UNCOVERING MIGRATORY PATTERNS OF THE NATIVE HAWAIIAN FRESHWATER GOBY, ‘O‘OPU NĀKEA (AWAOUS STAMINEUS)

Abstract

Hawaiʻi is home to ʻoʻopu nākea, a culturally significant, endemic, freshwater goby that exhibits an amphidromous life history. Despite their importance in Hawaiian traditions and their ecological role in freshwater systems, we still lack understanding of their migratory patterns and life history due to the difficulties in determining the environmental factors that form their migratory paths and fish age. This study examined whether different environmental factors, such as amount of rainfall, streamflow, and water chemistry, play a role in (1) the migratory flexibility of A. stamineus and/or (2) the larval duration periods. I sampled 90 individuals from the lower, mid-, and upper-reach of three streams across a rainfall gradient on the windward side of the island of Oʻahu (Kahana, Kahaluʻu, and Waimānalo streams). Using otolith elemental analysis, I examined Sr:Ca ratios to determine if individuals spent their larval period in the ocean (migrants) or if they never left the freshwater streams (residents). I found that 89/90 of the otoliths that were adequately sampled had clear marine levels of strontium, showing very limited flexibility in an amphidromous life cycle. Migratory abilities and larval durations do not seem to be affected by the amount of rainfall a stream receives. This study is a key step in understanding the life history of ʻoʻopu nākea, and it highlights the importance of upstream, downstream connectivity for the survival of amphidromous species. Additionally, this local study of A. stamineus life history will contribute to the global knowledge of amphidromous fish species to better inform management and conservation practices to increase populations worldwide.