Validation of Daily Ring Deposition in the Otoliths of Age‐0 Alligator Gar

Abstract

AbstractWe validated techniques for estimating the daily age of young‐of‐the‐year Alligator Gar, Atractosteus spatula. Alligator Gar eggs were hatched and larvae were grown in aquaria and then transferred to an outdoor artificial stream. Fish were sampled from 21 d to 118 d posthatch. Sagittal otoliths were extracted from each fish, and each otolith was embedded in a clear epoxy resin. Otoliths were sectioned along a transverse plane, sanded with 600‐grit sandpaper to reveal daily rings, and then polished with 1500‐grit sandpaper. We estimated the daily age of each otolith three times, making each estimate in random order without reference to known ages. The mean of the three counts for each otolith was considered the final age estimate. Daily age estimates of 50 Alligator Gar (21–118 d old, 43–458 mm total length) were closely related to known fish ages, validating daily ring deposition. Absolute error in age estimates increased after 62 d posthatch; 68% of the estimated ages were within ±3 d of the known age through 62 d, whereas only 26% of the estimated ages were within ±3 d of the known age from 76 to 118 d posthatch. However, mean estimates for each cohort were within 5 d of known age through 104 d posthatch. Daily increments near the core were difficult to identify, but later increments were more discernable and deposited in a regular pattern. A significant relationship was also identified between fish total length and otolith radius (P < 0.01), indicating that estimates of growth histories should be reliable. We encourage researchers to utilize our aging technique to estimate hatch dates, the timing and frequency of hatching, and early growth rates of Alligator Gar in wild populations. This early life history information will be valuable in enhancing management and conservation of this species.Received March 21, 2014; accepted July 16, 2014