Genetic variation was surveyed at the mitochondrial control region (766bp) to test for the presence of genetic stock structure in the small yellow croaker, Larimichthys polyactis from the Yellow and East China Seas. Individuals of the small yellow croaker could not be distinguished on the basis of its location, as demonstrated using the neighborjoining (NJ) method, unweighted pair-group method, arithmetic average (UPGMA) and the minimum spanning network (MSN). Analysis of molecular variance revealed no significant differences among collections of the small yellow croaker taken from the four locations (two locations each in Korea and China). Neutrality tests and a mismatch distribution analysis indicated that this species has recently expanded. Our findings suggest either that the small yellow croaker has a high migration capability that enables it to overcome the effects of genetic drift, or that this species expanded relatively recently and has not yet had sufficient time to differentiate.
Four specimens of unknown Coilia sp. were collected for the first time from the Yellow Sea in 2008 and compared with Coilia mystus and Coilia nasus. Coilia sp. showed similar morphology to C. mystus and C. nasus, but differed in that its tail was considerably shorter. We conducted an analysis of the morphological and genetic characteristics in an effort to clarify the taxonomic position of Coilia sp. In counts and measurements, Coilia sp. were well distinguished from C. nasus by the number of scutes (42Á44 in Coilia sp. vs. 40Á45 in C. mystus vs. 45Á55 in C. nasus), ratio of dorsal base length to head length (43.4Á47.6 vs. 37.9Á47.6 vs. 33.0Á41.0), and eye length to head length (19.2Á20.8 vs. 17.0Á22.4 vs. 13.8Á18.2). In caudal skeleton of Coilia sp., urostyle, hypural and epural bones were not observed; instead of them, caudal fin rays were supported by the last vertebra, neural and haemal spines' extension. The molecular phylogenetic relationship was analyzed using 414 base-pair 12S rRNA mitochondrial DNA sequences. The Kimura-2-parameter distance between Coilia sp. and C. mystus was 0.3%, but was 1.3% between Coilia sp. and C. nasus. Both the neighbor-joining tree and maximum-likelihood tree showed that Coilia sp. are closely clustered with C. mystus. Therefore, our results suggest that the Coilia sp. may be a deformed fish of C. mystus.
Seasonal catch distributions of large purse seines and daily landings of coastal set nets were analyzed to understand the migration path of the Spanish mackerel Scomberomorus niphonius around Korean waters. The Spanish mackerel start to move toward the coastal region in the South and West Sea in May for spawning and stay until July, when spawning finishes. Afterwards, they start to migrate to the East China Sea and the southern East Sea and are found irrespective of the onshore and offshore regions. Therefore, they disappear from the offshore region during the spawning season in June and July, and a new recruitment population of age 0 begins to inflow into the coastal fishing grounds in the South Sea and West Sea in August, one month earlier than in the Japanese coastal region of the East Sea.
We examined monthly changes in the rate of fishes by-caught by gape net with wings and their immature ratio in the coast of Yeosu and Jindo Island, Korea. A minus correlation between bycatch rate, the ratio of fishes except for anchovy, Engraulis japonicus, to all fishes collected by gape net with wings, and individuals of the collected anchovy was significantly observed, implying that as the anchovy catch decreased and the bycatch rate increased. Immature ratios by the dominant bycatch species during the study is the following; Leiognathus nuchalis was 72.7~99.0%, Sphyraena pinguis was 84.0%, Sardinella zunasi was 90.0%, others (Leptocephalus, Trichiurus lepturus, Ammodytes personatus, Sphyraena pinguis, Trachurus japonicas, Mugil cephalus and Erisphex pottii) were 100.0%. In order to decrease the high bycatch rates of immature fishes in spring and autumn, our study suggested increasing of codend mesh size and developing suitable bycatch reduction devices in a gape net with wings.
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