Early life migration and population discrimination of the small yellow croaker Larimichthys polyactis from the Yellow Sea: inferences from otolith Sr/Ca ratios

Evaluation of Spawning- and Natal-Site Fidelity of Larimichthys polyactis in the Southern Yellow Sea Using Otolith Microchemistry

“…The otolith core is the area mostly formed during embryogenesis (i.e., the primordium and yolk sac stages; Zhan et al, 2016). Previous studies showed that the 4th increment appears after the first-feeding check with a distance of 20.67 ± 2.28 µm from the central nucleus; it is wide, dark, and well-defined (Li et al, 2013;Zhang T. T. et al, 2019;Song et al, 2022). The 20 µm ablation spots of the core zone were fully within the boundaries of the embryonic stage, indicating that the deposition of elements in the core zone was influenced by endogenous factors.…”

“…In addition to an unrecognized L. polyactis cryptic population, its spawning grounds also should also be considered in the design of management strategies. Previous studies have shown that spawning grounds have expanded from nearshore to offshore waters (Ding et al, 2007;Lin et al, 2008;Song et al, 2022). Despite new data on cryptic populations, biological characteristics, and the range of spawning grounds, spatial management measures, especially MPAs, have not been improved since the implementation of the national aquatic germplasm resources reserve of L. polyactis in the Lvsi fishing grounds in December 2009 (Ministry of Agriculture [MOA], 2021), and the monitoring and enforcement of protected areas have been unsatisfactory (Cao et al, 2017).…”

“…Element Sr is a key element involved in the formation of otoliths (Walther, 2019) and higher Sr:Ca ratios in the core zone have also been observed in Urophycis brasiliensis (Biolé et al, 2019), Anguilla japonica (Tzeng, 1996;Tsukamoto and Arai, 2001), Collichthys lucidus (Liu et al, 2015), and Miichthys miiuy (Xiong et al, 2015). The potential reasons for the higher Sr:Ca ratios in the core zone of L. polyactis otoliths have been summarized by Song et al (2022): (1) before hatching, L. polyactis feeds on the yolk sac and not on exogenous sources (Zhan et al, 2016); (2) Sr:Ca ratios are mainly influenced by the habitat environment (Elsdon and Gillanders, 2003); (3) during the embryonic stage of fish species, higher concentrations of protein and lower Ca could lead to an increase in the levels of other alkaline earth metals from the Ca group, such as Sr and Ba (Campana, 1999;Murayama et al, 2004). Indeed, Ba:Ca ratios, similar to Sr:Ca ratios, were also higher in the otolith core zone, which is consistent with the observation that high Sr concentrations facilitate Ba uptake into fish otoliths (De Vries et al, 2005).…”

“…Larimichthys polyactis is a typical oceanodromous fish that is born in estuaries or nearshore areas, grows and matures in nearby coastal waters, and migrates offshore to overwintering grounds (Xiong et al, 2017). Although progress has been made regarding the detailed migratory cycle of L. polyactis (Xu and Chen, 2009;Xiong et al, 2017;Song et al, 2022), understanding of its natalor spawning-site fidelity is limited, hampering the development and implementation of appropriate conservation and resource management strategies for this overexploited and highly targeted species. Based on the morphological variations and migratory routes of L. polyactis, three wild populations have been suggested to exist in the China Seas: and the East China Sea population, the southern Yellow Sea population, and the northern Yellow/Bohai Sea population (Lin, 1987;Zhang et al, 2014).…”

“…Therefore, specimens of the spawning group were all sampled in April; the gonadosomatic indices (GSI) were all at stages V or VI, confirming the spawning period. The deposition of elements in the otoliths of L. polyactis exhibits annual periodicity (Li et al, 2013;Zhan et al, 2016;Zhang T. T. et al, 2019;Song et al, 2022). Accordingly, the otolith elemental composition in the equivalent parts of the otolith can be used as a biological tracer to examine nataland spawning-site fidelity.…”