Rodgers et al. 1992

Rodgers, J. D., M. F. Solazzi, S. L. Johnson, and M. A. Buckman. 1992. Comparison of three techniques to estimate juvenile coho salmon populations in small streams. North American Journal of Fisheries Management 12(79-86).

Mark-recapture, removal, and snorkel population estimates were compared with a known number of juvenile coho salmon Oncorhynchus kisutch stocked in 18 pools in the same stream during the summer. The effects of fish density, pool size, and habitat complexity on the percentage of the actual population estimated by the three methods were examined. Mark–recapture estimates were also compared with known numbers of juvenile coho salmon stocked in six pools in the same stream during the winter, and snorkel counts were compared with mark–recapture estimates obtained in other Oregon coastal streams during the summer and winter. After all pool sizes and fish densities were combined, during the summer 85% of the actual number of fish present were accounted for by mark–recapture, 67% by removal, and 40% by snorkel counts. Summer pool surface area explained 44% of the variation in the accuracy of mark–recapture estimates. Pool surface area and the percentage of the pool volume taken up by rootwads explained 73% of the variation in the accuracy of removal estimates. None of the physical variables measured explained a significant portion of the variation in the accuracy of snorkel estimates. During the winter, mark–recapture estimates accounted for 87% of the actual number of fish present. The percentage of fish estimated by mark–recapture that were observed by snorkeling was lower and more variable in winter than in summer. We could not account for a significant portion of this variability with any of the 17 physical variables measured.