Fishing-induced groupers stock dynamics in Karimunjawa National Park, Indonesia

As a result of high levels of exploitation, in many regions of the world grouper (Epinephelidae) populations are at risk and/or declining steadily, such as in Indonesia. The aim of this study was to determine grouper stock sizes in Karimunjawa National Park, Indonesia. If the establishment of the park with no-take zones was effective in protecting grouper populations, the biomass of the grouper populations in this park should have increased or at least have been maintained between 2005 and 2012, the period under study. We found that grouper mean abundance declined between 2005 and 2012, with a fluctuating mean biomass, but that the mean biomass increased from 2009 to 2012. A significant difference was found in the abundance and biomass of groupers between the different core zones, but no significant difference was observed for three observed species between these zones. Three fishing gear types are used by fishermen to catch groupers, with speargun fisheries being the most effective. In 2011, the speargun effort was decreased, based on self-regulation by fishermen; this resulted in a change in the groupers’ target size and impacted recruitment success, with an increase in the stock size and biomass of groupers in 2012. Based on our analysis, we conclude that the establishment of marine protected areas alone, as exemplified by the establishment of three core zones in Karimunjawa National Park, is not sufficient on its own to protect natural populations of groupers, and that fishing-gear regulation and community support are also required.