REPRODUCTIVE-BIOLOGY OF THE ENDEMIC GOBY, LENTIPES-CONCOLOR, FROM MAKAMAKAOLE STREAM, MAUI AND WAIKOLU STREAM, MOLOKAI

Constant pressure in Hawai'i to use limited freshwater resources has r esulted in increasing concern for the future of the native stream faun a. Hawaiian freshwater gobies have an amphidromous life cycle with a m arine larva period and require streams which flow continuously to the ocean for the critical reproductive periods and during recruitment. As such, the stream fauna is particularly sensitive to any anthropogenic perturbations which disrupt the continuity of stream flows. The objec tive of this 2-year study was to compare the life cycles of the goby, Lentipes concolor, from a heavily diverted stream on Moloka'i and a re latively undisturbed stream an Maui. In Makamaka'ole Stream, Maui, the population of L. concolor was reproductively active all year with fem ales potentially spawning 2-3 times annually. The timing of spawning d id not occur consistently during the wet or dry season but coincided w ith high stream now conditions regardless of time-of-year. In Waikolu Stream, Moloka'i, the reproductive pattern was more variable with the number of reproductively active females ranging from 0% to 100%. In ge neral the number of eggs was greater and egg size smaller for female L . concolor in Waikolu Stream than in Makamaka'ole Stream. However, fem ale reproductive condition of L. concolor from Maul was consistently h igher than from fish on Moloka'i. Reproduction of L. concolor in Makam aka'ole Stream was correlated with the seasonal pattern of flow rates with peaks in female reproductive condition associated with periods of elevated discharge. No correlation between reproduction and discharge occurred in Waikolu Stream. There were considerable differences betwe en the magnitude of discharge in the two streams. Waikolu Stream exper ienced prolonged periods of extremely low flows which have become comm on since the Moloka'i Irrigation System began diverting water from the stream in 1960. In Makamaka'ole Stream, L. concolor was capable of re producing throughout the year and adjusting fecundity in response to s tream flow conditions. In contrast, the population in Waikolu Stream a ppeared to have a 'boom or bust' reproductive pattern; the population had reduced or no reproduction when stream flow conditions reached ext reme low levels, but the population succesfully reproduced during high er flow months. The diversion structure in Waikolu Stream has dampened the natural seasonal discharge cycle, exacerbated natural low now con ditions, and increased the likelihood of prolonged periods of extremel y low flow. Stream management practices in the Hawaiian Islands must t ake into account the complex life cycles and sensitivity to variable s tream flow conditions of the native fauna.