On state of the ichthyocene in Lake Lebedinoye (Iturup Island) in autumn season

Abstract

   Spatial distribution of fish species was surveyed in Lake Lebedinoye (Iturup Island) in September and October 2025 with fry seine (20 m long, 1.5 m high, 4 mm mesh size). The ichthyocene was predominantly represented by amur stickleback Pungitius sinensis, with a small portion (up to 3–5 %) of juvenile big-scaled redfin Tribolodon hakonensis. Weight of the redfin juveniles varied from 50–100 mg to 5–6 g. Abundance of two main fish species and their ratio were rather stable by stations and during the whole period of survey. Japanese smelt Hypomesus nipponensis were presented in 18.7 % of catches, but 18–22 individuals of the species with various size were in each of these catches. Single specimens of juvenile starry flounder Platichthys stellatus were caught occasionally in different parts of the lake, which were not observed there previously, though ability of marine flounders to enter fresh water bodies is known. A juvenile of the introduced prussian carp Carassius gibelio was caught for the first time in Lake Lebedinoye that was a clear sign of this species reproduction in the lake, although very limited. Japanese huchen Parahucho perryi were not detected at the coast in September but appeared after October 7, when the water temperature at the surface of the lake did not excess 14.1 оC and dropped to 8.0 оC at the mouth of the Rybovodny stream. Besides the fish, shrimp Palaemon paucidens and mysid Neomysis awatschensis were caught occasionally in different parts of the lake; the shrimp biomass was sometimes comparable with the biomass of amur stickleback.