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Aug. 11, 2011
Alligator Gar Research in Texas Helps Protect Trophy Fishery
ATHENS — Despite being one of the largest freshwater fish species in North America, scientists knew little about alligator gar until relatively recently. In the last two decades, knowledge about the species has grown tremendously in response to evidence that alligator gar populations are declining in many areas.
The primary reasons alligator gar have declined throughout much of their historic 14-state range are loss of floodplain habitats necessary for reproduction (from reservoir construction and river channelization) and overfishing. As a result, the American Fisheries Society has considered alligator gar “at risk of imperilment” since 2008.
Texas is fortunate to still have many of the best populations of large alligator gar in the world. The Trinity River has become one of the most popular locations to fish for the species. Susceptibility to habitat loss, coupled with increased fishing pressure, prompted Texas Parks and Wildlife Department (TPWD) to adopt a one-fish per day bag limit on September 1, 2009. This made Texas the eighth state to adopt harvest regulations for alligator gar.
Alligator gar longer than six feet are considered to be more vulnerable to angler harvest due to their more desirable “trophy” size. Although alligator gar may reach three feet in length in three years, their growth rate slows with age, and the fish may take 20 to 30 years to reach a length of six feet.
Biologists have discovered that alligator gar can live more than 50 years and take about a decade to become sexually mature. It could take several decades to restore their numbers if depleted. Many states are already in the process of stocking and attempting to reestablish alligator gar populations. By setting a one-fish per day regulation, Texas inland fisheries biologists hope to prevent the decline in alligator gar populations seen in other areas.
A number of research initiatives have been completed or are underway to better understand gar populations throughout Texas. TPWD biologists have conducted studies to evaluate growth rates and life span, understand their reproduction, and track the seasonal movement of alligator gar. Biologists have also conducted studies to evaluate angler harvest rates of alligator gar and estimate population sizes.
Efforts to increase age data for alligator gar from waters throughout the state are underway by collecting otoliths from angler-caught alligator gar. Otoliths are pairs of small bones in the inner ears of fish which contain annual growth rings similar to the rings in a tree. Age data make it possible to determine how fast fish grow, how long they are capable of living, and compare historical river conditions to the year the fish were hatched.
By comparing age data with historical water levels, biologists observed high river flows during late spring can result in strong alligator gar reproductive success. For example, high river flows in 2007 resulted in a very strong year-class of alligator gar in the Trinity River. In the current drought year, alligator gar may produce few to no offspring at all. Knowledge about which environmental conditions produced the most fish will allow biologists to better predict strong and weak year classes. Biologists may also be able to work with river and reservoir controlling authorities to help provide the conditions necessary for successful reproduction.
From October 2008 through July 2010, a study on the Trinity River used acoustic tags to track the movements of alligator gar between Lake Livingston and Trinity Bay. Biologists found alligator gar were concentrated in deep pools in the main river channel for most of the year but moved to tributaries and protected backwaters during flooding. Biologists also found that although some fish moved more than 100 miles, most of the alligator gar remained within 15 miles of their tagging locations. There was little interaction between fish tagged in different parts of the river, suggesting that alligator gar near Trinity Bay may be a separate population than alligator gar near Lake Livingston Dam. Further research is needed to determine if these populations should be managed separately.
A mark-recapture study in the river between Dallas and Lake Livingston (about 200 river miles) was also conducted with the help of fishing guide Kirk Kirkland. Captain Kirkland tagged alligator gar, and TPWD recorded the number of tagged fish he and other anglers caught.
With these data, biologists estimated that this portion of the river contained about 9,200 alligator gar 42 inches long or longer and about 1,400 fish 78 inches or longer. It was determined that about three to four percent of these alligator gar were harvested annually with most (73 percent) of the harvest occurring between April and July of each year. Biologists also estimated that only about 5 percent, or 400 fish 42 inches or longer, could be harvested each year from this portion of the river and still sustain this trophy fishery.
Since 2009, 130 harvested alligator gar have been collected and aged from anglers at Trinity River bowfishing tournaments. Using information obtained from tournaments, biologists were also able to estimate harvest rates of alligator gar at the events. Only about one alligator gar was harvested for every four bowfishers at the Trinity River tournaments, and it took an average of 50 angler-hours to harvest an alligator gar at a tournament. Angers harvested an average of 21 fish each year 42 inches or longer during the three studied tournaments, or about 5 percent of the sustainable annual harvest of 400 fish. This level of harvest from tournaments alone is well below estimated sustainable levels; however, biologists still need more information to determine what total percentage of alligator gar are harvested annually outside of bow fishing tournaments and using other methods like rod and reel.
While the Trinity River is a well-known stronghold for alligator gar in the state, many Texas reservoirs, such as Choke Canyon Reservoir and Lake Amistad, also support healthy populations. TPWD began a tagging study of alligator gar in Choke Canyon Reservoir in 2011. Tags returned by anglers will provide biologists with information on harvest, abundance, size structure, and survival. In addition, recaptures of tagged fish during the spawning season will provide clues to number of spawning locations, how often fish spawn in the reservoir, and if fish return to the same locations to spawn each year.
Through the various research projects throughout the state, biologists plan to refine management objectives specific to certain rivers and reservoirs around the state to better maintain or enhance the alligator gar fisheries. Future research needs will involve further assessments of alligator gar populations around Texas to better understand fishing pressure and harvest. A population study of alligator gar in the Brazos River below Waco is currently in the planning stages. TPWD’s goal is to study and manage Texas alligator gar populations to sustain excellent fishing opportunities for this species for present and future generations to enjoy.
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