Linking the biology and ecology of key herbivorous unicornfish to fisheries management in the Pacific

Naso lituratus (orangespine unicornfish) and Naso unicornis (bluespine unicornfish) are widespread species that are heavily targeted in many nearshore fisheries of Pacific Island countries. In addition to providing a critical food and income source, both species fulfil critical ecological functions in the top-down control of coral reef macroalgae; particularly fleshy brown algae (i.e. Sargassum spp.) which can out-compete and smother corals. Despite heavy long-term harvesting, there are currently very limited species-specific management measures. This review assesses the biology and ecology of both species, and combines this with the current status of the fisheries in the Pacific, and proposes realistic ecosystem-based species-specific fisheries policies. Although unicornfish populations have displayed continuing resilience to heavy fishing pressure, reports of declining stocks combined with a range of life-history traits (i.e. longevity, habitat-specificity, easily targeted aggregations), indicate that both species are vulnerable to overexploitation. Modern day common fishing practices such as scuba and night-time spearfishing are intensifying their exploitation. The most effective management measure would be fishing effort constraints, including banning modern and unsustainable methods. However, owing to enforcement limitations in Pacific Islands, the most practical approach to management would include a combination of management tools, including periodic sales bans around identified spawning times (i.e. Hawaii; May–June), and size/catch limits. Furthermore, home range data suggest that even with limited knowledge, small MPAs (<1 km²) in structurally complex areas using natural boundaries should accommodate the movement patterns of both species and provide sufficient protection; although MPAs of > 10 km linear distance are recommended for N. lituratus. This comprehensive review confirms the pressing need for implementation of the aforementioned management practices to protect these species in regions where they are heavily targeted, and prevent the impairment of their critical ecological function and importance as a food and income source.