Reproductive Biology and Egg Abundance of the Yellowtail Scad or 'Omaka, Atule mate (Carangidae), in Kane'ohe Bay, Hawai'i

Abstract

Yellowtail scad or 'omaka, Atule mate (Cuvier & Valenciennes), spawn mostly between March and September or October, but there is considerable interannual variation in length of the season and egg density in Kane'ohe Bay. Spawning occurs principally in open areas of the bay, with highest egg abundances in the southern section. Almost all adult 'omaka taken in the bay were reproductively active. More than two-thirds were males, which also routinely reached sizes larger than the largest female. Sex ratio and proportion of impending or recent spawners among females differed between day and night samples; all females in day samples were actively spawning. Adults probably move into the bay only for spawning and thus represent a biased sample of the sex ratio and spawning frequency of the population associated with the bay at any given time. Batch fecundity of females 188-232 mm standard length ranged from 63,000 to 161,000; mean relative fecundity was 741 eggs per gram. The standing stock of 'omaka associated with the bay during the peak spawning season is probably at least 800-1600 kg or 5000-10,000 adults. Current annual catch of 'omaka in the bay is a large fraction of the estimated standing stock, but the latter could be much higher if spawning frequency were underestimated or individual fish did not spawn throughout the entire season.