POTENTIAL VALUE OF GEAR-BASED MANAGEMENT FOR CORAL REEF FISHERIES AND CONSERVATION

Abstract

Access to markets and globalization has fueled the expansion of fishing pressure in coral reef fisheries and has consequently led to overfishing on many reefs around the world. Overfishing has profound consequences for reef ecosystems and the people that rely on reef resources for nutrition and income. Collecting fisheries-dependent data required for traditional stock assessment methods that guide management is often infeasible for coral reefs due to the small-scale, dispersed, multi-species, and multi-gear nature of these fisheries. In addition, coral reefs are concentrated in developing countries that often have inadequate capacity for management and enforcement, which limits the effectiveness of the default management strategy for marine ecosystems around the world – marine protected areas. However, fishers on coral reefs use a variety of fishing gears and generally favor gear-restrictions over spatial closures. Thus, the aims of this dissertation were to investigate the effects of fishing pressure and habitat condition on reef fishes, quantify the selectivity of fishing gear types (i.e., hook-and-line, nets, and spears) for functional groups and size classes of reef fishes, and generate a fisheries model to observe population dynamics of reef fishes under various gear-restriction management scenarios. Chapter 1 is an overall introduction for the dissertation that provides background information for Chapters 2, 3, and 4. The general importance and scale of coral reef fisheries globally is outlined, and detailed information on fisheries-independent indicators (specifically size-spectra) and gear-restriction management are provided in this chapter. In Chapter 2, we investigate the effectiveness of a fisheries-independent indicator – size spectra slope – for detecting the effects of fishing and habitat condition on reef fishes. Size spectra slopes quantify the relationship between relative abundance and size of organisms. Size spectra can be useful for the assessment of coral reef fishes because fish life-history characteristics are related to fish size and, thus, can represent the flow and distribution of energy through food webs. We quantified benthic composition and size spectra of coral reef fishes using underwater visual surveys across three regions of Indonesia. We found that total fish biomass (proxy for fishing pressure) was the best predictor of size spectra for reefs fishes. Also, we found an interaction effect between fishing pressure and structural complexity such that structural complexity decreased as fishing pressure increased. Thus, suggesting that fishing pressure was associated with habitat degradation. Biomass and structural complexity were also the best predictors of size spectra slopes when carnivores and herbivores