Population connectivity of small yellow croaker (Larmichthys polyactis) in the southern Yellow Sea: Implications from multiple otolith-based approaches

Connectivity is a fundamental aspect governing the viability of marine species populations, particularly during their early life stage. However, a dearth of comprehensive studies exists regarding connectivity patterns in Larmichthys polyactis within the southern Yellow Sea region. To address this gap, we conducted a thorough investigation into the population connectivity of L. polyactis collected from Haizhou Bay (HZB) and Lvsi (LS) fishing grounds, employing a suite of otolith-based methodologies. Initially, our analysis of otolith microstructure revealed a notable incubation peak occurring between early and mid-April for juvenile L. polyactis sampled in HZB, despite the sea surface temperature (SST) during that period not aligning with the known spawning requirements of L. polyactis. By juxtaposing the spawning period and associated SST conditions of L. polyactis across different fishing grounds, we deduced a high likelihood that the HZB samples originated from the LS. Subsequently, we investigated the stable isotope ratios (δ¹³C and δ¹⁸O) of L. polyactis collected in HZB, LS, and offshore locations, focusing on the core zone indicative of the early life stage. Statistical analysis using Dunn's multiple comparison test revealed that no significant disparity in otolith δ¹³C and δ¹⁸O values between HZB and LS samples (P > 0.01). However, these values were notably lower than those observed I n offshore samples (P < 0.01). Furthermore, through otolith morphological analysis, we identified two distinct aggregations within the HZB samples, one aligning with the entirety of the LS samples and another representing the remaining HZB sample subset. This finding provides additional support for the population connectivity between HZB and LS stocks. Drawing upon these findings, we posit the existence of a a mixed population of L. polyactis within HZB, likely resulting from the transportation of eggs or larvae originating from LS to HZB via prevailing northward currents. An enhanced understanding of connectivity dynamics among L. polyactis holds significant implications for the formulation of effective management strategies aimed at bolstering stock recovery efforts.