Morphobiological Difference and Reproduction Peculiarities of Pink Salmon Oncorhynchus gorbuscha from Two Rivers in the Northeastern Part of Sakhalin Island

Abstract

Morphobiological indices and reproduction peculiarities of the pink salmon Oncorhynchus gorbuscha have been studied for the specimens sampled in two rivers of the northeastern part of Sakhalin Island: the Langeri River and the Malaya Khuzi River. Based on the data on the timing and intensity of the spawning run and the biometric characteristics of the breeders, three temporal groups of pink salmon corresponding to the schools originating from the Sea of Japan and the summer and autumn schools from the Sea of Okhotsk have been defined with certainty, while autumn spawning has been found only in the Langeri River. The Okhotsk summer school forms the basis of the pink salmon population. In the studied rivers, the pink salmon of all temporal schools is represented by two sympatric groups that differ in otolith nuclear zone structure and, at the same time, have no any significant differences in body size and weight nor in fecundity. It is suggested that the variability in the otolith nuclear zone structure is due to the difference in abiotic conditions at the spawning grounds during early embryogenesis.