Evaluation of Marking Techniques to Estimate Population Size and First-Year Survival of Colorado Squawfish

Abstract

Abstract Three marking methods-tattoo ink injected with a dental inoculator, an elastic polymer injected by syringe, and fin clipping—were tested to determine a suitable technique for estimating population size, survival, and movement of age-0 Colorado squawfish Ptychocheilus lucius. Laboratory tests indicated that all three marks were retained at sufficient rates (>97%) to make population estimates over a 21-d period. However, fish marked with tattoo ink had higher mortality (10%) than fish marked with elastic polymer (< 1%) or with a fin clip (0%). Fish marked with the elastic polymer had higher retention (85%) than those marked with fin clips (34%) or tattoo ink (26%) after 142 d. No differences in vulnerability to predation were observed among fish with the three marks or between marked and unmarked fish. A field test of the elastic polymer showed that it was easy to use, caused low mortality (5% for fish held overnight in live-cages), and produced marks that were readily visible, Mark–recapture metho...