Water temperature induced interannual variation in spawning of Japanese Spanish mackerel Scomberomorus niphonius in the northern Yellow Sea

Japanese Spanish mackerel Scomberomorus niphonius is a pelagic, neritic species that occurs in the Yellow Sea in high commercial value. The spawning period of this fast-growing species is controlled by water temperature. Based on microstructural analysis of otoliths from 145 young-of-the-year (YoY) S. niphonius collected by trawl in 2017, 2018, and 2020, and the temporal variation in the spawning period in the northern Yellow Sea, and its relationship to water temperature were examined. We found that the spawning lasted from late April to late June but differed in year: in 2017 it occurred from April 23 to June 1 and peaked in early May, in 2018 it extended later from May 7 to June 29, and in 2020 from May 6 to June 22 and peaked later from late May to mid-June. The highest temperature in 2017 corresponds with the earliest end of the spawning period and a lower growing degree-day (GDD, degrees C center dot day) of 383 degrees C center dot day. In 2018, slower warming corresponds with a longer spawning period, and a GDD spawning period of 506 degrees C center dot day. Rapid warming in late 2020 corresponds with a spawning peak, and a GDD spawning temperature of 448 degrees C center dot day. Despite differences in spawning period, the water temperature when spawning commenced was 10-12 degrees C. Therefore, water temperature is the major determinant of the spawning period, affecting both the starting and the ending of spawning. This study improved our understanding of the spawning dynamics and environmental adaptation of S. niphonius, and how these might change in environments subject to increased warming.