Intra-day variability of vertical water structure and distributions walleye pollock eggs in the deep-sea canyons of Avacha Bay: A field experiment during the spawning period

Tidal dynamics along the shelf break and continental slope of the Kamchatka Peninsula, adjacent to the Pacific Ocean, are a significant but underexplored factor influencing the hydrological variability. This variability affects the distribution of early life stages of the Eastern Kamchatka population of Walleye pollock, a key species for Russian fisheries. Its spawning occurs mainly in the deep-sea canyons of Avacha and Kronotsky Bays. This study aims to describe the methodology developed to investigate the impact of tidally driven hydrophysical processes on pollock egg distribution, with a focus on its application in the deep-sea canyons of Avacha Bay. Two experiments were conducted in the "Central" and "Northern" canyons during the peak of pollock spawning in April 2024, coinciding with the spring tide when tidal effect on the environment is maximized. The experimental methodology was based on frequent hydrological profiling and layer-by-layer sampling of ichthyoplankton, carried out over a day. The study identified a 50-meter amplitudes of vertical oscillation of the thermocline, located at 320–420 meter between warm and cold intermediate layers, with a distinct diurnal rhythm in the "Central" canyon and semidiurnal one in the "Northern" canyon. These results highlight the critical role of tidal dynamics in shaping hydrophysical variability, which in turn potentially affects pollock eggs vertical redistribution and development in the deep-sea canyons of Avacha Bay. 

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