Determining Reef Fish Abundance in Marine Protected Areas in the Northern Mariana Islands

Michael Trianni

Department of Lands and Natural Resources, SAIPAN

Theme: TH3

Marine Protected Areas (MPAs) in the Commonwealth of the Northern Mariana Islands (CNMI) are a relatively new concept. The primary purpose of CNMI MPAs is to enhance fish resources by protecting sections of the reef to serve as brood-stock and to provide fish 'spill-over' into adjacent areas. The measure of the early success of MPAs hinges partly on the ability to measure fish abundance using applicable statistical estimation methods. A stratified sampling approach was used to estimate reef fish abundances in two CNMI MPAs on an annual or biannual basis. The Sasanhaya Bay Fish Reserve in Rota was surveyed annually over a three-year period, while the Managaha Marine Conservation Area (MMCA) in Saipan was estimated biannually over a two-year period. Stratifications were based on qualitative habitat characteristics or depth contour. The precision of the sampling methodology was evaluated for varying levels of sampling effort by computer simulations of sampled data sets. Multiple versus single fish counter effects were evaluated by assessment of sampling variance for the MMCA. The ability to generate reliable estimates of fish abundance requires consistency in the fish counter, as well as reasonable identification of statistical strata. Providing a standardized, repeatable sampling scheme is essential to evaluating the success of MPAs over the long-term.