Striking features of Okhotsk herring spawning Clupea pallasii in 2025 and their practical consequences

Abstract

The Okhotsk herring spawning season in 2025 had significant features. Unusually, it began at low temperatures (≤2 °C). However, embryo development at unfavorable temperatures (averaging 3.04 °C) did not result in an increase of their elimination (6.2%). The potential spawning range developed according to productive type I, but was realized according to low-productivity type IV: 2/3 of the spawning grounds were located in the northeast of the range. However, the recorded area of spawning grounds was close to the maximum (50.37 km² ), with spawning supersites extending up to 52 km and covering up to 19.7 km² . Contrary to previously identified patterns, spawning densities were unevenly distributed: an average of 1.83 million eggs/m² in the southwest and 4.23 million eggs/m² in the northeast. Population fecundity (173 trillion eggs) was close to maхimal, but spawning stock biomass fell from 2.270 million tons in 2020 to 1.789 million tons in 2025. This is likely due to the degradation of spawning grounds: the disappearance of local spawning sites, the disappearance of Zostera marina as a spawning substrate, and a 1.6-fold decrease in average specific vegetation substrate biomass. Therefore, conservative regulatory scenarios for the Okhotsk herring fishery must be adhered to in the near future. To adequately account for the stock, outdated vessels must be replaced with modern, high-speed, and highly productive ones. This is important, especially in the context of the ambiguous development of oceanographic processes in the north of the Sea of Okhotsk and their direct impact on the formation of herring replenishment.