Seasonal variability in growth of larval Japanese anchovy Engraulis japonicus driven by fluctuations in sea temperature in the Kii Channel, Japan

Abstract

Seasonal variability in the growth of larval Japanese anchovy Engraulis japonicus was examined through otolith microstructure analysis based on the samples collected from the northern side (inner area, IA) and the southern side (outer area, OA) of the Kii Channel from April 2006 to March 2007. Growth trajectories (otolith backcalculated mean standard length of 5 day intervals from 5 days after hatch to 24 days) as well as the most recent 5 day mean growth rate of larvae before capture (G(5)) differed among months. Growth trajectories showed the same pattern as G(5). In IA, mean +/-s.d.G(5) ranged from 0.31 +/- 0.04 mm day(-1) (January) to 0.73 +/- 0.06 mm day(-1) (October). In OA, mean +/-s.d.G(5) ranged from 0.36 +/- 0.05 mm day(-1) (January) to 0.79 +/- 0.11 mm day(-1) (August). G(5) values declined from November to January and then started to increase. In general, the seasonal patterns of growth were similar between IA and OA, and a clear seasonal pattern in growth was identified. When the relationships among larval growth rate, sea temperature, zooplankton density and larval density were examined, growth rate was positively related with sea temperature in both areas and not related with the other factors. The similar pattern in growth observed between IA and OA was probably due to the low spatial variability in sea temperature compared to its seasonal variability.