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

The small yellow croaker Larimichthys polyactis is a benthic marine fish species of high ecological and commercial importance and is widely distributed in the northwestern Pacific Ocean, especially in the Chinese coastal waters of the Bohai, Yellow, and East China Seas. As a highly migratory species, the whole life migration of L. polyactis has been intensively studied. However, knowledge about its early life migration is scarce, and population divisions are inconsistent, limiting the ability of fishery scientists and administrators to evaluate the design and potential benefits of thorough conservation and resource-management strategies. In the present study, otolith Sr/Ca was analyzed to investigate the early migratory patterns and discriminate the populations of L. polyactis in the Yellow Sea, including two spawning groups and one overwintering group. The variation in Sr/Ca ratios of ontogenetic growth zones, including the nucleus (N), larval (L), metamorphosis (M), juvenile (J), and edge (E) zones, was measured by electron probe microanalysis. The variation in Sr/Ca ratios in early developmental growth zones was generally characterized by an evident downward trend from the N to J zone, which suggests that the early migratory pattern of L. polyactis might be from inshore to nearshore water. Canonical discriminant analysis, based on the otolith Sr/Ca ratios of the N, L, M, and J zones, allowed the successful discrimination of the two populations, namely, the northern and southern Yellow Sea groups, whose differences were mainly reflected in the L and J zones. Compared with previous studies, the traditional geographic boundaries (34°N) separating these two populations might be moving northward. The application of otolith Sr/Ca ratios based on ontogenetic stage could improve our understanding of the migration and population discrimination of L. polyactis from the Yellow Sea.