Larval Pacific anchovy Engraulis japonicus were sampled from coastal waters off the central west coast of Korea from June to November 1996. Using otolith microstructure analysis (daily growth increments), three cohorts (spring, early summer and late summer) were distinguished based on backcalculated spawning dates. Growth rates differed between cohorts, with higher growth rates for late-summer cohorts than either the spring or early-summer cohorts. Growth rate was positively related to surface water temperature, with an optimum temperature range of between 20 and 26°C occurring during the late summer (late July through to mid-September). The study highlights that early growth rates of Pacific anchovy are dependent on ecosystem (particularly water temperature) attributes during early life.
The age, growth, and maturity of chub mackerel Scomber japonicus were determined by otolith analysis and gonad observation. Fish were subsampled monthly from Korean offshore commercial catches between September 1994 and August 1995. Gonad observations suggest that chub mackerel spawned mainly in May. The size at 50% maturity was calculated to be 28.8 cm fork length at an age of 1.01 years. Annuli in otoliths can be distinguished from false annuli because the true annuli were formed continuously all around the sagittal plane as distinct dark marks. They were mainly formed in May, coinciding with the main spawning season. Chub mackerel grew to over 20 cm by December and attained up to 28 cm in 1 year. Thereafter, the growth rate slowed down. The age composition was 40.2, 42.5, 15.4, 1.7, and 0.1% for age‐groups 0–4, respectively. Using three different approaches, the von Bertalanffy growth parameter was estimated to be between 1.51 and 2.19 and the maximum length between 34.1 and 34.6 cm. The growth coefficient was higher than that in previous studies because of differences in aging technique and the inclusion of juvenile data in one of the approaches. Over 40% of the immature fish of age 0 were included in the current harvest owing to the catch of juveniles in summer and strong fishing intensity in autumn. We recommend regulating catch size during the fast‐growing stage to allow the juveniles to grow and reducing the fishing efforts during autumn to conserve the spawning biomass.
The Japanese eel Anguilla japonica is an important aquaculture fish species in the East Asian countries of Japan, China, Korea, and Taiwan. All glass eel fry are captured from the wild and understanding the recruitment patterns of the glass eel is important. The larvae of A. japonica are passively transported to the East Asian Continental Shelf by the North Equatorial Current, the Kuroshio, the Kuroshio intrusion currents, and coastal currents. In each location, recruitment time is diverse: It is November in Taiwan and April in the Yalu River. How the glass eels reach recruitment areas remains poorly understood. Here, we combine information from larval ages based on otolith increments, simulated drifting paths on the East Asian Continental Shelf, and main fishing seasons in each location of East Asia. We identify five main recruitment blocks: (1) The main Kuroshio, (2) The Taiwan Strait Warm Current, (3) The Taiwan Warm Current, (4) The Yellow Sea Warm Current and (5) The branch of Yellow Sea Warm Current. The counted age of the glass eels is significantly underestimated for the later recruits, possibly due to the cessation of the otolith edge growth under low water temperatures. This study clarifies the eel’s larval characteristics and transport mechanisms in the East Asia Continental Shelf, providing important information for its recruitment dynamics in the marine stage.
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