Herbivorous fish rise as a destructive fishing practice falls in an Indonesian marine national park

Abstract

Securing ecosystem functions is challenging, yet common priority in conservation efforts. While marine parks aim to meet this challenge by regulating fishing through zoning plans, their effectiveness hinges on compliance levels and may respond to changes in fishing practices. Here we use a speciose assemblage of nominally herbivorous reef fish in Karimunjawa National Park (zoned since 1989) to investigate whether areas subject to a restrictive management regime sustained higher biomass over seven years compared to areas where moderate and permissive regulations apply. Using a trait-based approach we characterize the functional space of the entire species pool and ask whether changes in biomass translate into changes in functional structure. We track changes in predator biomass, benthic community structure, and fishing practices that could influence herbivore trajectories. Overall herbivore biomass doubled in 2012 compared to 2006-2009 and remained high in 2013 across all management regimes. We found no evidence that this biomass build-up resulted from predator depletion or increased food availability but suggest it emerged in response to a park-wide cessation of fishing with large drive nets known as muroami. The biomass increase was accompanied by a modest increase in taxonomic richness and a slight decrease in community-scale rarity that did not alter functional redundancy levels. Subtle changes in both functional specialization and identity of assemblages emerged as generalist species with low intrinsic vulnerability to fishing recovered sooner than more vulnerable specialists. While this implies a recovery of mechanisms responsible for the grazing of algal turfs and detritus, restoring other facets of herbivory (e.g., macroalgal consumption) may require more time. An increase in the cost-benefit ratio per journey of muroami fishing facilitated a ban on muroami nets that met minimal resistance. Similar windows of opportunity may emerge elsewhere in which gear-based regulations can supplement zoning plans, especially when compliance is low. This does not advocate for implementing such regulations once a fishery has become unprofitable. Rather, it underlines their importance for breaking the cycle of resource depletion and low compliance to zoning, thus alleviating the resulting threats to food security and ecosystem integrity.

Fishing restrictions and remoteness deliver conservation outcomes for Indonesia's coral reef fisheries

“…For these fish, even when nonselective gears (e.g., nets, traps) are banned, more targeted controls on selective gears (e.g., spearguns) are also required especially in areas that are moderate to highly populated by people (Campbell et al., ; Cinner et al., ). For Indonesia, this finding implies that if MPAs are to elevate total biomass and ecosystem functioning above the levels of gear‐based management (McClanahan, Maina, Graham, & Jones, ), permanent closures require: (1) strengthening of customary or local co‐management institutions (Cinner et al., ), (2) stronger community compliance than has been shown to date (Bejarano, Pardede, Campbell, Hoey, & Ferse, ), (3) a demonstration that they confer equitable benefits to strengthen legitimacy and compliance (Glaser, Breckwoldt, Deswandi, Radjawali, & Ferse, ), and (4) be of sufficient size to protect home ranges of roaming fishery targets like piscivores (Green et al., ).…”

Coral Reef Community Changes in Karimunjawa National Park, Indonesia: Assessing the Efficacy of Management in the Face of Local and Global Stressors

“…Since its establishment in 1985, management of Karimunjawa National Park has evolved in response to changing threats and feedback from scientific monitoring, as well as changing local and national government policy, and input from the community of 9000 people that live and work in the archipelago [18,23]. Management reviews have led to the park being rezoned twice.…”

“…Fishing pressure on Karimunjawa's reefs has traditionally been intense [15,23]. Seventy-percent of the community are involved in artisanal fishing [24], but the relative proximity of the island group to Java Island, home to more than 60% of the population of Indonesia, also poses a challenge for reef managers [21].…”

“…The archipelago continues to be the most important artisanal fishing area in Java Sea region [26] for peri-reefal pelagic fish (70% of the local catch) and reef fish (30%) [21,22]. While the population of Karimunjawa has been stable for over a decade [22], fishing pressure has changed across the park over time [23]. Harmful fishing practices, including cyanide fishing, the use of explosives and poisons, use of rocks for anchors by the fishing community [27] and muro-ami were once widespread and practised indiscriminately (except in Core Zones [18]).…”

“…Muro-ami was outlawed since June 2011 in Karimunjawa, and more widely across Indonesia in 2015 [28], although some illegal fishing was still occurring in the northwest sector of the park at the time of the study. Reductions in harmful fishing activities have led to an increase in fish biomass, including herbivorous fish (important in maintaining reef health) across the park [23].…”