Modern methods of fish marking and their practical significance for fisheries research (case study of Pacific salmon)

This paper presents a comprehensive review of animal marking methods used in zoological and fisheries research, with an emphasis on modern identification technologies and their practical application in the study of Pacific salmon. Historical analysis shows the evolution of approaches from simple traumatic methods (fin amputation, branding, mechanical tagging) to high-tech systems, including acoustic tags, radioisotope indicators, RFID transponders of various frequency ranges, and otolith marking techniques. Special attention is paid to the classification of methods according to their operating principle, volume of transmitted information, degree of impact on the object, and the possibility of remote reading. The advantages and limitations of passive and active RFID systems, as well as the specifics of their application in the aquatic environment, are considered. Based on the analysis of long-term studies, it has been established that for the tasks of mass tagging of juvenile fish, primarily salmonids, otolith marking (thermal and dry) is recognized as the most effective and informative method, allowing millions of specimens to be tagged annually with subsequent reliable identification of hatchery origin. The practical significance of this method is confirmed by the results of coordinated otolith marking of Pacific salmon in the Russian Far East. Identification of hatchery fish in spawning aggregations of Kamchatka, Magadan Oblast, Sakhalin, and Khabarovsk Krai made it possible to obtain verified rates of commercial return for the main salmon hatcheries. In addition, marking quantitatively confirms the phenomenon of straying, which significantly distorts the assessment of the real contribution of individual hatcheries to reproduction. It is noted that currently otolith marking is the most significant method used in the organization of artificial reproduction monitoring and in the practical activities of hatcheries.