Study alligator gar habitat use, movement

Christopher Anderson . . . An Escambia River alligator gar. The broad, blunt, and relatively short snout distinguishes alligator gar from other gar species. (Florida Fish and Wildlife Conservation Commission)
Christopher Anderson . . . An Escambia River alligator gar. The broad, blunt, and relatively short snout distinguishes alligator gar from other gar species. (Florida Fish and Wildlife Conservation Commission)

Research shows unique fish will move a long way in late spring

Somewhere in a flood-plain pond or stream near you, alligator gar may be — or should be — spawning. I say “should be” because populations of this fearsome-looking, ancient fish are greatly reduced from their historical levels.

Their decline, and in some areas their demise, has resulted from harvest and habitat alteration. Information about habitat use and movement is critical to the species’ conservation. Recent studies in Arkansas and Florida provide useful information.

Biology of a beast

Alligator gar are long-lived, primitive fish that grow to sizes exceeding 7 feet and 200 pounds. They live in larger rivers and oxbow lakes and can tolerate brackish water. Spawning occurs in May and June in Mississippi waters.

Although insufficiently studied to define specific spawning habitat requirements, spawning has been observed in a variety of flood-plain ponds, oxbow lakes, and tributary streams. The eggs are deposited on brush or aquatic vegetation.

Adults are primarily fish eaters, but fish in coastal marshes also eat blue crabs. They are stalking predators, usually seen lurking in or near brush or marginal vegetation.

While several species of gar are called “gator gar,” the broad and blunt snout of alligator gar is an easy way to distinguish them from others members of the gar clan.

Escambia River

The Escambia River flows through the Florida Panhandle into Pensacola Bay. Florida Fish and Wildlife Conservation Commission biologists tracked adult alligator gar, 37 to 76 inches long, in the Escambia River for two years. Alligator gar concentrated in off-channel habitats in the winter, sometimes with individuals only several feet apart. As water temperature warmed above 60 degrees in April, the fish dispersed into the main channel. Throughout the year, the tracked fish largely remained in the middle and lower reaches of the Escambia, where they had access to off-channel habitat.

The fish moved little during the cold season, but they moved more frequently and greater distances from April to November, when movement averaged 27 miles among individual fish. The longest distance moved was 63 miles. Movement did not differ between day and night in either the warm or cold seasons.

Fourche LaFave River

The Fourche LaFave River flows through west-central Arkansas, ending at the Arkansas River. The University of Central Arkansas and U.S. Fish and Wildlife Service fisheries biologists tracked alligator gar 59 to 88 inches long from February to October for two years in the lower reaches of Fourche LaFave.

During the February-to-April prespawn period, alligator gar were located primarily in slow-current depressions in the main channel of river. Rising river stages and inundation of the flood plain in May was accompanied by alligator gar moving downstream toward known spawning areas, then moving onto the flood plain and into flood-plain tributaries to spawn. The flood-plain tributaries were used more frequently than the inundated flood plains.

Alligator gars have gills like other fish, but they also have a swim bladder that is connected to their stomach by a unique duct that allows them to gulp air from the surface. This also allows them to live in water that a low level of dissolved oxygen. Oh, and the teeth are pretty interesting. (Florida Fish and Wildlife Conservation Commission)
Alligator gars have gills like other fish, but they also have a swim bladder that is connected to their stomach by a unique duct that allows them to gulp air from the surface. This also allows them to live in water that a low level of dissolved oxygen. Oh, and the teeth are pretty interesting. (Florida Fish and Wildlife Conservation Commission)

Distances and speed of movement were lowest during the cold-water, prespawn season and increased during the spawn; spawning-season movement was confined to movement within and among the spawning areas. The Arkansas research team suggested the frequent movement near the spawning areas may be a consequence of the gar monitoring the water and habitat conditions, waiting for the best conditions for spawning. The fish distributed extensively upstream and downstream of the spawning areas after the spawn.

Except for the brief period of the spawn, alligator gar were most-frequently located in the main channel of the Fourche LaFave River. The fish usually were within 15 feet of the channel bank in relatively shallow water with slow or no current. Fish were more often located in areas with overhanging vegetation and in-water structure, like logs and fallen trees, than in open water or areas with only overhanging vegetation or in-water structure.

Implications for conservation

Whether in Arkansas, Florida or other states where alligator gar live and have been studied, the fish need access to slow- or no-current areas in the winter and inundated flood plain or off-channel areas during the spring spawn. From the information available, rising water in the spring seems to be an important trigger for spawning. And the rising water must occur at a time that coincides with the normal spawning cycle.

Slack-water areas appear to be critical wintering habitat. While alligator gar remaining in the channel of the Fourche LaFave River may seem to contradict this, Fourche LaFave River has little flow, and the flood plain has little inundated habitat in the winter.

Changes to the landscape that alter the amount and timing of river flows and channelization or levees that eliminate access to floodplain or off-channel habitat can be expected to threaten the persistence of this ancient fish. The relatively limited movement of these fish suggests that local habitat management and system-specific harvest restriction may benefit recovery of alligator gar.

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About Hal Schramm 147 Articles
Hal Schramm is an avid angler and veteran fisheries biologist.