Dynamics of the Reproduction Period of the Sea Raven Hemitripterus villosus (Hemitripteridae) in the Southwestern Part of Peter the Great Bay: Results of 20-Year Monitoring (1997–2016)

The reproduction period of the sea raven Hemitripterus villosus were studied by visual SCUBA-diving methods in 1997–2016 in Peter the Great Bay, the Sea of Japan. It has been found that the beginning and the end of the spawning period shifted to a later date (5–12-day shift) in particular years, which is explained by the increased water temperature at the spawning grounds by 1.6–2.5°C in September–October. The degree of damage of the open egg masses has greatly increased (from 35.2 to 60.4%), the main predator is the sea urchin Mesocentrotus nudus. The observed changes in the timing of reproduction and an increase in the degree of egg consumption by predators are not critical factors for reducing the abundance of the sea raven.