Early Life History Characteristics and Contribution of Stocked Juvenile Alligator Gar in Lake Texoma, Oklahoma

Abstract

Due to concerns of overexploitation and population decline caused by anthropogenic influences, fisheries managers have turned to hatchery produced Alligator Gar (Atractosteus spatula) stocking to supplement inconsistent wild year classes. Aquaculture can be a useful option to reestablish or supplement natural populations, as many states currently have stocking programs to reintroduce this species. Recent interest in Alligator Gar ecology and conservation has led the Oklahoma Department of Wildlife Conservation to attempt to better understand early life history
characteristics of age-0 Alligator Gar in Lake Texoma by tracking growth, diet, habitat use, mortality and stocking contribution. A total of 33,900 Alligator Gar fingerlings were stocked into Lake Texoma in 2017. During June-September 2017, a total of 46 age-0 Alligator Gar were captured in 279 net nights of effort using mini-fyke nets. Mean CPUE (catch-per-unit-effort; number per net night) was highly variable with CPUE varying based on vegetation stem density in the location of the net set. Of the 46 Alligator Gar captured in 2017, 84.5% (39 of 46) were stocked (OTC mark present). During the 4-month sampling period, the daily mortality estimate for stocked age-0 Alligator Gar was 0.049%/day. After the first four months (4.7% mortality rate), 32,306 of the initial 33,900 Alligator Gar remained in the system. The annual estimated mortality rate is 16.7%. The mortality estimate of fish stocked into Lake Texoma is substantially lower than the 94.8% mortality rate observed in the hatchery over three months (1,043 of 20,001 age-0 Alligator Gar remained). Stocking Alligator Gar as fingerlings when water level and habitat availability is sufficient may be more beneficial than holding them in a hatchery setting. Conversely, stocking Alligator Gar early may not be beneficial in a marginal year when nursery habitat is limited and inflow is not consistent enough to maintain a constant pool elevation. During these years it may be better to grow-out fingerlings to larger sizes, such that when stocked they are not easily preyed upon.