ponds and the nearest tidal creek were at a relatively low elevation (e.g., -0.12 m relative to Mean Low Water). Although these findings are most applicable to management and conservation of populations in areas along the Gulf coast of Florida (i.e., in areas of similar tidal range and coastal geomorphology), incorporating more detailed habitat surveys to better capture landscape context, geomorphology, and connectivity into fish sampling designs should be broadly applicable to estuarine fish ecology.

Emigration of Juvenile Tarpon Megalops atlanticus from Ephemerally Connected Coastal Ponds

Worldwide, coastal wetlands are threatened by disrupted hydrology, urbanization, and sea-level rise. In southwest Florida, coastal wetlands include tidal creeks and coastal ponds, which are the primary habitats used by juvenile Tarpon, Megalops atlanticus, an important sport fish. Coastal ponds can occur near uplands and are ephemerally connected to the open estuary, creating conditions of variable dissolved oxygen and salinity. Juveniles can tolerate wide-ranging abiotic conditions, but little is known about how they egress from their remote nursery habitats, which often requires them to cross > 1 km of mangrove forest to reach the open estuary. The objective of this study was to (1) compare Tarpon body condition among ponds close to the open estuary versus those ponds farther away on the Cape Haze peninsula of Charlotte Harbor, Florida, and (2) using acoustic telemetry determine what factors contribute to Tarpon emigration from the ponds to open estuarine waters. We tested the hypothesis that distinct groups of Tarpon occur in isolated ponds, leading to variation in fish length and body condition, and that opportunities for emigration from these ponds hinge on high water events. No pond stood out as having Tarpon of low body condition. Factors contributing to increased probabilities of Tarpon emigration were low barometric pressure, high-water level, and Tarpon body length. Tarpon emigrated from ponds near tidal creeks during summer king tides, while tropical cyclone conditions were needed to allow for movement from ponds farther in the landscape. The juvenile Tarpon were later detected at the mouths of large rivers 30 km up-estuary. The characterizations of water levels and event criteria needed for successful Tarpon nurseries should aid in habitat conservation and the creation of Tarpon nursery habitat in restoration designs.

Diet of age-0 tarpon Megalops atlanticus near their northern range limit in the western Atlantic Ocean

Diet of age-0 tarpon Megalops atlanticus near their northern range limit in the western Atlantic Ocean

Spatial distribution and movement of Atlantic tarpon (Megalops atlanticus) in the northern Gulf of Mexico.

Atlantic tarpon (Megalops atlanticus) are capable of long-distance migrations (hundreds of kilometers) but also exhibit resident behaviors in estuarine and coastal habitats. The aim of this study was to characterize the spatial distribution of juvenile tarpon and identify migration pathways of adult tarpon in the northern Gulf of Mexico. Spatial distribution of juvenile tarpon was investigated using gillnet data collected by Texas Parks and Wildlife Department (TPWD) over the past four decades. Generalized additive models (GAMs) indicated that salinity and water temperature played a significant role in tarpon presence, with tarpon occurrences peaking in the fall and increasing over the past four decades in this region. Adult tarpon caught off Texas (n = 40) and Louisiana (n = 4) were tagged with acoustic transmitters to characterize spatial and temporal trends in their movements and migrations. Of the 44 acoustic transmitters deployed, 18 of the individuals were detected (n = 16 west of the Mississippi River Delta and n = 2 east of the Mississippi River Delta). Tarpon tagged west of the Mississippi River Delta off Texas migrated south in the fall and winter into areas of south Texas and potentially into Mexico, while individuals tagged east of the delta migrated into Florida during the same time period, suggesting the presence of two unique migratory contingents or subpopulations in this region. An improved understanding of the habitat requirements and migratory patterns of tarpon inhabiting the Gulf of Mexico is critically needed by resource managers to assess the vulnerability of each contingent to fishing pressure, and this information will guide multi-state and multi-national conservation efforts to rebuild and sustain tarpon populations.

Depredation rates and spatial overlap between Great Hammerheads and Tarpon in a recreational fishing hot spot

AbstractObjectiveShark depredation, the full or partial consumption of a hooked fish by a shark before it is landed, is an increasing source of human–wildlife conflict in recreational fisheries. Reports of shark depredation in the catch‐and‐release Tarpon (also known as Atlantic Tarpon) Megalops atlanticus fishery in the Florida Keys are increasing, specifically in Bahia Honda, a recreational fishing hot spot and a putative Tarpon prespawning aggregation site.MethodsUsing visual surveys of fishing in Bahia Honda, we quantified depredation rates and drivers of depredation. With acoustic telemetry, we simultaneously tracked 51 Tarpon and 14 Great Hammerheads (also known as Great Hammerhead Sharks) Sphyrna mokarran, the most common shark to depredate Tarpon, to quantify residency and spatial overlap in Bahia Honda.ResultDuring the visual survey, 394 Tarpon were hooked. The combined observed shark depredation and immediate postrelease predation rate was 15.3% for Tarpon that were fought longer than 5 min. Survival analysis and decision trees showed that depredation risk was highest in the first 5–12 min of the fight and on the outgoing current. During the spawning season, Great Hammerheads shifted their space use in Bahia Honda to overlap with Tarpon core use areas. Great Hammerheads restricted their space use on the outgoing current when compared to the incoming current, which could drive increased shark–angler interactions.ConclusionBahia Honda has clear ecological importance for both Tarpon and Great Hammerheads as a prespawning aggregation and feeding ground. The observed depredation mortality and postrelease predation mortality raise conservation concerns for the fishery. Efforts to educate anglers to improve best practices, including reducing fight times and ending a fight prematurely when sharks are present, will be essential to increase Tarpon survival and reduce shark–angler conflict.

Cross-habitat utilization of fish in a tropical deltaic system as a function of climate variability and body size: Are mangroves fish nurseries in a tropical delta?

The temporal variability of fish habitat utilization is poorly understood in tropical deltaic systems due to high water turbidity, which limits visual censuses, and to the lack of long-term data incorporating climate variability events. We aimed to assess the influence of body size and El Niño Southern Oscillation (ENSO) variability on the cross-habitat utilization rate of 14 fish species of commercial relevance in the Ciénaga Grande de Santa Marta (CGSM). We estimated the utilization of mangroves and coastal lagoons based on relative catch frequencies from encircling gillnets used within a long-term catch monitoring program, and then tested for significant changes in each species' habitat utilization as a function of body size and climate variability. Six species showed a high dependence on mangroves and four on coastal lagoons for most body size classes (including juveniles) and ENSO conditions. One species (Elops smithi) showed a high utilization of mangroves in some ENSO phases and body size classes, while three species showed a high utilization of both mangroves and coastal lagoons. Mangrove utilization by six species (Megalops atlanticus, E. smithi, Centropomus undecimalis, Mugil incilis, Mugil liza, and Ariopsis canteri) increased in larger body sizes at low depths, which usually occurs under dry ENSO conditions, when predatory risk is higher in coastal lagoons. Another species (Caquetaia kraussi) increased its mangrove utilization from the body size at which its feeding habits change. Mangroves and coastal lagoons are important nurseries and habitats for adults of the main commercial fish species in the CGSM. Seascape habitats and fringe/riverine mangroves must be conserved in tropical deltas to promote not only nurseries but also fish lifecycles.

Individual variation and repeatability of Atlantic tarpon Megalops atlanticus migrations in the southern US: implications for conservation and management

Individual variation and repeatability of Atlantic tarpon Megalops atlanticus migrations in the southern US: implications for conservation and management

Tropical estuarine ecosystem change under the interacting influences of future climate and ecosystem restoration.

One of the largest restoration programs in the world, the Comprehensive Everglades Restoration Plan (CERP) aims to restore freshwater inputs to Everglades wetlands and the Florida Bay estuary. This study predicted how the Florida Bay ecosystem may respond to hydrological restoration from CERP within the context of contemporary projected impacts of sea-level rise (SLR) and increased future temperatures. A spatial-temporal dynamic model (Ecospace) was used to develop a spatiotemporal food web model incorporating environmental drivers of salinity, salinity variation, temperature, depth, distance to mangrove, and seagrass abundance and was used to predict responses of biomass, fisheries catch, and ecosystem resilience between current and future conditions. Changes in biomass between the current and future scenario suggest a suite of winners and losers, with many estuarine species increasing in both total biomass and spatial distribution. Notable biomass increases were predicted for important forage species, including bay anchovy (+32%), hardhead halfbeak (+19%), and pinfish (+31%), while decreases were predicted in mullet (-88%), clupeids (-55%), hardhead silverside (-15%), mojarras (-117%), and Portunid crabs (-16%). Increases in sportfish biomass included the angler-preferred spotted seatrout (+9%), red drum (+10%), and gray snapper (+8%), while decreases included sheepshead (-40%), Atlantic tarpon (-73%), and common snook (-507%). Ecosystem resilience and fisheries catch of angler-preferred species were predicted to improve in the future scenario in total, although a localized decline in resilience predicted for the Central Region may warrant further attention. Our results suggest the Florida Bay ecosystem is likely to achieve restoration benefits in spite of, and in some cases facilitated by, the projected future impacts from climate change due to the system's shallow depth and detrital dominance. The incorporation of climate impacts into long-term restoration planning using ecosystem modeling in similar systems facing unknown futures of SLR, warming seas, and shifting species distributions is recommended.

Correction: Seasonal variation in the phenology of Atlantic tarpon in the Florida Keys: migration, occupancy, repeatability, and management implications

Correction: Seasonal variation in the phenology of Atlantic tarpon in the Florida Keys: migration, occupancy, repeatability, and management implications

The effects of temperature and salinity on the blood chemistry and survival of juvenile Atlantic tarpon Megalops atlanticus.

Atlantic tarpon Megalops atlanticus are highly migratory sportfish that support recreational fisheries throughout their range. In US waters, juveniles can be found in coastal and estuarine habitats along the Gulf of Mexico and Atlantic seaboard, with temperature limiting their northern latitudinal distribution. Juveniles may overwinter in these areas during the first several years of life. Low temperatures are known to cause mortality in adults, but the challenges of temperature are less understood for juveniles. Furthermore, salinity, which can change dramatically in these habitats, may have a synergistic effect with temperature. To examine the physiological effects of temperature and salinity on juvenile tarpon, wild fish were acclimated to a range of conditions that potentially occur in the northern range of their estuarine habitats. The haematology of juvenile tarpon was examined in two salinity (≤2 and ≥30 ppt) and temperature (15 and 25°C) treatments, followed by a low-temperature tolerance test. After 2 weeks in treatment conditions, blood samples were analysed for haematocrit, pH, red blood cell concentration, haemoglobin content and plasma osmolality. Increased plasma osmolality was observed in fish at low temperature (15°C compared to 25°C) and at high salinity (≥30 ppt compared to ≤2 ppt). Blood pH was increased at 15°C compared to 25°C, with the highest pH at 15°C and low salinity. Haemoglobin, haematocrit and red blood cell concentration were higher at 25°C than 15°C, with haemoglobin lowest at 15°C and low salinity. For the low-temperature tolerance test, all fish were acclimated to 15°C for 2 weeks, then transferred to separate tanks where temperature was gradually decreased at 0.9 ± 0.1°C/h until fish lost equilibrium. Fish at low salinity lost equilibrium more rapidly (1 ppt, 12.65 ± 0.46°C) than fish at high salinity (30 ppt, 11.26 ± 0.14°C). The results indicate juvenile tarpon are susceptible to low temperature, which is exacerbated by low salinity, findings useful in the assessment of juvenile tarpon overwintering habitat.

A participatory climate vulnerability assessment for recreational tidal flats fisheries in Belize and The Bahamas

Recreational fishing is a pillar of the multibillion-dollar tourism sector in the Caribbean, supporting economic development and community livelihoods. However, as climate change drives increased habitat degradation, key recreational target species may experience declines. To effectively prioritize adaptation and mitigation efforts it is critical to project climate change impacts on recreational species and the communities that depend on them. We conducted a comprehensive climate vulnerability assessment (CVA) for three recreationally important tidal flats species in Belize and The Bahamas: bonefish (Albula vulpes), tarpon (Megalops atlanticus), and permit (Trachinotus falcatus). Species vulnerability was assessed by coupling 1) a research-based CVA to evaluate the sensitivity and exposure of species to climate impacts with 2) a participatory workshop involving 17 fishing guides, resource managers, and science and policy experts working in fisheries systems in Belize and/or The Bahamas. The workshop elicited local expert knowledge to resolve and contextualize CVA scoring and to identify strategies to increase climate resilience. According to the research-based CVA, key climate factors in the Caribbean are expected to see a ‘very high’ magnitude of change by 2050. All three species exhibit ‘very high’ vulnerability to these changes based on life history traits and reliance on nearshore habitats that are exposed to rapid temperature increases and storm damage. The expert stakeholder group confirmed a ‘very high’ magnitude of expected climate impacts in the Caribbean region, to which bonefish, the most valuable species, is likely to have a ‘very high’ vulnerability. However, stakeholders perceived tarpon and permit to be less vulnerable to these impacts than the CVA predicted, based on “on the water” observations of their habitat flexibility and resilience to disturbance. The group identified strategies at the individual, community, national, and international levels to enhance climate resilience in the recreational fishing sector. Our work highlights how participatory CVA processes can support a stronger understanding of species’ vulnerability while building capacity and collaboration to increase climate change readiness.

Postrelease Mortality of Angled Tarpon in Puerto Rico

AbstractTarpon Megalops atlanticus is a popular and economically important inshore sport fish in Puerto Rico, and the pursuit of this species by local anglers and tourists contributes to the economy. This species is managed as a no‐take fishery, which aims to preserve populations by catching and releasing fish that would otherwise be subjected to harvest and removal from the population. The approach assumes minimal mortality and/or reduced fitness of released fish, yet the process of angling can produce many sublethal side effects or direct mortality. In this study, charter angling for Tarpon in the San Juan lagoon system in Puerto Rico was examined to determine postrelease mortality. Angled fish were externally tagged with acoustic transmitters and relocated periodically to determine the fate after release. Postrelease mortality was at least 4.5% (two fish observed dead) and at most 18.2% (observed dead plus classified dead based on lack of movement; confidence interval [CI] = 7.5–28.9%). Some tag loss was observed, which could have artificially elevated classified mortality estimates. Potential factors that contribute to mortality are discussed and compared to the literature. Hook type, gear action, landing procedures, and air exposure were key areas of possible improvement. Recommendations to minimize fish harm during angling include the use of heavier action gear to reduce fight time, a circle hook requirement for live bait to reduce deep hooking, maintaining fish in the water during landing and photography, and limiting air exposure to 2 min or less if fish are removed from the water.

Angler and guide perceptions provide insights into the status and threats of the Atlantic tarpon (Megalops atlanticus) fishery

Atlantic tarpon (Megalops atlanticus) support an economically important fishery, yet there is limited information on the status of their fishery and population. A survey consisting of anglers and fishing guides was administered to help address these data deficiencies and to better understand the current and historical status of the recreational Atlantic tarpon fishery. An additional goal was to assess perceived threats to Atlantic tarpon and understand what anglers and fishing guides view as priorities for improved conservation and management efforts. Respondents (n = 918 completed surveys) indicated a significant decline in fishing quality since the 1970s. Respondents perceived water and habitat quality as the greatest threats to Atlantic tarpon populations and restoration of those as the top conservation priorities. Respondents also supported regulations that prohibit harvest (i.e., catch-and-release only), increased science efforts to understand Atlantic tarpon ecology for conservation solutions, and spatial management, such as pole-troll zones (i.e., where high speed motorboat travel is prohibited). Support for conservation solutions varied between those that targeted Atlantic tarpon with spin and fly gear, with fly gear anglers having higher support for increased regulatory oversight. With individual guides losing, on average, 2–7 Atlantic tarpon per year to sharks over the last five years, shark encounters appear to be increasing and are located in areas where Atlantic tarpon seasonally aggregate, such as passes. Given the chronic data-limited situation, local ecological knowledge derived from recreational anglers and fishing guides provide an important source of knowledge for the current and future conservation of Atlantic tarpon populations.

Correction to: Assessing the potential for red tide (Karenia brevis) algal bloom impacts on Atlantic tarpon (Megalops atlanticus) along the southwestern coast of Florida

Correction to: Assessing the potential for red tide (Karenia brevis) algal bloom impacts on Atlantic tarpon (Megalops atlanticus) along the southwestern coast of Florida

Assessing the potential for red tide (Karenia brevis) algal bloom impacts on Atlantic tarpon (Megalops atlanticus) along the southwestern coast of Florida

Assessing the potential for red tide (Karenia brevis) algal bloom impacts on Atlantic tarpon (Megalops atlanticus) along the southwestern coast of Florida

Population dynamics and movements of Atlantic tarpon, Megalops atlanticus, in the Parnaíba Delta Protected Area, Brazil: challenges for local fishery management planning

Population dynamics and movements of Atlantic tarpon, Megalops atlanticus, in the Parnaíba Delta Protected Area, Brazil: challenges for local fishery management planning

Predator-prey landscapes of large sharks and game fishes in the Florida Keys.

Interspecific interactions can play an essential role in shaping wildlife populations and communities. To date, assessments of interspecific interactions, and more specifically predator-prey dynamics, in aquatic systems over broad spatial and temporal scales (i.e., hundreds of kilometers and multiple years) are rare due to constraints on our abilities to measure effectively at those scales. We applied new methods to identify space-use overlap and potential predation risk to Atlantic tarpon (Megalops atlanticus) and permit (Trachinotus falcatus) from two known predators, great hammerhead (Sphyrna mokarran) and bull (Carcharhinus leucas) sharks, over a 3-year period using acoustic telemetry in the coastal region of the Florida Keys (USA). By examining spatiotemporal overlap, as well as the timing and order of arrival at specific locations compared to random chance, we show that potential predation risk from great hammerhead and bull sharks to Atlantic tarpon and permit are heterogeneous across the Florida Keys. Additionally, we find that predator encounter rates with these game fishes are elevated at specific locations and times, including a prespawning aggregation site in the case of Atlantic tarpon. Further, using machine learning algorithms, we identify environmental variability in overlap between predators and their potential prey, including location, habitat, time of year, lunar cycle, depth, and water temperature. These predator-prey landscapes provide insights into fundamental ecosystem function and biological conservation, especially in the context of emerging fishery-related depredation issues in coastal marine ecosystems.

Evolutionary Dynamics of Two Classes of Repetitive DNA in the Genomes of Two Species of Elopiformes (Teleostei, Elopomorpha).

The order Elopiformes includes fish species of medium to large size with a circumglobal distribution, in both the open sea, coastal, and estuarine waters. The Elopiformes are considered an excellent model for evolutionary studies due to their ample adaptive capacity, which allow them to exploit a range of different ecological niches. In this study, we analyzed the karyotype structure and distribution of two classes of repetitive DNA (microsatellites and transposable elements) in two Elopiformes species (Elops smithi and Megalops atlanticus). The results showed that the microsatellite sequences had a very similar distribution in these species, primarily associated to heterochromatin (centromeres and telomeres), suggesting these sequences contribute to the chromosome structure. In contrast, specific signals detected throughout the euchromatic regions indicate that some of these sequences may play a role in the regulation of gene expression. By contrast, the transposable elements presented a distinct distribution in the two species, pointing to a possible interspecific difference in the function of these sequences in the genomes of the two species. Therefore, the comparative genome mapping provides new insights into the structure and organization of these repetitive sequences in the Elopiformes genome.

Espécies de peixes do estuário do Rio Paraíba, nordeste do Brasil

The Paraiba River estuary is the largest and most important estuary of Paraiba state, northeastern Brazil. It is under intense environmental degradation by the surrounding human population, and possibly several fish species are at risk in this habitat. Scientific sampling of the ichthyofauna started in the late 1970’s and proceeded until recently. We present a list of fish species captured in this estuary, based on voucher specimens housed at the Federal University of Paraiba collection. Four orders of Chondrichthyes and 26 orders of Osteichthyes were identified. A total of 187 fish species, including eight species of Chondrichthyes and 179 Osteichthyes, with 123 genera and 57 families were identified. Perciformes dominated in terms of richness (32 species), followed by Acanthuriformes and Clupeiformes. Comparing estuaries along the Brazilian northeastern coast and considering our large time sampling span, a higher richness would be expected. According to the IUCN Red List, Urotrygon microphthalmum is considered Critically Endangered and more seven species are classified as Vulnerable: Rhizoprionodon porosus, Rhinoptera bonasus, Megalops atlanticus, Epinephelus itajara, Hyporthodus niveatus, Lutjanus cyanopterus, and Cynoscion acoupa. Three of these species also appear in the same category in the threatened Brazilian list, all of which have declining population trends. Concerning the Elasmobranchii, Carcharhinus porosus is listed as Critically Endangered in our country and globally. This inventory organizes and broadens knowledge on the fish community that occurs in this important ecosystem, with inferences about life habits, ecological guilds and conservation status of the fish species.