Growth effect on the otolith and somatic size relationship in Japanese anchovy and sardine larvae

ABSTRACT:  Relationships between otolith and somatic sizes were examined for Japanese anchovy Engraulis japonicus and sardine Sardinops melanostictus larvae collected broadly in the western North Pacific, based on a substantial data set derived from a previous paper. Allometric formulae showed close fits to the relationships between otolith radius and standard length, and the formulae differed between anchovy and sardine larvae. Despite the high correlations, the effect of somatic growth rate on the otolith and somatic size relationship (the ‘growth effect’) was significantly detected for both anchovy and sardine larvae. Slower growing larvae tended to have larger otoliths than faster growing conspecifics at the same somatic size. This growth effect was more obvious for sardine larvae than for anchovy larvae, probably because of their differential responses of somatic growth to temperature shifts. The growth effect could lead to the possibility of biases in the back-calculation and size estimation processes. As the growth effect is considered to be a general phenomenon and its extent to be species-specific, the relationship between otolith and somatic size and its uncoupling should be scrutinized before application of techniques based on the otolith and somatic size correlation.