Watershed-scale patterns of seaward migration in Lentipes concolor, a Hawaiian stream goby

Abstract

The native stream fishes of the Hawaiian Islands are uniquely adapted to colonize and thrive in lotic habitats in this extremely isolated archipelago. Chapter 1 of this dissertation introduces the five native fishes of Hawaii's streams and describes the variety of lotic habitats they occupy. All five species have amphidromous life cycles, and, as such, their larvae must migrate to the ocean soon after hatching. Of the five species, Lentipes concolor is able to scale Hawaii's highest waterfalls during the migration back into fresh water, and therefore inhabits the widest variety of stream types. Adult L. concolor are found a few meters from the ocean in small streams that enter the ocean as terminal waterfalls. Lentipes concolor also inhabit inland stream reaches located at high elevations in large streams with low gradient terminal estuaries. This dissertation examined potential spatial and temporal patterns in the migration of newly hatched L. concolor larvae as they passively drifted from instream hatching sites to marine habitats. Results presented in Chapter 2 demonstrated that more larvae successfully completed seaward migration in terminal waterfall streams than did larvae spawned in the upper reaches of larger, higher-order streams. In Chapter 3, a significant diel drift pattern was observed during 24-hour sampling. Although larvae were captured in drift nets during both day and night, a preponderance of larvae during the first three hours following sunset was the most commonly observed trend. Results presented in Chapter 3 also suggest that in terminal-waterfall streams, spawning and therefore downstream movement of larvae occur more commonly during new-moon phases. A lack of distinct lunar periodicity in upland reaches of large streams is hypothesized to possibly be related to the high frequency and intensity of flash floods that may disrupt the sequence of courtship and spawning behavior of adult L. concolor. Chapter 4 discusses ways in which the new information contained in the previous two chapters may change current paradigms regarding the population ecology and conservation of native stream fishes in Hawai'i.