One tarpon population (or stock) exists in the Atlantic Ocean. A combination of adult migrations and larval dispersal, carried in prevailing ocean currents, maintain the high regional connectivity.
How can gene flow occur over such great distances?
Two life history traits of tarpon likely maintain the high levels of population connectivity we observed across the region. First, adult tarpon are capable of long-distance migrations (tagged fish have been documented traveling more than 1700km). During this study, several long-distance recaptures were identified. Three fish first caught and sampled by anglers in Florida waters were recaptured by different anglers along the Alabama and Louisiana coasts more than three years later. These migrations increase genetic mixing, as fish from several areas likely converge on the same spawning sites.
Second, tarpon larvae can be transported great distances by ocean currents. This dispersal of young tarpon also increases mixing, as larvae originating from different spawning sites may settle in the same inshore location. The connections don’t have to be direct, they can occur in step-wise fashion: a tarpon larvae spawned in Cuba may end up in Belize, where it grows up and spawns and its larvae are transported to Florida. This connects Cuba, Belize, and Florida tarpon populations. It’s important to note that it only takes a few percent of mixing between locations in each generation to result in a single population or stock.
Warm ocean surface currents in the region flow in a clockwise path, resulting in the movement of larvae among areas. Additionally, the South Equatorial Current (SEC) flows West from Africa towards Brazil and the southern Caribbean. Despite the distance between Africa and South America, the data reveal genetic connectivity in tarpon. This may occur through larval dispersal via the SEC and rare adult migrations, though migratory pathways have not been studied in the Southern Caribbean and Eastern Atlantic.