Long-term variations in body length and age at maturity of the small yellow croaker ( Larimichthys polyactis Bleeker, 1877) in the Bohai Sea and the Yellow Sea, China

This study focused on changes in the maturation schedules, as depicted in maturity ogives, of female small yellow croaker ( Larimichthys polyactis) in the Bohai Sea and the Yellow Sea during the 1960–2010 spawning seasons. The two stocks studied were the northern Yellow Sea-Bohai Sea stock (the NYBS, n = 1283) and the southern Yellow Sea stock (the SYS, n = 2024). Body length ( L 50) and age at median sexual maturity ( A 50) were estimated by an arcsin-square-root (ASR) transformative logistic model and an inverse von Bertalanffy growth function, respectively. The results show that L 50 decreased from 152.8 mm to 105.3 mm between 1960 and 2003–2005 in the NYBS and from 184.4 mm to 110.1 mm between 1960 and 2010 in the SYS. Over the same period, A 50 decreased from approximately 1.5 years in the NYBS and 2.4 years in the SYS to about 1 year in both stocks. Significant intrastock changes ( P < 0.01) in length–maturation curves were found in both stocks over long time periods (≥4 years); however, there were no significant changes ( P > 0.05) over short time intervals (