Relationship between the timing of embryonic and larval development of pink salmon and downstream migration of its juveniles

Purpose: Determine the relationship between the duration of embryonic and larval development of pink salmon ( Oncorhynchus gorbuscha ) under different temperature regimes and the timing of downstream migration of their juveniles. Research Material: Multiyear average daily data on water temperature and condition of pink salmon embryos and larvae bred in commercial volumes at the Kurilsky (Iturup Island), Lesnoy and Pugachevsky (Eastern Sakhalin) salmon hatcheries. Methods used: Comparative data analysis, descriptive statistics methods. Results: The known facts about changes in the timing of embryonic development in relation to water temperature were confirmed: The duration of the interval between the dates of hatching of embryos in the first and last batches developed under different thermal conditions was 2.5 times longer than the interval between the dates of fertilization of eggs from these batches. The extension of the embryonic development period in the last batches was accompanied by a shortening of the subsequent development period until the fry were ready to swim, which reduced the difference in the duration of development from egg fertilization to fry swimming at different temperatures. This process is not only associated with different hatching times and slowed development in the winter period. The identified peculiarities in the changes in the duration of intermediate developmental stages under different temperature regimes suggest that fry developing in colder water goes afloat as less developed. Such regulation of the total duration of embryonic and larval development of pink salmon provides mass migration of its juveniles from rivers in the average annual terms of mass development of zooplankton in the coastal sea. Practical Significance: The presented article is a scientific accompaniment of the monitoring of pink salmon juvenile downstream migration in order to forecast changes in the stocks of this species of Pacific salmon.