Population consequences of mass coming of pink salmon Oncorhynchus gorbuscha to the Northeastern Coast of Kamchatka in 2009

Abstract

During mass spawning of pink salmon Oncorhynchus gorbuscha in two rivers of central Karaginskii Bay (Kamchatka), the average coverage of the spawning hillock did not vary much (0.6–0.7 m2) even though the abundance of the spawning adults varied greatly. When the abundance of spawning females was less than 1.4 ind. per m2 of spawning ground, the spawning hillocks did not interlock. When the abundance of spawning females varied from 1.7 to 1.8 ind./m2, the spawning hillocks interlocked, and approximately 20–25% of them were re-excavated. When the abundance of spawning females was higher than 2.0 ind./m2, all the early-deposited spawning hillocks were re-excavated. The re-excavation of the spawning hillocks increased the population mortality also by the mass pre-spawning death of the breeders and spawning outside the spawning grounds. Meanwhile, fish-kill of the eggs in the spawning hillocks was not observed, and the mortality of embryos and larvae did not depend on the spawning intensity. The ratio of live and dead embryos in the spawning hillocks before their hatching was approximately 60%, varying from 44 up to 92% in regard to the environment of the spawning ground (autumn low water, freezing, and siltation). Significant correlation was found between the survivability and grain-size composition of the spawning hillocks when the impact of small-size fraction was a limiting factor.