A Method for Differentiating between the Migrating Population Complexes of Sea of Okhotsk Pink Salmon in Pacific Waters off the Kuril Islands Based on the Gonadosomatic Index

Abstract

An original method is proposed for rapidly differentiating between regional pink salmon runs with different timings of spawning and states of gonads (gonadosomatic indices, GSI). The results of differentiation obtained by the original and traditional methods are compared. The concept of spatial niches for various temporal groups of Sea of Okhotsk pink salmon in Pacific waters off the Kuril Islands is critically revised on the basis of the proposed new method. The existing concept is based on the traditional use of certain numerical markers (GSI) for samples at the sites of trawl hauls. The width of the spatial overlap zone in the distribution of temporal groups is shown. The method was tested using data of trawl surveys conducted aboard the R/V Professor Kaganovsky in May–July 2018, during the anadromous migration of pink salmon. It shows high agreement with the estimates of the proportions of the contribution that the regional pink salmon groups make to the runs and catches according to the official statistics on fishing and the escapement of spawners to rivers. The assumption on the tendency of the late-maturing pink salmon forms to migrate through the southern part of Pacific waters off the Kuril Islands is confirmed. The specific (along transects) and cumulative portion of early-maturing pink has been shown to increase with distance off the Kuril straits into Pacific waters.