|Scientific Name:||Megalops atlanticus|
|Species Authority:||Valenciennes, 1847|
|Taxonomic Notes:||Microsatellite markers demonstrated within- and among-population genetic variability. Over most of its range, genetic differentiation was subtle. Geographically isolated and peripheral populations were much more distinct. Populations from Florida, the Pacific of Panama, Gulf of Guinea, and Costa Rica, were genetically differentiated (Ward et al. 2008). It is unknown to what extent larval dispersal versus adult migrations contribute to this differentiation (Adams pers. comm. 2011).|
|Red List Category & Criteria:||Vulnerable A2bd ver 3.1|
|Assessor/s:||Adams, A., Guindon, K., Horodysky, A., MacDonald, T., McBride, R., Shenker, J. & Ward, R.|
|Reviewer/s:||Harwell, H. & Raynal, M.|
This species is widely distributed in the Western Atlantic, and it also occurs in the eastern Atlantic and on the Pacific coast of Panama, and has extended its distribution as far northward as Costa Rica, presumably via the Panama Canal. The major threats to this species are the consumptive fishery, habitat degradation and loss (especially to sexually immature individuals (0 to 9 years)) and bycatch mortality. The substantial loss of habitat, large directed recreational fisheries throughout its range, and evidence of regional declines raise concerns regarding long-term population stability. There has been no formal stock assessment of tarpon in any portion of the species' range; however, multiple lines of evidence suggest that populations of Atlantic tarpon appear to have declined from historic levels throughout their range (Adams et al. in review). Although patchy, data on total commercial landings in Central and South America show large historical declines. Total global landings of M. atlanticus declined 84.5% between 1965 and 2007 (4,600 metric tons versus 712 metric tons), particularly in Brazil, and mostly during the early years of that time period, reflecting a drop in population size, not a change in fishery effort (FAO 2011). Using a generation time of 12.7 years (Froese and Pauly 2008), the estimated decline in FAO landings over three generations (38 years, from 1969 to 2007) is at least 60%. Although this decline is driven largely from regional commercial harvest, specifically landings from Brazil, the major trends in population are mirrored in landings data from other regions, albeit from a much smaller magnitude. In the United States, this species is regulated and over the last decade, populations in Florida appear to have remained stable; however, earlier records are statistically unreliable. Anecdotal evidence from recreational fisheries in Florida and Texas (pre-1990) suggest significant declines. Therefore, we infer that the global decline in abundance is at least 30%. This species is currently listed as Vulnerable under A2bd. Additional information about the direction and magnitude of regional population trends will warrant future attention.
|Range Description:||Megalops atlanticus is widely distributed in the western Atlantic from Virginia (there have been records from Nova Scotia), southward along the Gulf of Mexico and Rio de Janeiro, Brazil (Zale and Merrifield 1989, Crabtree et al. 1995). In the eastern Atlantic, it is distributed along the west coast of Africa, from Mauritania south to Angola (Anyanwu and Kusemiju 2008). Adults have been observed off the south coast of Ireland (Twomey and Byrne 1985). This species has also become established on the Pacific coast of Panama and has extended its distribution as far northward as Costa Rica, presumably via the Panama Canal (Swanson 1946).|
Native:Angola (Angola); Anguilla; Antigua and Barbuda; Bahamas; Barbados; Belize; Benin; Bermuda; Brazil; Cameroon; Cayman Islands; Colombia; Congo; Congo, The Democratic Republic of the; Costa Rica; Côte d'Ivoire; Cuba; Dominica; Dominican Republic; Equatorial Guinea; French Guiana; Gabon; Gambia; Ghana; Grenada; Guadeloupe; Guatemala; Guinea; Guinea-Bissau; Guyana; Haiti; Honduras; Ireland; Jamaica; Liberia; Martinique; Mauritania; Mexico; Montserrat; Namibia; Netherlands Antilles; Nicaragua; Nigeria; Panama; Portugal; Puerto Rico; Saint Kitts and Nevis; Saint Lucia; Saint Martin (French part); Saint Vincent and the Grenadines; Sao Tomé and Principe; Senegal; Sierra Leone; Sint Maarten (Dutch part); Suriname; Togo; Trinidad and Tobago; Turks and Caicos Islands; United States; Venezuela; Virgin Islands, British; Virgin Islands, U.S.
|FAO Marine Fishing Areas:||
Atlantic – eastern central; Atlantic – northeast; Atlantic – northwest; Atlantic – southeast; Atlantic – southwest; Atlantic – western central; Pacific – eastern central
|Range Map:||Click here to open the map viewer and explore range.|
In general, current estimations of abundance for this species are based on anecdotal evidence from the recreational fishery. In Florida, anglers suspect significant regional declines over the last 30–50 years, and anecdotal reports suggest declines compared to historic levels. Little scientific evidence exists to corroborate this. An analysis of the recreational Tarpon fishery in southwest Florida from 1902 through 1998 indicated that a decline in Tarpon captures began after the mid-1930s with a notable decrease during World War II (1941–45). The erratic pattern observed in this fishery could be attributed to the changes in social/recreational aspect of anglers recording data on a Tarpon scale or a decline in Tarpon landed by this fishery. There are no data currently available to test these two hypotheses. There is anecdotal information that the characteristics of the fishery changed from landings to catch-and-release, and there was a decline in recorded landings (White and Brennan 2010, Guindon 2011).
Similar to the reports from Florida, a decline was also observed in Texas in the late 1950s, although this decline appeared to be more dramatic (Ward pers. comm. 2011), and continued in the 1960s and 1970s (Winemiller and Dailey 2002). However, length modes did not decline over time as observed in Florida (Holt et al. 2005). Mechanisms for apparent declines may include habitat degradation and overfishing.
Florida state regulations granted Tarpon gamefish status in 1953, so they could not be commercially harvested or sold. By the 1970s, taxidermy was a booming million-dollar industry and Tarpon were killed routinely for mounts (Wade and Robins 1973), but the number of fish mounted each year began to decline in the mid-1970s (Crabtree unpublished data in Guindon 2011). In 1989, a new law was enacted and the harvest of Tarpon became regulated by Florida Statute. The number of harvest permits issued declined from 961 in 1989 to 280 in fiscal year 2009–2010, indicating a greatly reduced intended harvest, and a shift to a fishery that is almost entirely catch-and-release (Nelson 2002, Florida Fish and Wildlife Conservation Commission, unpublished data). In more recent years (1981–2010), most recreational catches of Atlantic Tarpon in the USA occurred along the Gulf of Mexico coast. Applying Florida sales of harvest permits to the Marine Recreational Fisheries Statistics Survey data for Tarpon caught and released in Florida, (personal communication from the National Marine Fisheries Service, Fisheries Statistics Division 2011), indicates that less than 1% of the total catch is harvested (Guindon 2011).
Over the last decade, populations in Florida appear to have remained stable; however, earlier records are statistically unreliable (Marine Recreational Fisheries Statistics Survey, National Oceanic and Atmospheric Administration 2011). One of the few estimates of a regional population of Atlantic Tarpon came from Boca Grande Pass. An acoustic survey was done in 1993, which estimated the Tarpon population in the Pass during peak spawning season to be between 24,700 and 25,400 individuals (Hedgepeth et al.1993). No similar data has been collected nor another population estimate made for this area since this study to determine whether or not abundance has increased or decreased. As this species is not primarily subjected to commercial fisheries, stock assessments have not been carried out throughout its range. Stock assessments or landings records in other parts of this species' range do not exist at present, particularly in developing countries.
Although more of the fishery appears to be trending toward catch and release, historically high levels of harvest (followed by dramatic declines) and continuing harvest in some areas, suggest cause for concern. In addition, M. atlanticus is a periodic species (Winemiller and Rose 1992), long-lived and late to mature, with correspondingly long generation length (>10 years), which may affect its resistance to and recovery from threats. Species with long generation lengths have correspondingly high population recovery time and are thus typically more susceptible to threats that cause population declines (Collette et al. 2011).
|Habitat and Ecology:||
The latitudinal distribution of Atlantic Tarpon is limited by sensitivity to low temperature (Zale and Merrifield 1989); in the extremes of their range, Tarpon experience winter thermal mortality circa 10ºC (Robins et al. 1977) and have an upper lethal thermal limit of 40ºC (Moffett and Randall 1957). Megalops atlanticus is tolerant of wide ranges in salinity and oxygen concentrations. Post-metamorphic juveniles are euryhaline, having been sampled from 0 to 45 PSU. The vascularized swim bladders of Tarpon allow aerial respiration, permitting juveniles to inhabit hypoxic inshore waters where they presumably experience low predation rates and have little competition for prey (Schlaifer and Breder 1940, Geiger et al. 2000, Seymour et al. 2004). Juvenile M. atlanticus habitats include stagnant pools, back waters, ephemeral coastal ponds and hurricane and storm overwashes, swales, and mangrove swamps and marshes, as well as man-made habitats such as mosquito impoundments and artificial wetlands (Dahl 1965, Wade 1962, Robins et al. 1977, Zerbi et al. 2001, Jud et al. 2011). These habitats are often extremely fragmented, which may have adverse effects on the population. Research is needed to document whether these habitats are sources or sink.
Late juvenile Tarpon utilize deep-water habitats such as canals and sloughs for emigration to coastal bays (Hunt pers. comm. in Kushlan and Lodge 1974). Adult tarpon (120 cm FL) are primarily coastal fishes that inhabit inshore waters and bays over a wide range of salinities (fresh to hypersaline) and temperatures (17–36°C) (Zale and Merrifield 1989, Crabtree et al.1995).
Tarpon may have resident, migratory, or mixed populations (Robins et al. 1977). Tagging studies indicate that some mature tarpon may undertake substantial and alongshore migrations (Ault et al. 2005, Luo et al. 2008), while others are residents of particular locations (Guindon unpublished data, sensu Robichaud and Rose 2004). These movements may represent repeated migratory patterns, or there may be significant annual variation in the movement pattern of individuals (Ault et al. 2008). Seasonal migrations may also occur. Migrations cross state and federal boundaries, which may impact regulation.
Juveniles start on a diet of zooplankton, small crustaceans, and insects (Harrington 1958). As older juveniles and adults begin to inhabit deeper-water habitats such as lagoons, creeks, canals, their diet transitions to larger crustaceans (penaeid shrimps, swimming crabs), polychaetes, and a suite of fishes as they grow (Whitehead and Vergara 1978, Boujard et al. 1997).
Reproduction and Development
Tarpon are batch spawners, and spawning season appears to vary by location. In Florida, spawning occurs presumably offshore from April through August (Smith 1980, Cyr 1991, Crabtree et al. 1992, 1995). Spawning in Costa Rica may occur year-round (Chacon-Chaverri 1993, Crabtree et al. 1997), similar to Puerto Rico, where peaks occur in March through May and July through September, respectively (Zerbi et al. 2001). In Brazil, spawning probably occurs from October through January (de Menezes and Paiva 1966). However, tarpon larvae have been recorded in the Gulf Stream through November (Harrington 1966), so spawning season may be prolonged or larvae may be transported long distances from more southern spawning locations. To date, active spawning events have not been directly observed.
Schools of gravid tarpon migrate from near-shore and inshore habitats to form large prespawning aggregations approximately 2–25 km offshore (Crabtree et al. 1992) presumably before moving up to 200-250 km offshore for spawning. The exact timing, cues, and zones of tarpon spawning have not been described, although it may be triggered by lunar cycles (Crabtree et al.1995).
Eggs and leptocephalus larvae have an extended oceanic planktonic stage (Phase I) followed by recruitment into fresh and brackish water nursery areas. Phase II begins at the onset of metamorphosis where larvae shrink in size from about 26 mm to 14 mm. Phase III is reflected by positive growth again through cycloid scale formation and is finished upon tarpon reaching sizes of ca. 40 mm in length (Harrington 1958,1966; Harrington and Harrington 1960). Phase II and Phase III larvae and juvenile tarpon will inhabit stagnant pools, back water, salt marsh and shallow mangrove lined areas that are low in dissolved oxygen and high in organic matter (Dahl 1965, Robins 1977, Zerbi et al. 2001). Metamorphosis is believed to take place in inshore waters. Age at recruitment to the estuary is 30–50 days (but recruiting larvae 20 days old have been captured in the Indian River Lagoon, Florida (Shenker et al. 2002).
Age and Growth
Threats to this species include effects of catch-and-release fishing (lethal and sub-lethal) (Guindon 2011), recreational harvest, commercial and subsistence fisheries in locations outside of the United States, habitat loss, freshwater flow alterations, declines in water quality, run-off, habitat fragmentation, and habitat alternation, such as dredging, and temperature extremes. This species is long-lived, which may affect its resilience to and recovery from threats.
In Texas, a study done by Holt et al. (2005), reported that there was no obvious decline in length modes with time among tarpon caught in the recreational fishery. It was indicated that larger tarpon tended to be caught in more recent years, this may be evidence of size selectivity by the fishers to retain larger fish for display or acknowledgement. The results of this study indicated that there may be a lack of recruitment of tarpon into the Texas fishery, especially from Mexico, after 1960, perhaps indicative of decline in nursery habitat. Alternatively, this could be due to natural fluctuations in recruitment.
Evidence of over-exploitation was observed in the southwest coast of Florida, in the decline in average length in the catches (Bortone 2008). Moreover, inshore waters where juvenile tarpon occur (Shenker et al. 2002) are subject to habitat degradation due to increased human activities (Bortone 2005). It should be noted, however, that Bortone used scales largely collected and posted from 1910–1930; very few scales were from collections after 1980. This coincides with a marked shift in Florida in the 1970s and 1980s towards a catch-and-release fishery (Guindon 2011).
Effects of catch-and-release fishing on tarpon has been studied in two size classes of Tarpon. Short-term, post-release mortality of adult tarpon in the recreational fishery is due predominately to predation, and to a lesser extent physiological stress and injury (Guindon 2011). In the absence of predation, estimated post-release mortality is 5% for the Gulf of Mexico coast of Florida. Other factors affecting survival of adult tarpon were the swimming condition of the tarpon at the time of release and hook location (Guindon 2011). The level of sub-lethal physiological stress was positively correlated with angling duration, handling time, and body size, especially in adult tarpon, whereas sub-adult tarpon showed less stress effects from angling (Guindon 2011). No short-term mortality was observed on juvenile tarpon released into a saltwater pond absent of sharks, and only one suffered mortality 43-hours after release. Delayed morality rates of adult tarpon are yet unknown.
Despite their ecological and economic importance, recreational fishery regulations for tarpon in the United States and abroad differ regionally. Alabama and Georgia have size limits and bag limits (one per person per day in Georgia, in Alabama a $50 tag is needed). North and South Carolina have no minimum size requirements and the limit it one fish per person per day. In Louisiana and Mississippi, there are no regulations. In Florida and Texas, a permit is required to harvest or possess a tarpon (Florida Fish and Wildlife Conservation Commission, Guindon and Ward pers. comm. 2011). In Belize, Puerto Rico, and US Virgin Islands, tarpon are catch-and-release only. In Mexico, the limit is two fish per person per day but no minimum size requirement exists.
In an effort to conserve fish stocks and their habitats, many countries are using marine protected areas in conjunction with existing fisheries regulations to build sustainable fisheries and protect marine biodiversity. Catch-and-release is commonly practised by recreational anglers with a strong conservation ethic who travel to the region. Current levels of international harvest and by-catch should be quantified, and the tertiary effects of catch-and-release fishing on tarpon should be determined to help maintain, if present, or create, if needed, a sustainable fishery.
|Citation:||Adams, A., Guindon, K., Horodysky, A., MacDonald, T., McBride, R., Shenker, J. & Ward, R. 2012. Megalops atlanticus. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 19 June 2013.|
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