Chum salmon (Oncorhyncus keta) is a cold-water species reported to migrate within a wide range of habitats, including Korea, Japan, North America, and Russia, playing important roles in the river–sea nutrient cycle and food web. However, research on this species has not been widely performed in South Korea owing to its geographical location at the southern edge of migration. In this study, we analyzed the spatial distribution and morphological characteristics of chum salmon migrating to South Korea using the length–weight relationship. We also analyzed 3 years of catch, sex ratio, and individual information (total length (cm), weight (kg), n = 4400) from ten rivers (eight in the East coast and two on the South coast) with a total of 17 years of water quality and the distance they traveled (n = 50) using multivariate analysis. As a result, we discovered a trend of less migration in the southern part of South Korea for all individuals migrating to South Korea. Furthermore, the weight ratio of males/females was significantly different (p < 0.05). Based on the length–weight relationship analysis, the a and b values were between 0.0011 and 0.038 and 2.65 and 3.49, respectively. In the correlation analysis, catch is negatively correlated with distance traveled and temperature (p < 0.05), and positively correlated with pH, dissolved oxygen, distance, and female ratio (p < 0.05). This is possibly the result of differences in water quality during early life stages or the presence of an estuarine barrage at the mouth of the Nakdong River. This research may be used as fundamental distribution and morphological variations of chum salmon in South Korea.
eDNA extracted from the gut contents of filter feeders with unique feeding habits can be used to identify biodiversity in aquatic ecosystems. In this study, we used eDNA from the gut contents of the clam Corbicula fluminea to examine estuarine ecosystem biodiversity. The field survey was conducted at three study sites in the Nakdong River Estuary, which is characterised by closed estuarine features resulting from the presence of an estuarine barrage. The collected C. fluminea samples were dissected to separate the gut contents, and the extracted eDNA was amplified using the 18S V9 primer targeting all eukaryotes. The amplified DNA was sequenced using next generation sequencing (NGS) techniques, and BLASTn was performed based on the NCBI database. We obtained 21 unique operational taxonomic units (OTUs), including fish (approximately 9.52%), copepods (approximately 14.29%), and green algae (approximately 23.81%), which represented a wide range of habitats such as marine, brackish, freshwater, and terrestrial environments. These results suggest that various organisms living in aquatic ecosystems can be identified through eDNA from the gut contents of C. fluminea and support the potential application of bivalves as eDNA samplers in diverse aquatic ecosystems.
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