Patterns of growth in the early life history of the round herring Etrumeus teres

Abstract

Early life history traits of young‐of‐the‐year (YOY) round herring Etrumeus teres, caught in Tosa Bay (south‐western Japan), were studied using otolith microstructure analysis for the 2000–2003 year classes. Hatch dates ranged from October to March, and were restricted to either autumn or winter within each year class. YOY ranged from 50 to 123 mm total length (LT) and from 57 to 192 days in age. The relationship of LT to otolith radius was linear. Individual growth rates (GI) were backcalculated between the 70th and 150th days (the size range of most YOY caught) using the biological intercept method. GI ranged from 0·3 to 1·4 mm day−1 and decreased in most cases as season progressed irrespective of year class, although GI in winter cohorts were significantly higher than in autumn cohorts. Otolith growth rates (GO) ranged from 2·13 to 12·25 μm day−1 for autumn spawned YOY and from 3·12 to 12·41 μm day−1 for YOY spawned in winter. The GO trajectories followed three consistent patterns: (1) an increase in increment widths after first feeding through the second week of larval life, then (2) a plateau in increment spacing before increment widths increased again until reaching the maximum growth rate, followed by (3) a gradual decrease in increment widths until the end of the fifth month. The three stages occurred irrespective of spawning season, although YOY spawned in October and December had higher GO during stages (1) and (2) than YOY spawned in February and March, whereas higher GO was observed for late‐winter cohorts in stage (3). Otolith growth from YOY spawned in December and January showed an intermediate pattern between YOY hatched in the early autumn (October to December) and late winter (February to March). The GO trajectories were cross‐matched to the calendar date to estimate time series of otolith growth rates (GOTS) for each year. A parabolic trend was found with maximum GOTS in autumn and spring and minimum values in winter. This trend was significantly correlated to daily sea surface temperature variations. The differences in otolith growth trajectories suggest that the otolith microstructure of E. teres may be used as a natural tag for identifying autumn and winter spawned cohorts.