Projects

Using acoustic and satellite telemetry to track movements of Alabama’s state saltwater fish, Atlantic Tarpon (Megalops atlanticus)

End Date: 02/28/15

Objectives

Alabama fisherman have demonstrated that tarpon are present in Mobile Bay, Ala., for a short and specific period of time during their migration along the Gulf of Mexico, yet outside of these anecdotal reports, we know very little about tarpon movement. With the cooperation of the Alabama CCA, we successfully applied acoustic tags to tarpon sampled in Mobile Bay during 2013. This technology will allow us to ask specific questions, such as what areas are tarpon using while in Mobile Bay? How long are they residing in Mobile Bay? Despite our success applying acoustic tags to these adult fish, we know not where these fish go once they leave our acoustic array. Specifically, where do adult tarpon go once they leave Mobile Bay on their westward migration? Do they return to Mobile Bay on an eastbound migration back to Florida? Given these questions, our objective is as follows:
Objective: To apply advanced telemetry technology to adult tarpon in Mobile Bay to investigate fine-scale (acoustic tag) and large-scale (PAT tag) movement patterns.

Methodology

Sampling
Tarpon will be captured using hook and line techniques in cooperation with experienced, local tarpon fishermen with whom we’ve previously sampled. During the time that tarpon are present in Mobile Bay (June-September, Noel Nelson pers. Communication), we will conduct weekly sampling with local fisherman. Captured tarpon will be tagged with both an acoustic and satellite tag via a stainless steel dart tag (Floy tag, Inc.). The satellite tag used is similar to the model used on the only other satellite tagged tarpon in Alabama (Ault et al. 2008). Each fish will be tagged, measured, and released in good condition. All work will be conducted off the side of the fishing vessel and the tarpon will remain in the water through the duration of tagging.

Telemetry
Acoustic and satellite telemetry will be used to assess small and large scale movement patterns of tarpon. The acoustic array will consist of Lotek Wireless Inc. receivers deployed as part of CAAMP. Two types of hydrophone receivers will be deployed: 1) Lotek Wireless Hydrophone System (WHS) 3050, which detects a MAP acoustic signal (76.8 kHz) and 2) Lotek WHS 2000, which detects R code (69 kHz) transmission. Hydrophones will be placed at the mouths of rivers and bays surrounding Mobile Bay and Mississippi Sound, AL to ensure that major corridors to the estuaries are monitored. In total, seven WHS 3250 and 15 WHS 2000 acoustic receivers will be deployed around Mobile Bay. The acoustic tags used are multi-mode transmitters (Lotek MM-MR-16-50) emitting both the R code and MAP code. Each tag generates code specific pings whereby information about a tagged animal (tag number, date and timestamp) is recorded to the receiver. Data can then be downloaded from the hydrophone providing information about the time period the animal was in the area, as well as an estimated position of the tag. A Lotek Wireless PAT (model LAT3400), which records temperature, pressure and light, will be used simultaneously with an acoustic tag to provide location information from the fish once it leaves Mobile Bay. The tag will be programmed to pop-off after one-year, at which point it will float to the surface and begin transmitting data.
 

Rationale

Atlantic tarpon (Megalops atlanticus, hereafter tarpon) are a highly migratory and highly prized sport fish throughout the Gulf of Mexico (Ault et al. 2008). Tarpon exemplify the life history traits that exacerbate population declines, including slow growth, large sizes (>2 meters), old ages (>50 years) and late onset of sexual maturity (8-12 years) (Crabtree et al. 1995, Andrews et al. 2001). Tarpon make extensive seasonal and regional migrations along the Gulf of Mexico as part of their complex life history (Ault et al. 2008, Dailey et al. 2008). Although this fish is a highly prized sport fish, little is known about the ecology of this species (Ault et al. 2008). While there is evidence of historical population declines throughout their range, there has been no stock assessment of tarpon to date (Adams et al. 2013). Given the paucity of information on tarpon ecology, there is a clear need to investigate and understand the movement patterns and habitat utilization of this large fish.

Telemetry is a valuable tool used to collect data from mobile marine organisms. The major benefit of telemetry is that data can be collected remotely without the need to recapture the tagged animal (Block et al. 1998, Sedberry and Loefer 2001). Several different types of telemetry are commonly used in the marine environment. For example, acoustic telemetry allows for examination of fine scale movement patterns and habitat usage of marine fishes (Heupel et al. 2006) while satellite telemetry can be used to assess large scale movement patterns (Block et al. 1998). A pop-off archival transmitting (PAT), a particular type of satellite tag, has recently been used to track movement patterns and habitat use of tarpon off the coast of Florida (Luo and Ault 2012, Hammerschlag et al. 2012). This same tag type was also deployed on a tarpon in Mobile Bay, Ala., in September of 2007. Data from this tag showed that the tarpon left Mobile Bay shortly after it was tagged and swam along the coast of Florida until it reached Shark Bay three months later (Ault et al. 2008). While useful information, this single individual was likely tagged along its eastward migration and return to Florida; thus, we know nothing about its early season movement. Despite being Alabama’s state saltwater fish, very little is known about movement patterns of tarpon in the coastal waters of Alabama.