Ecology of the alligator gar, Atractosteus spatula, in the Vicente Guerrero Reservoir, Tamaulipas, Mexico

We provide the first ecological account of the alligator gar, Atractosteus spatula, in the Vicente Guerrero Reservoir, Tamaulipas, Mexico. During March to September, 1998, the local fishery cooperative captured more than 23,000 kg of alligator gar from the reservoir. A random sample of their catch was dominated by males, which were significantly smaller than females. Males and females had similar weight-length relationships. Relative testicular weight varied little seasonally, but relative ovarian weight showed a strong seasonal pattern that indicated peak spawning activity during July and August. Body condition of both sexes also varied in a pattern consistent with late summer spawning. Fishing for alligator gar virtually ceased from October to February, when nonreproductive individuals were presumed to move offshore to deeper water. Alligator gar fed primarily on largemouth bass, Micropterus salmoides, and less frequently on other fishes. The gillnet fishery for alligator gar in the reservoir appears to be based primarily on individuals that move into shallow shoreline areas to spawn. Males probably remain in these habitats longer than females. The dominance of largemouth bass in the alligator gar diet reflects this centrarchid's high occurrence in littoral habitats of the reservoir, and the diet of alligator gar inhabiting deeper habitats of the reservoir could be different.