Correcting Visual Implant Elastomer Tag Identification to Better Evaluate Adult Atlantic Salmon Returns from Multiple Stocking Sites in the Penobscot River, Maine, USA
Christine A. Lipsky, Edward M. Hastings, Russell Brown, and Richard B. Dill
Abstract.—Atlantic salmon Salmo salar smolts are stocked in the Penobscot River, Maine to supplement declining populations. Since 2000, approximately 550,000 hatchery smolts are annually released into the river, of which 32% of these (175,000) were marked with visual implant elastomer (VIE) tags indicating release time and location. Our study found that tag colors of adult returns were often misread due to confusion between green and yellow marks and between red and pink marks. Using data collected on mark readings in a controlled hatchery environment, we corrected for tag identification errors made in the field, thereby allowing adjustments to be made in the marked returns to accurately assess the number of returns from multiple stocking groups. When adult returns from multiple stocking groups were compared, significant differences were detected between stocking groups, including a three-fold difference between two of the stocking groups. Hence, a simple change in smolt stocking locations and times may be of value in the recovery of the Penobscot River salmon population.