Abstract
The walleye pollock Gadus chalcogrammus is an important commercial species in Japan whose larvae and eggs may be negatively affected by the cold water mass from the coastal Oyashio current that is present in the spawning ground of the Japanese Pacific stock of this species. Therefore, we investigated egg and larval specific density, larval mortality, and behavioral response to temperature change during the ontogenetic development of the walleye pollock to understand the effect of this cold surface water mass (<1.5 °C). Egg and larval specific density varied during development but were lower than the corresponding values from the coastal Oyashio waters. Within our study temperature range (0.3–10.0 °C), the number of days to 50% mortality (D50) was high at 3.1 °C. Below and above this temperature, the D50 showed a decreasing trend. Regarding larval response, at 1.5°C and 5.0°C, newly hatched larvae occurred abundantly in the surface layer, irrespective of the surface and rearing temperatures. When these larvae were released into a thermally stratified water column (surface: 1.5 °C, bottom: 5.0 °C), larvae reared at 5.0 °C with the mouth open and yolk sac completely absorbed moved to the lower layers. However, larvae reared at 1.5 °C remained in the surface layer. These results suggest that the cold water mass could negatively affect larval survival and may limit the escape ability of larvae from unfavorable cold conditions.
Highlights
Published: 28 July 2021The walleye pollock Gadus chalcogrammus is a commercially important species in Japan with four regional stocks: northern Japanese sea stock, southern Okhotsk sea stock, NemuroStrait stock, and Japanese Pacific stock (JPS) [1,2,3,4], of which the JPS is the largest [3]
To understand the effect of the coastal Oyashio water mass on the survival and development of the eggs and larvae of the walleye pollock, we examined the following: Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
At the newly hatched stage, larvae remained in the surface layer independent of the vertical thermal pattern (Figure 6)
Summary
Published: 28 July 2021The walleye pollock Gadus chalcogrammus is a commercially important species in Japan with four regional stocks: northern Japanese sea stock, southern Okhotsk sea stock, NemuroStrait stock, and Japanese Pacific stock (JPS) [1,2,3,4], of which the JPS is the largest [3]. The. JPS spawns from December to March (mainly January–February) near the mouth of Funka. The optimal temperature range for the survival of walleye pollock eggs and larvae is 2–7 ◦ C [10]. In the latter part of the spawning season, cold water from the coastal Oyashio current enters Funka Bay, and the temperature of the surface water layer decreases (
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