Relationships between the daily growth rate of Japanese anchovy Engraulis japonicus larvae and environmental factors in Osaka Bay, Seto Inland Sea, Japan

Abstract

Seasonal changes in the growth rate of larval Japanese anchovy Engraulis japonicus collected by shirasu seine net boats in Osaka Bay in 2008 were estimated using otolith daily growth increments to examine the effects of environmental factors. Larval anchovy were caught from May to November. The range in standard length (SL) of the larval anchovy was 10–35 mm, and larvae of SL 20–25 mm dominated numerically, accounting for more than 40% of all anchovy larvae. Daily growth rates for the last five days before catch increased from May to July, decreased or were stagnant in August and September, increased again in October, and decreased in November. Seawater temperature and density of copepod nauplii were correlated with the daily growth rate. In this study, the relationship between growth rate and temperature showed a skewed dome shape, with an optimum temperature for growth of around 23 °C. These results in summer of 2008 suggest that the growth rate of Japanese anchovy increased with increasing temperature for temperatures < 23 °C, but growth was limited by prey availability and/or other factors, such as low dissolved oxygen, at higher temperatures. Recent environmental improvements in nutrient inputs to Osaka Bay are discussed in relation to larval growth rate.