Spatial Organization of the Spawning Area of the Masked Greenling Hexagrammos octogrammus (Hexagrammidae) in the Northern Part of the Sea of Okhotsk

— The underwater studies of the typical spawning ground of the masked greenling Hexagrammos octogrammus conducted in the northern part of the Sea of Okhotsk at a depth of 0.8–3.0 m revealed the confinement of the species to the biotopes of rocky underwater plateaus in the macrophyte belt during the spawning season. The average density of males was 0.17 ind./m 2 . The sites with the optimal conditions for spawning of greenlings are located in the central part of the macrophyte belt (1.5–1.7 m) on medium-sized boulders. Of the three size groups of males (total body length 20–23 cm) and small (11–15 cm), significant differences in the conditions were noted only between large and small ones. Small males were located at shallower depths and closer to the shore line. Large males were located on the horizon with the dominance of brown algae at the lower boundary of macrophytes. The medium-sized greenlings (16–19 cm) showed preferences which were characteristic of both small and large individuals. An assessment of the abundance and distribution of males of masked greenling and a description of the environmental conditions at the spawning grounds (data on relief, sediments and macrophytes) made it possible to characterize the spatial organization of the spawning grounds of this species.