Feasibility of Dual-Marking Age-0 Chinook Salmon for Mark–Recapture Studies

Abstract

Abstract We investigated the short-term mortality associated with the application of a dual mark on juvenile Chinook salmon Oncorhynchus tshawytscha used in mark–recapture trials. Treatment groups were either spray-dyed with fluorescent pigments, stained with Bismarck brown, or marked with both. Acute mortality was greater for the spray-dyed–Bismarck brown combination (0.48%) and the spray-dyed (0.13%) treatment groups than for the Bismarck brown or control groups. Daily mortality was less than 0.15% for marked treatment groups for 3 d after marking. Cumulative mortality was greatest for the spray-dyed (0.93%) and the spray-dyed– Bismarck brown (0.84%) groups. Significant differences in mortality were not detected among groups (P = 0.063) or within groups on a temporal scale (P = 0.124). Recognition of fluorescent pigments was 100% during the study. Bismarck brown staining did not obscure the fluorescent pigments, which were easily differentiated among colors. We conclude that our dual-marking technique provides researchers with a feasible method to differentially mass-mark fish with minimal mortality. Moreover, mark recognition is greatly enhanced.