Hydrological regime in the lower reaches of spawning rivers Shumnaya and Kohmayuri (Paramushir Island, northern Kuril Islands)

Hydrological regime was explored in the lower reaches of two spawning rivers located on the western (Okhotsk Sea) coast of Paramushir Island: the Shumnaya and Kohmayuri. Water quality was examined by BLE-C600 multifunctional tester, dissolved oxygen content was measured by JPB-70A portable oximeter, and samples of bottom soil were collected on the spawning grounds closest to the river mouths. Granulometric analysis of the samples was conducted in laboratory, with the size fractions separation by dry method, using the sieves KP-131. The water parameters and fractional composition of soil correspond to conditions suitable for reproduction of pink and sockeye salmon in both rivers. Entries of pacific salmon were observed during the hydrological surveys on August 3, 2022 and July 25, 2024; active run of sockeye salmon occurred in both dates, which prevailed over pink salmon spawners.