Port Aransas, Texas was once known as the “Tarpon Capital of the World” from 1920-1940
when large schools of tarpon (Megalops atlanticus) would pass along the coast. By the 1960’s
the fishery had collapsed and while overfishing played a role in the decline of tarpon along the
Texas coast, an improved understanding of the population characteristics of this species is
needed to evaluate the viability of rebuilding plans for the Texas population.
Our understanding of the origin and migration pathways of adult tarpon that frequent the
Texas coast each year is limited. Scientists assume that two primary spawning grounds exist for
tarpon in the Gulf of Mexico (Gulf), with one stock spawning in the SE Gulf around the Florida
coast and the other in the SW Gulf from Veracruz to the Bay of Campeche. Genetic evidence
indicates that most of the population present in Texas originates from Mexico; however,
genetic differentiation has been detected between tarpon collected in north and south Texas,
possibly suggesting the presence of two migratory contingents or populations. While strict
catch regulations have been implemented in U.S. waters, tarpon are regularly harvested in
Mexico, and therefore movement of tarpon across the Texas-Mexico border will likely reduce
the effectiveness of management strategies aimed at restoring population(s) in the U.S.
The primary objective of the Texas Tarpon Tagging Initiative (T3i) is to track the movements of tarpon in Texas waters using acoustic and satellite telemetry. Our research will provide critical information about short- and long-term movements of tarpon along the Texas coast, and determine the origin and residency patterns of tarpon found in the NW Gulf. We also hope to expand the scope of this research to identify essential habitats of tarpon in Texas waters and the environmental conditions that define highly suitable habitats.
Acoustic telemetry allows scientists to track tarpon for several years using a system of receivers and transmitters. T3i scientists are surgically implanting V16 acoustic tags (or transmitters; Figure 1) into the abdomen of tarpon (Figure 2), with the goal to tag over 50 individuals by 2021. As the tagged tarpon swims within range of an acoustic receiver, the transmitter emits a unique tag code (identifying the individual tarpon) to the receiver, which logs the code with a date/time stamp. Detections on multiple receivers by a tarpon will allow us to retrospectively determine the range and timing of movements, which will be used to elucidate migration pathways.
Figure 1. A Vemco V16 acoustic transmitter. All transmitters will be registered with the Integrated Tracking of Aquatic Animals in the Gulf of Mexico (iTAG) network, allowing fish that swim outside of the Texas Coastal Array to be detected by other receivers placed throughout the Gulf and possibly other locations.
Figure 2. Tarpon tagging in action off Galveston, Texas. Arrow indicates location where the acoustic transmitter was inserted.
There are currently over 30 acoustic receivers that make up the Texas Coastal Array positioned along the coast from Louisiana (near Cameron Beach) to the Texas/Mexico border. The Texas Coastal Array includes several acoustic gates or detection areas, with receivers typically placed near tidal passes within 10 km from shore (Figure 3).
Figure 3. Map of receiver locations in the Texas Coastal Array.
Tagged tarpon are also given a conventional (or spaghetti) tag near the dorsal fin. These tags have a unique ID number and the telephone number for our program. You can call or submit the information here, to report the tag number, fish length, fish girth, and location were the tarpon was caught. Recapture information from anglers helps fill in movement pattern gaps that may be missed by acoustic receivers.
Figure 4. Initial tagging locations (yellow star) and receiver detection locations (black circles) of three tagged tarpon indicating a fall southern migration, and one tarpon displaying a return spring northern migration.
As of October 2020, 22 tarpon have been tagged along the Texas and Louisiana coasts. Currently, five tagged tarpon have been detected by acoustic receivers from the Coastal Array, with three of the more interesting migrations tracks shown in Figure 4. Tarpon "8616" and "8618" were tagged in October of 2018 near Galveston. After a year of no detections, tarpon "8616" was detected off the coast of Corpus Christi in October of 2019 and then again off the coast of South Padre Island in November of 2019. Tarpon "8618" was also detected a year later near Matagorda Bay in October 2019 and then again off the coast of Corpus Christi in November 2019. The other individual, tarpon "6213", was tagged in September of 2019 near Galveston. Two months after being tagged, tarpon "6213", was detected off the coast of South Padre Island around the same time as tarpon "8616". In the summer of 2020, tarpon "6213" was detected moving north from North Padre Island to Port Aransas on the same day. The observed pathways of these individuals demonstrate a fall southern migration along the Texas coast, with tarpon "6213" exhibiting a return spring northern migration.