Methodological problems of quantitative assessment for downstream migrating juveniles of pacific salmon gen. Oncorhynchus in small rivers of the Sakhalin Region

Methodological approaches used in the Sakhalin branch of the Russian Federal Research Institute of Fisheries and Oceanography (SakhNIRO) for quantitative assessment of pacific salmon (Oncorhynchus) juveniles in the rivers of Sakhalin Region are analyzed critically. Methodic and logical problems are revealed that worsened the results reliability. The linear interpolation used for time correction of cross-sectional distribution for juveniles of pink salmon Oncorhynchus gorbuscha in a control river gives sometimes unrealistic negative values when actual catches are not zero, that means the algorithm has limited applicability. Ways for methodological improvements are proposed, including formalization of computing procedures, implementation of quality control at certain stages, and data verification and validation. Without these measures implementation, the current methodology does not ensure standardization of calculations, so cannot serve as a reliable basis for monitoring the juveniles abundance.