August 2021

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Figure 1. iTAG acoustic receiver arrays along the Gulf of Mexico

B y C a r e y G e l p i P h . D. E c o s y s t e m L e a d e r, S a b i n e L a k e M a r i n e L a b

FIELD NOTES

EARS IN THE WATER,

LISTENING FOR OUR FAVORITE FISH Over the next two years the Texas Parks & Wildlife Department and Texas A&M University at Galveston will partner to expand an acoustic tagging study of southern flounder and spotted seatrout into Sabine Lake. This study will be funded through the Gulf States Marine Fisheries Commission Inter-Jurisdictional Fisheries Program. The acoustic receivers deployed in Sabine Lake will be part of a system of acoustic arrays called the iTAG network (Figure 1) that now exists across much of the US Gulf of Mexico (Gulf ) coastline, including estuaries in proximity to Corpus Christi, Matagorda, and Galveston Bays. These acoustic arrays give management agencies and academic researchers the ability to gather information about fish movement within local habitats as well as long-distance migratory patterns. This Sabine Lake array will help fill a blind spot in the western Gulf between Galveston Bay, Texas and Barataria Bay, Louisiana where there is currently a large area without receivers. Sabine Lake is unique among the estuaries that are found along the Texas coast because not only does it receive more freshwater than any other Texas bay system, with inputs from the Sabine and Neches Rivers, but also the shape of the estuary makes it an ideal location for setting up an acoustic receiver system to track fish migration. Sabine Pass, the long narrow opening to the Gulf of Mexico, is particularly suited for placing acoustic receivers. It is roughly ten km long and one km wide and is the only direct way for fish to move from Sabine Lake into and out of the Gulf of Mexico. If a tagged fish enters or leaves the estuary, then well-placed acoustic 36 | August 2021

receivers within this narrow inlet will capture that information. Sabine Lake itself is long and somewhat narrow with numerous bottlenecks where it joins with the surrounding marsh and riverine habitat. Acoustic receivers will be strategically placed throughout the estuary and nearshore Gulf, which will monitor fish movements and residency within multiple habitat types, including the Salt Bayou Marsh to the west of Sabine Lake, the Sabine Lake Oyster Reef, the Sabine and Neches Rivers, multiple bayou tributaries connecting Sabine Lake to the Sabine National Wildlife Refuge to the east, and nearshore structure possibly including new artificial reefs that are now being developed (Figure 2). The acoustic tags, which have a battery life of one to two years, are surgically implanted into the fish’s abdomen and any fish with a tag passing within approximately 0.5 km of a receiver will register the date and time of day and that fish’s unique identifier (Figure 3). Periodically, the research team visits each receiver and downloads the data, which can now be done wirelessly using the newest model of receivers. One cool and useful feature of the iTAG network is if a fish from one area happens to leave and migrate within range of receivers placed in other systems then that fish’s information will be recorded and uploaded to a shared database that can be accessed by others in the iTAG network. That way researchers not only get information about local movements within their acoustic receiver array but can also gather data on long-distance movements of fish tagged from their study area. Acoustic tagging studies provide information about


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