The Importance of Functional Morphology for Fishery Conservation and Management: Applications to Hawaiian Amphidromous Fishes

The functional capabilities of species can have a strong effect on their ability to maintain sustainable populations in anthropogenically altered environments. This is especially true among species comprising freshwater ichthyofaunas on small oceanic islands, where fishes frequently traverse boundaries between different ecosystems. Many aspects of functional performance in fishes relate directly to morphological features and limitations. In this review, we use the ichthyofauna of the Hawaiian Islands as an example to demonstrate how the habits, habitat, and in-stream distribution of five amphidromous fish species relate to the functional morphology of locomotion and feeding. Furthermore, we evaluate how performance limitations related to functional morphology might affect each species under changing environmental conditions. Based on this analysis we make four key recommendations. (1) Hawaiian stream management plans need to be tailored to island-specific conditions. (2) Estuaries need to be studied as a critical habitat because of the interface between fishes and human populations in these areas. (3) New recruits of Sicyopterus stimpsoni might serve as a key indicator species to monitor long-term health of Hawaiian estuaries. (4) The broad use of the Index of Biological Integrity (IBI) to assess Hawaiian stream health needs to be critically evaluated.