Consumer-grade side-scan sonar has become a versatile fisheries management tool. First applied to assess habitat, its use has expanded to surveying fishes in recent years. However, an important consideration is the skill and experience of users, which can impact both the accuracy and comparability of surveys. To this end, we characterized the ability of a small sample of novice users (N = 8) to identify alligator gar Atractosteus spatula in imagery, as well as the effect of a two-hour training exercise on user performance. Prior to training, mean accuracy (expressed as the difference between observed and expected counts) among participants ranged from -2.6 to 1.3 fish and precision ranged from ± 1.2 to 2.4 fish, with the majority of participants underestimating the number of alligator gar present in the imagery. False positives (i.e., identifying alligator gar in imagery when none were present) were common among participants. Post-training mean accuracy ranged from -3.1 to 0 among participants and precision ranged from ± 1.6 to 3.2 fish. The frequency of false positives was significantly reduced following training, and participants reported significant increases in confidence associated with image interpretation. The relatively high accuracy and precision we observed prior to training indicated that side-scan sonar can be easily incorporated into large-scale fishery monitoring efforts for alligator gar. However, our results also suggested that a rather minimal investment in training can further improve consistency and reduce uncertainty among novice users.
First record of exotic alligator gar, Atractosteus spatula (Actinopterygii: Lepisosteiformes: Lepisosteidae), from Ganga River system, India: A possible threat to indigenous riverine fish diversity
