Growth and fatness of 1975–2002 year classes of Japanese sardine in the Pacific waters around northern Japan

摘要

We examined individual growth and fatness in the 1975–2002 year classes of Japanese sardine. Samples were collected at the feeding grounds in the Pacific waters off northern Japan during drastic fluctuations in the population in the 1970s to 2000s. Growth rates for ages 1–3 of the 1979–1988 year classes, which included low-recruitment year classes subsisting during the high population levels of the 1980s, were apparently slower than for other year classes. There was no obvious trend when comparing year classes, growth during the first year of life (age 0), and maximum body length (BL) at age ≥5. The condition factors (CF, indicating fatness) for adult sardines of BL ≥19 cm in the 1979–1983 year classes during the maximum population level of the mid-1980s were significantly lower than for other year classes. However, there were no apparent trends in CF variations for small sardines of BL <19 cm. The apparent decreases in growth rate and fatness were strongly related to the cumulative sum of population abundance that each year class experienced. It is thought that insufficient food owing to the density-dependent effect of an abundant population at feeding grounds resulted in a decrease in the growth rate for small-bodied sardines that are investing their energy intake in body growth, and a decrease in fatness for large-bodied adults that are accumulating fat for the next reproduction.