Do early growth dynamics explain recruitment success in Japanese flounder Paralichthys olivaceus off the Pacific coast of northern Japan?

Abstract

We examined the relative importance of growth-related processes operating during the larval and early juvenile stage in explaining variability in year class success of Japanese flounder off the Pacific coast of northern Japan. Early growth trajectory of larvae and juveniles sampled in 2005 (strong year class) and in 2006 (weak year class) was estimated from the analysis of the lapillar otolith. The larval pelagic stage was characterized by lower growth and developmental rates, as well as high selection for fast growth in the metamorphosis/settlement period, during the strong recruitment event of 2005 relative to 2006. Growth appeared higher in 2005 only after settlement despite high density in the nursery, which likely reflected superior productivity during that year combined with an increased probability of cannibalism from early settlers on late settlers. This implies that larval growth dynamics did not play an important role in determining recruitment strength in the two years considered. The decreasing distance from the nursery areas of pelagic larvae through ontogeny in 2005, combined with low age at settlement, suggest that larvae benefited from positive transport conditions during the dominant year class. To the contrary, unfavorable hydrographic conditions likely prevailed in 2006 as distance from the nurseries increased with ontogeny and settlement occurred later than in 2005 despite faster growth potential and developmental rate. We conclude that transport conditions to the nursery grounds, rather than larval growth potential, represented the most important determinant of year class success in the two years considered.