Purpose. The paper is purposed at proving (based on the data of a special field experiment) the importance of vertical tidal mixing which is conditioned by the diurnal shelf waves, on the one hand, and determines the specific conditions for forming food supply for gray whales in the Marine feeding area near the Sakhalin northeastern coast, on the other hand.

Methods and Results. The materials for the research were formed of the data resulted from the instrumental measurements of current velocities, water temperature and salinity (and their variations) in the bottom layer carried out at three diurnal oceanological stations in the Marine feeding area in autumn 2019 as well as the satellite data on the chlorophyll a concentration (2003–2017).

Conclusions. The results of the diurnal station measurements showed that in the Marine feeding area of gray whales (on the Sakhalin northeastern shelf), there was a constantly working mechanism which intensified and weakened together with the diurnal tides (cycle was a half a month). It is manifested in the diurnal seawater temperature and salinity variations near the bottom, as well as in the vertical distributions of oceanological parameters. Due to the diurnal shelf waves providing local tidal mixing, the conditions contributing to the sustainable formation of food supply for gray whales arise in this area.