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Days at large (i.e., days between initial tagging and release to the date of last recapture) for each recaptured tarpon (n = 29; each horizontal line represents a single fish). Grey shaded areas represent winter (December 1 to March 1) in the study area and we considered any individual that was tagged and released before winter and recaptured after winter to have successfully overwintered in our study area
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Early life stage tarpon (Megalops atlanticus) have been collected in the western Atlantic Ocean north of Florida where it has been assumed that individuals migrate from estuarine areas at the onset of winter because water temperature during winter is too low for survival. However, there is anecdotal evidence of juvenile tarpon present during winter...
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... The northern latitudinal range of Atlantic tarpon is primarily limited by their thermophilic physiology (Howells & Garrett, 1992;Overstreet, 1974). Estuaries in US waters that are utilized by tarpon as nursery areas extend into the northern Gulf of Mexico (GOM) and along the South Carolina and North Carolina coasts (Franks et al., 2013;Graham et al., 2017;Mace III et al., 2020;Wade, 1962), where juveniles can be exposed to lethally low water temperatures during winter months (Franks et al., 2013;Graham et al., 2017;Mace III et al., 2020;Rickards, 1968). Mace III et al. (2017) investigated the thermal threshold requirements for juvenile tarpon in South Carolina estuaries and reported that their findings, combined with all published data on the cold tolerance of juvenile tarpon, resulted in an overall mean ± S.D. minimum lethal temperature of 12.0 ± 2.8 C. ...
... The northern latitudinal range of Atlantic tarpon is primarily limited by their thermophilic physiology (Howells & Garrett, 1992;Overstreet, 1974). Estuaries in US waters that are utilized by tarpon as nursery areas extend into the northern Gulf of Mexico (GOM) and along the South Carolina and North Carolina coasts (Franks et al., 2013;Graham et al., 2017;Mace III et al., 2020;Wade, 1962), where juveniles can be exposed to lethally low water temperatures during winter months (Franks et al., 2013;Graham et al., 2017;Mace III et al., 2020;Rickards, 1968). Mace III et al. (2017) investigated the thermal threshold requirements for juvenile tarpon in South Carolina estuaries and reported that their findings, combined with all published data on the cold tolerance of juvenile tarpon, resulted in an overall mean ± S.D. minimum lethal temperature of 12.0 ± 2.8 C. ...
... The objective of this study was to examine the combined effects of water temperature and salinity on the blood physiochemical variables, osmoregulation and survival of juvenile tarpon. Experimental temperatures and salinities selected for the study (15 and 25 C, ≤2 and ≥30 ppt) were based on environmental metrics associated with reported juvenile tarpon collections in US GOM and South Atlantic coastal habitats (Graham et al., 2017;Mace III et al., 2020;Stein III et al., 2016). ...
Atlantic tarpon Megalops atlanticus are highly migratory sportfish that support recreational fisheries throughout their range. In U.S. 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 two weeks in treatment conditions, blood samples were analyzed for hematocrit, 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, hematocrit 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/hr 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). Results indicate juvenile tarpon are susceptible to low temperature, which is exacerbated by low salinity, findings useful in assessment of juvenile tarpon overwintering habitat.
... However, newly recruited juvenile Atlantic tarpon that are found within northern Gulf of Mexico and South Carolina marshes in summer and fall could be negatively impacted by extreme temperature swings indicative of climate change, with cold winter temperatures preventing their survival within shallow water habitats (Graham et al. 2017;Mace et al. 2017Mace et al. , 2018. Thermal refugia in deeper portions of a South Carolina impounded pond, however, appeared to allow some overwinter survival of juvenile Atlantic tarpon (Mace et al. 2020). This observation suggests that increasing temperatures may actually result in an expansion of nursery habitats along the southeastern US coastline. ...
... However, newly recruited juvenile Atlantic tarpon that are found within northern Gulf of Mexico and South Carolina marshes in summer and fall could be negatively impacted by extreme temperature swings indicative of climate change, with cold winter temperatures preventing their survival within shallow water habitats (Graham et al. 2017;Mace et al. 2017Mace et al. , 2018. Thermal refugia in deeper portions of a South Carolina impounded pond, however, appeared to allow some overwinter survival of juvenile Atlantic tarpon (Mace et al. 2020). This observation suggests that increasing temperatures may actually result in an expansion of nursery habitats along the southeastern US coastline. ...
Tropical and subtropical coastal flats are shallow regions of the marine environment at the intersection of land and sea. These regions provide myriad ecological goods and services, including recreational fisheries focused on flats-inhabiting fishes such as bonefish, tarpon, and permit. The cascading effects of climate change have the potential to negatively impact coastal flats around the globe and to reduce their ecological and economic value. In this paper, we consider how the combined effects of climate change, including extremes in temperature and precipitation regimes, sea level rise, and changes in nutrient dynamics, are causing rapid and potentially permanent changes to the structure and function of tropical and subtropical flats ecosystems. We then apply the available science on recreationally targeted fishes to reveal how these changes can cascade through layers of biological organization—from individuals, to populations, to communities—and ultimately impact the coastal systems that depend on them. We identify critical gaps in knowledge related to the extent and severity of these effects, and how such gaps influence the effectiveness of conservation, management, policy, and grassroots stewardship efforts.
... While mechanisms of decline vary, chronic disturbances make these habitats, and their faunal constituents, prone to establishment by invasive and range-expanding species. Indeed, seagrasses now support a number of novel, warm-water consumers: Sea Bream Archosargus rhomboidalis (Seyoum et al., 2020), blue crab Callinectes sapidus (Johnson, 2015), Common Snook Centropomus undecimalus (Purtlebaugh et al., 2020), Grey Snapper Lutjanus griseus (Hare et al., 2012), Tarpon Megalops atlanticus ( (Mace et al., 2020), Ornate Wrasse Thallasoma pavo (Encarnacão et al., 2019), among others. ...
A warming climate is driving the poleward expansion of tropical, subtropical, and temperate plant and animal distributions. These changes have and continue to lead to the colonization of novel organisms into areas beyond their historical ranges. While the full scope of ecological impacts remains unclear, these expansions could alter density-dependent interactions, habitat occupancy patterns, and food web dynamics– similar to exotic species impacts in invaded ecosystems. Seagrasses are habitats of particular interest, given their widespread distribution and ecosystem services. While multiple recent studies report on the effects of the return of larger tropical herbivores in seagrass beds in warming subtropical waters, less is known about the addition of mid-trophic level consumers. These consumers are often key determinants of energy and nutrient transfers from basal resources to higher order predators. Here, we discuss the potential impacts of these distribution changes on temperate and subtropical seagrass communities using information derived from invasive species studies. Notably, we outline several scenarios and generate predictions about how their establishment might occur and speculate on impacts of warmer water consumers as they move poleward. We also discuss potential confounding factors of detecting changes in these consumer distributions. Following the invasive species literature, we offer a framework for generating hypotheses and predicting effects from these range-expanding organisms. Given that climates are predicted to continue to warm into the future, thus facilitating additional species expansions, our goal is to guide future research efforts and provide information for rapid dissemination and utility for this growing subdiscipline of marine ecology.
... We believe the juvenile tarpon collected during this study were all age-0 for multiple reasons. Winter water temperatures in most of South Carolina are below the minimum threshold for survival except in unique habitats which provide thermal refuges (e.g., thermally stratified upland pond; Mace et al. 2020). In addition, no tarpon were collected at any sites until mid-to late summer (suggesting no overwintering). ...
There is a paucity of information on juvenile tarpon Megalops atlanticus habitat use at the northern edge of its distribution. Therefore, we investigated the timing of recruitment and the size distribution of juvenile tarpon in natural and managed marshes in coastal South Carolina. We monitored recruitment to salt marsh habitats during July through November 2019 in the North Inlet estuary, Kiawah Island, and Tom Yawkey Wildlife Center Heritage Preserve. One-hundred and two juvenile tarpon (36–333 mm standard length) were observed during July to November. Tarpon from natural marsh pools (North Inlet estuary; mean ± SD = 65.4 ± 20.2 mm) were smaller than those from managed impoundments (Kiawah Island and Yawkey Preserve; 253.9 ± 41.6 mm), with no overlap in size across habitats throughout the study duration. Mean tarpon length was relatively constant throughout the study in marsh pools (65 ± 20.2 mm SL), but mean tarpon length increased from 180 ± 9.9 mm SL in August to 290 ± 31.5 mm SL in October in managed impoundments. Peak catch-per-unit-effort occurred during August (marsh pools) into September (managed impoundments) across habitat types and declined as water temperatures decreased at the end of October to November. The absence of size overlap between habitats and increasing size of tarpon over time in marsh impoundments compared to the minimal change in length over time observed for marsh pools suggests that (1) tarpon are transient in marsh pools early in life, (2) tarpon do not enter impoundments until reaching a certain size, (3) small juvenile tarpon are cryptic in impoundments and larger juvenile tarpon are more susceptible to capture in those habitats, or (4) a combination of (1), (2), and (3).
... Recent conservation and restoration initiatives have focused on identifying, evaluating, and restoring nursery habitats that occur among coastal wetlands (i.e., salt marshes and mangroves) and have identified growth as a metric to evaluate habitat quality (Adams et al., 2014Schulz et al., 2020). However, multiple year classes of juvenile tarpon occupying the same habitat (Kurth et al., 2019;Mace et al., 2020), and protracted spawning by tarpon complicates investigations attempting to understand relationships between habitat characteristics and juvenile tarpon growth in the absence of validated age and growth estimation methods. For example, presumed age-0 juvenile tarpon exhibit a large range of lengths during late fall (65 ->300 mm, standard length) throughout the southeastern US, and this varies across locations and between habitats within locations (Mace et al., 2018;Kurth et al., 2019;P. ...
... After PIT-tagging, tarpon were injected (intraperitoneally) with oxytetracycline (OTC; Duramycin-100 containing 100 mg OTC/mL, Durvet, Blue Springs, Missouri, USA) at 0.075 mg OTC/g of body weight to establish a fluorescent mark in hard structures, which served as a time stamp (Alhossaini and Pitcher, 1988). Tarpon were then placed in a holding tank for 24 h for observation prior to being stocked into an upland pond with suitable temperatures for tarpon to live year-round (33.336160, − 79.207762;Mace et al., 2020). Additionally, six fish were injected with OTC using the same methods as above to evaluate the incorporation of the OTC into tarpon hard structures. ...
... The majority of the tarpon marked with OTC and stocked were presumed age-0 because (1) winter water temperatures in the study area are below the minimum threshold for survival (~13 • C) except in a small, semi-isolated habitat suitable for overwintering (e.g., thermally stratified pond (Mace et al., 2017(Mace et al., , 2020), (2) tarpon are not present in South Carolina until mid-to late-summer (Mace et al., 2018), (3) despite extensive sampling and examination of scales and otoliths only one tarpon > age-0 has been collected from habitats where the majority of tarpon were sampled (that fish was a tagged fish that migrated from the above mentioned pond where overwintering does occur). Assuming that most stocked fish were age-0 and had not completed their first growing season at the time of stocking, an annulus should not have formed prior to injecting the fish with OTC. ...
Much emphasis has been placed on challenges related to estimating ages of old fish, yet accurately estimating age for young individuals has proved equally challenging for some species. Indices of recruitment are often based on assigning ages to young fish to estimate the strength of a given year class. Similarly, growth is most commonly estimated using age-based methods and has been proposed as a metric for evaluating the quality of nursery habitats. Unfortunately, there is a paucity of information on the validity of age estimates for many fishes, and thus the accuracy of age-based metrics used to guide management of these species is unknown. To address such needs, we conducted a validation study of age and growth estimation methods for juvenile tarpon (Megalops atlanticus), using oxytetracycline to chemically mark otoliths and scales. Oxytetracycline marks were observed on all the otoliths of recaptured tarpon (n = 23), prior to a newly formed annulus, validating true age and that one annulus is deposited yearly. Marginal increment analysis indicated that annuli form in tarpon otoliths and scales during March–April. Annuli in scales were more easily identified by readers leading to more accurate and precise estimates of age from scales (100 % accuracy of age estimates for age-1 fish) compared to otoliths (88 % accuracy). Although annual age estimates were accurate, we observed substantial error and low accuracy for daily age estimates based on otoliths (10 % accuracy). Additionally, there was a poor relationship between otolith radius and tarpon length (R² = 0.46), which resulted in inaccurate estimates of back-calculated length-at-age and growth rates. Our results indicate that scales can be used to differentiate between age-0 and age-1 tarpon, which will aid in conservation efforts by allowing for more accurate evaluation of the age structure within nursery habitats and the quality of these habitats. Further research is needed to better understand factors influencing daily age and growth estimates from otoliths.
... In Puerto Rico, Zerbi et al. (2001) analysed sagittal otoliths from young tarpon and reported the age of leptocephali at estuarine arrival, calculated juvenile age and growth rates and validated the daily deposition of growth increments for juveniles using oxytetracycline marking techniques. Recruitment and habitat use (Mace et al., 2018), thermal threshold requirements (Mace et al., 2017) and overwintering capabilities along with age and growth estimates (Mace et al., 2020) have been reported for young tarpon along the South Carolina coast. ...
... Juvenile tarpon were collected during August-December, which coincides temporally with studies at similar latitudes (Mace et al., 2018(Mace et al., , 2020Stein et al., 2016) but is abbreviated compared to studies conducted in more tropical zones (Cianciotto et al., 2019;Wilson et al., 2019;Zerbi et al., 1999Zerbi et al., , 2001. The median fork length of juveniles in the present study increased during summer and fall into winter, and the allometric length-mass relationship was similar to other studies that reported on a similar size range (Rickards, 1968), indicating these individuals used coastal habitats for post-recruitment growth. ...
... The current study examined age-0 fish only during the first growing season and may explain the higher growth rates. Conversely, studies which used tag recapture methods(Mace et al., 2018(Mace et al., , 2020Wilson et al., 2019) derived growth rates from samples which included individuals that experienced multiple seasons and low winter-temperature conditions when growth is expected to be slow or non-existent(Cyr, 1991;Mace et al., 2018;Rickards, 1968). Because of F I G U R E 9 Lunar periodicity of backcalculated hatch dates for Megalops atlanticus leptocephali (all years combined) with kernel density estimates overlain as a dark line ( ) New Moon ( ) Full Moon this seasonal variation in growth rates, comparisons drawn among studies should consider the timing and seasons of collections, along with annual temperature variations for specimens older than 1 year. ...
Age and growth of early life stage Atlantic Tarpon Megalops atlanticus collected from Mississippi coastal waters in the northcentral Gulf of Mexico are described using otolith microstructure analysis. Tarpon leptocephali (n = 95, 16.0—27.8 mm standard length; LS) collected from June through October, 2013—2018 ranged in age from 22—43 days (mean = 30.9 ± 0.5 days). Leptocephalus somatic growth rates ranged 0.46—1.24 mm day⁻¹ (mean = 0.76 ± 0.02 mm day⁻¹), and leptocephalus otolith growth rates ranged 1.78—3.97 μm day⁻¹ (mean = 2.58 ± 0.04 μm day⁻¹). Growth rates were inversely correlated to leptocephalus age, indicative of the shrinkage phase associated with leptocephalus metamorphosis. Juvenile tarpon (n = 358, 50—359 mm fork length; LF) were collected from August through December, 2007—2018. Juveniles exhibited a positive allometric relationship (adjusted R² = 0.99, P < 0.001) between length and mass. The age of 100 juveniles (71—277 mm LF) ranged from 76—174 days. Juvenile growth rate was estimated as 1.56 ± 0.11 mm day⁻¹. Significant (P < 0.001) linear relationships were found between juvenile age and otolith metrics, including otolith mass (R ² = 0.81) and radius (R² = 0.68). Evaluation of the back-calculated hatch dates suggests that specimens in the collection hatched from late May through mid-September with slight peaks during July and August. A Rao's Spacing Test of Uniformity indicates the presence of significant lunar periodicity in leptocephalus hatch dates (n = 95, U = 250.1, P < 0.05), with 50% of the leptocephali hatched within five days (before or after) of the full moon. This study fills critical gaps in the scientific knowledge of tarpon and provides estimates of early life history metrics for an iconic game fish at the northernmost extent of its Gulf of Mexico range.
... The marsh impoundments were sampled weekly from May to November 2019, and the upland pond was sampled monthly from December 2019 to June 2020. The upland pond also was sampled consistently (approximately every other month) from January 2016 to October 2018 to collect data on juvenile tarpon (Mace et al. 2020), but no snook were collected during those efforts. Juvenile snook were collected from the upland pond using hook and line, and from the impoundments using a cast net (1.8-m diameter with 6-mm mesh). ...
... Nursery areas for other subtropical fishes have been expanding in recent years. For example, juvenile tarpon have been found to overwinter in the same pond where snook overwintered (Mace et al. 2020), and anglers commonly report juvenile tarpon throughout the year in waters of southern South Carolina (M. Kimball, pers. ...
... Snook nurseries are probably the most important habitat to identify and protect because saltmarshes lie at the interface with urban development where habitat losses occur (Schulz et al. 2020) or have been impounded for mosquito control and water-level management for avian wildlife (Mace et al. 2018). This study, and similar work on juvenile tarpon (Mace et al. 2018(Mace et al. , 2020, has made progress on this topic, but more widespread sampling across the types of habitats studied here (e.g., ponds among saltmarsh, impoundments) is required to identify nursery habitats being used in South Carolina. Continued investigation into the habitat use and growth of snook, and other subtropical species with similar life histories, at this latitude could provide information regarding mechanisms that enable range expansion as the climate changes. ...
Given recent trends of warming water temperatures and shifting fish distributions, detecting range expansion is important for resource management and planning. The subtropical common snook Centropomus undecimalis (hereafter referred to as snook) is an estuarine species that historically extended from the tropics to southern portions of Florida and Texas, but this range has been expanding for the past decade. We collected juvenile snook (n = 16; size range = 96–210-mm standard length [SL]) in saltmarshes of South Carolina, which is well outside their usual range but not unprecedented. Growth rates of juvenile snook in South Carolina (0.72-mm SL d−1) were similar to those reported for Florida during a cold period, but faster than rates reported for Florida during a recent period of mild winters (0.49-mm SL d−1). Based on collection and estimated hatch dates, and supported by winter water temperature records, juvenile snook overwintered for at least 1 year allowing them to grow to sizes that are typical for emigration from nursery habitats to open estuarine shorelines. Continued work is needed to determine whether there is potential for ongoing range expansion of snook to the region, and a strategy is proposed to focus on future research.
