Larval Growth Rates of Three Groups of Hawaiian Fishes Derived from Sagittal Otoliths

Larval growth rates were derived from daily growth increments in the sagittal otoliths for three groups of Hawaiian fish larvae: Carangids (jacks), Pomacentrids (damselfishes) and Encrasicholina purpurea (Hawaiian anchovy). These groups were selected because there were the three most abundant fish larvae collected during entrainment sampling over four years at three power generating stations on the island of Oahu in Hawaii. A total of up to one to two hundred pairs of otoliths per taxon, covering all observed larval fish sizes, were extracted and examined. Larval lengths were recorded using a calibrated optical imaging system. Double polarized lighting was used to locate the otoliths during extraction. Accurate counts of the growth increments were made from digitally stored images of each otolith. During the entire process, fish were stored in 95% ethanol to preserve otoliths and DNA. Growth rates were determined by subtracting the hatch length from the measured larval length and then dividing this difference by the estimated number of days post hatch. The species composition of the jack and damselfish larvae was determined using DNA analysis. As a result, larval growth rates were used to derive age-length relationships for the dominant fishes within each of the groups including the Hawaiian sergeant from the Pomacentrid larvae, and the yellowtail scad and golden trevally from the Carangid larvae group. Different growth rates were also calculated for the Hawaiian anchovy for warm and cooler water periods of the year. The resulting growth rates were used to separate the larvae into age classes that were then used to estimate larval mortality rates that will be used in adult equivalent modeling of the numbers of larvae entrained by each of the plants.