Distribution and diet of four species of carcharhinid shark in the Hawaiian Islands: evidence for resource partitioning and competitive exclusion

Abstract

Competition and predation are both important in structuring the distribution of marine organisms; however, little is known about how competition and predation influence the distribution of elasmobranch fishes. We used data collected from shark control programs conducted between 1967 and 1980, throughout the Hawaiian island chain, to examine the distribution and dietary over- lap of the 4 most abundant carcharhinid sharks. Tiger sharks Galeorcerdo cuvier and Galapagos sharks Carcharhinus galapagensis were caught at all islands, but were more abundant in the north- western Hawaiian Islands (NWHI) than in the main Hawaiian Islands (MHI). Gray reef sharks Carcharhinus amblyrhynchos and sandbar sharks Carcharhinus plumbeus showed an inverse rela- tionship in distribution, with sandbar sharks abundant in the MHI, but virtually absent throughout the NWHI, and gray reef sharks only sporadically found throughout the MHI, but abundant in the NWHI. Dietary overlap was high between gray reef and sandbar sharks, and between sandbar and Galapagos sharks. Tiger sharks had low dietary overlap with all other species, except for large Gala- pagos sharks. The data analyzed in our study support the hypothesis that interspecific competition influences the distribution of carcharhinid sharks throughout the Hawaiian Archipelago.