Meeting Abstract

S7-1.4  Saturday, Jan. 5  Morphological Selection in a Distinctive Flow Environment: Body Shape and Waterfall-climbing Success in Hawaiian Stream Fishes BLOB, R.W.**; SCHOENFUSS, H.L.; MAIE, T.; CEDIEL, R.A.; PTACEK, M.B.; BRIDGES, W.C.; Clemson Univ.; St. Cloud State Univ.; Clemson Univ.; St. Cloud State Univ.; Clemson Univ.; Clemson Univ. rblob@clemson.edu

Many fish species living in streams on volcanic islands exhibit an amphidromous life cycle, in which juveniles hatched in freshwater are swept to the ocean to develop before returning to adult stream habitats. In the Hawaiian Islands, juvenile gobiid fishes face two major functional demands on their return upstream: (1) avoiding predators in lower stream reaches, then (2) climbing waterfalls up to tens of meters high to reach adult habitats using specialized ventral suckers. The body shapes best suited to meet these demands should differ, with a deep body improving predator avoidance and a more streamlined body with larger suckers improving climbing success. Such shape differences are seen between fish from islands where different pressures predominate: Sicyopterus stimpsoni from Kaua�i have deeper bodies, correlated with the longer, predator filled estuaries that must be traversed before reaching adult habitats, whereas S. stimpsoni from the Big Island climb waterfalls shortly after entering streams and have more streamlined bodies. To test the potential for the flow environment of waterfalls to impose selection that could contribute to body shape differences between populations, we subjected juvenile, Big Island S. stimpsoni to climbing trials up an artificial waterfall (~100 body lengths) and compared body shape between successful and unsuccessful climbers. Nearly 30% of fish failed the climbing test. However, few significant shape differences between successful and unsuccessful climbers matched hydrodynamic predictions. Thus, climbing failure may be related to non-morphological features, and shape differences between populations may be more strongly influenced by exposure to predators.