Assessing the Oceanographic Conditions and Distribution of Reef Fish Assemblages Throughout the Gal?pagos Islands Using Underwater Visual Survey Methods

The Gal?pagos Islands are one of the most diverse marine ecosystems in the world because they lie at the confluence of several ocean currents in the eastern tropical Pacific Ocean (ETP). The Gal?pagos Marine Reserve (GMR) is a 138,000 km^2 area surrounding the archipelago that is divided into several zones based on the dispersal of fauna and marine resources. The goal of this thesis was to assess the distribution and abundance of reef fish assemblages throughout the GMR and to contribute to the existing knowledge of these assemblages. This project was performed during three visits to Gal?pagos: 16-30 May 2013, 16-19 November 2013, and 12-24 July 2014. Reef fish assemblage composition throughout the GMR was examined by collecting qualitative and semi-quantitative data using underwater visual survey techniques. Data on current and past oceanographic conditions around Gal?pagos were collected through in situ measurements and examining data collected by satellites.

Underwater surveys found a high species richness and wide range of trophic levels to exist across the Gal?pagos archipelago. Data were analyzed using several techniques including rank order of abundance (ROA), hierarchical cluster analysis, principal coordinates analysis, and regression. During 2013 surveys, 60 species from 32 families were recorded at 12 survey sites across the GMR. Through tests of similarity, it was found that fish assemblages across the GMR are not uniformly distributed and vary spatially. Ocean conditions such as temperature may influence fish assemblage composition at different islands. These results support previous studies that surveyed fish assemblages throughout the GMR and found that assemblages vary based on geographic location and that water temperature may play a role in how they are structured. In July 2014, data were collected around the northwest coast of Isla San Crist?bal at two sites previously surveyed in 2013. Fish assemblages around San Crist?bal showed little change from one year to the next in terms of species richness and diversity. Ocean temperatures were warmer and chlorophyll-a levels were lower in 2014 than in 2013, caused in part by El Ni?o climactic variations in the ETP during 2014. Information from this thesis may be used for a variety of applications including marine resource management and to support future zoning proposals in the GMR.