Fisheries yields and species declines in coral reefs

Abstract

Negative trade-offs between food production and biodiversity and the positive functional diversity - productivity relationships are potentially conflicting paradigms that are frequently evoked in conservation and sustainability science and management. While the complementary niches of species could potentially increase fisheries yields, stark food-diversity trade-offs have been proposed for wild-caught fisheries. Nevertheless, this first evaluation of stock biomass, yields, and species relationships in 115 coral reef locations in the Western Indian Ocean found that management for multispecies-maximum sustained yield (MMSY) will increase both food production and numbers of species relative to open access fisheries. A precipitous loss of >50% of species did not occur until >70% of the fishable and target biomasses was depleted. At MMSY, 6-15% of total predicted number of fish species were lost indicating a need for other conservation mechanisms. These patterns occurred because the best-fit to the yield-numbers of species relationship was either a saturation or convex parabolic relationship. Fishing at MMSY in coral reefs should provide considerable diversity required to support many ecosystem services. Low biomass and overfishing were common and around 80% of studied locations were losing ~2.0-2.5 tons.km-2.y -1 and 15-40% of their species relative to MMSY.

Low optimal fisheries yield creates challenges for sustainability in a climate refugia

“…The low production findings contrast with previous production estimates using a similar space‐for‐time substitution method and more widely distributed WIO data from more fisheries closures. The study concluded that fishable and target fish production in the WIO province had an r of ~0.23 (McClanahan, 2022). Many reef closures in the broadscale compilation were in more ocean‐exposed environments compared to reefs leeward of the large Pemba and Zanzibar islands in this more site restricted compilation.…”

“…Large-scale studies suggest a series of ecological thresholds associated with fish biomass that will have consequences for ecological processes, such as fisheries production and reef growth (McClanahan, Graham, et al, 2011). Thresholds vary along fisheries production gradients but many including biodiversity are supported at or just above maximum sustained yield (MSY) fisheries levels (McClanahan, 2018a(McClanahan, , 2022. What is less understood is the variability in fisheries production rates and the differences between existing and optimal catch rates.…”

“…Along the African coastline, this often entails reducing fishing pressure to promote stock recovery (McClanahan & Muthiga, 2016; Rehren et al, 2020; Robertson et al, 2018). Stock biomass is closely associated with the biodiversity of fish and other ecological resilience characteristics of fish communities (Graham et al, 2017; McClanahan, 2022; Zamborain‐Mason et al, 2023). Large‐scale studies suggest a series of ecological thresholds associated with fish biomass that will have consequences for ecological processes, such as fisheries production and reef growth (McClanahan, Graham, et al, 2011).…”

“…A minimum goal for reef climate refugia should be to avoid overfishing. This is expected to sustain and balance the human needs for fish while supporting ecosystem properties and processes (McClanahan, 2022). A better understanding of the stocks, production, and yield potentials is therefore an important step for planning and management in refugia.…”

Accounting for local categorizations and classifications of fish: Towards a food-centred governance of small-scale fisheries in coastal Kenya

“…However, their management is complex due to its characteristics of multiple gears, multi-species, many resource users, seasonality, and presence of migrant shers, thus rendering traditional sheries management hard to implement or ineffective (Munga et al, 2014). These complexities are related to the challenges that local management presents around the use of illegal gear, increasing number of shers and increasing demand for sh which compromise conservation efforts (Galligan et al, 2022;Mangi et al, 2007;McClanahan, 2022).…”