Kiribati Giant Clam Fishery
The Kiribati giant clam multi-species subsistence fishery in the Gilbert Islands shows resilience in the ecological and socio-economic dimensions to marine heatwaves and ocean acidification where adaptive customary management was successfully implemented despite limited capacity from the national government. Ecologically, the species fished are generally resilient to climate change due to high plasticity, evolutionary potential, ecosystem connectivity, and larval dispersal. Additionally, there is high species diversity within the fishery (multi-species), which provides increased flexibility (e.g., differences in depth and spatial ranges, life history traits, and spawning seasons). However, overfishing, eutrophication, and pollution have pushed this fishery past the threshold of ecological resilience in the urbanized island of South Tarawa where the governance and socio-economic dimension have failed. Conversely, on remote outer islands, where the socio-economic dimension has shown promise in combating these anthropogenic influences, ecological resilience has been enhanced and the fishery has persisted despite the frequency and severity of climate-related impacts increasing. Thus, the resilience of the fishery moving forward will depend on the socio-economic dimension and all accountable actors. Specifically, maintaining and fostering the resilience mindset, learning capacity, place attachment, and agency while maintaining social capital. Wide-scale habitat degradation from coral bleaching coupled with the unknown physiological stressors of changes in sea surface temperature and ocean acidification has, and will continue to, impact the fishery. However, customary adaptive management through engaged local agents (Island Council; i.e., not national agents) has shown to be critical in the resilience of the fishery moving forward.
Four species of giant clam occur and are heavily targeted and fished for subsistence in the Gilbert Islands (by body size, large to small): Tridacna gigas, Hippopus hippopus, T. maxima, and T. squamosa. While T. gigas, the most endangered clam and largest living bivalve mollusk, is commonly known as the ‘giant clam’ all four species are giant clam species. The clams’ primary habitat is on structured coral reefs and back reefs in both the fore-reef and lagoon reef habitats. Giant clams represent a key function within the coral reef community. Their tissues are food for a wide array of predators and scavengers, while their discharges of live zooxanthellae, feces, and gametes are eaten by opportunistic feeders. They increase the topographical heterogeneity of the reef, act as reservoirs of zooxanthellae (Symbiodinium spp.), and also potentially counteract eutrophication via water filtering. The shells also provide substrate for commensal and ectoparasitic organisms (Neo et al. 2015). Despite this, limited monitoring has been conducted by the Kiribati Fisheries Division from the Ministry of Fisheries and Marine Resources Development (MFMRD).
Parallel to the functional role on coral reefs, giant clams represent a traditionally and culturally important food source for Kiribati. This contextual consideration is particularly for remote outer islands. The clams are used in traditional dances, served for special occasions, and play a critical role in food security as they are dried, salted, stored, and eaten if the household is unable to obtain seafood for other reasons (e.g., weather, boat issues). Thus, all species are heavily fished by free divers year-round, resulting in a general understanding that the fishery has been in decline since 2004 (Delisle et al. 2016). Further, in 2008 T. gigas was thought to be nearly locally extinct from the urbanized and overpopulated island of South Tarawa and the neighboring islands of North Tarawa and Abaiang (Awira et al. 2008; Preston 2008a, 2008b). Across all islands species body size has similarly declined. While small operators, aquaculture, and artisanal based fisheries operate (very short value chains), the majority of fishing pressure comes from subsistence fishers (Preston 2008a).
Resilience Attributes and Linkages
The response from the government’s national fishery branch, MFMRD, was the preparation of the Kiribati National Giant Clam Fishery Management Plan (FMP) in 2013, which followed the 2010 Fisheries Act and a large-scale coral bleaching event. The primary purpose of the giant clam FMP was to establish an effective and enforceable management structure for the Kiribati giant clam fishery. The main objective was to ensure the sustainable development, conservation, and management of the giant clam fishery and harvesting of giant clams. The 2013 FMP proposed T. gigas be banned from fishing, harvest restrictions for other giant clam species enacted, and increased reporting with an ongoing program for monitoring catch data and more scientific information. However, despite tangible action items for sustainable harvest, no national steps were made. Further, in South Tarawa, where governance operates at the island level due to not having distinct communities associated with a particular village, which has resulted in limited place attachment and agency paired with low accountability and social capital, the fishery continued to decline.
Island Councils (IC) represent the local level of governance on the remote outer Gilbert Islands in Kiribati. They act at the scale of a single village, allowing the IC to make adaptive decisions quickly. There is strong leadership and initiative through village elders, who have an interest in continuing the tradition of customary adaptive management, and ensuring a balance of ecological and social outcomes from the fishery (Campbell and Hanich, 2014). On outer islands where IC’s operate, decision-making is the result of a participatory, equitable and inclusive, and bottom-up approach. However, the high resilience mindset, learning capacity, place attachment, and agency from the fishers and general public on outer islands has resulted in the implementation and success of community-based fisheries management. Across different outer islands IC’s have independently implemented giant clam fishing quotas, permanent or rotational no take areas, and even banned the take of T. gigas.
Both South Tarawa and the outer Gilbert Islands have experienced system-wide shocks. Particularly, climate change has caused wide-scale habitat degradation following large-scale coral bleaching events. Severe coral bleaching can result in a high loss of coral cover, reduced structural complexity following coral mortality (a key habitat component of giant clams), and large-scale settlement of algae if a phase shift occurs (turf and macroalgae), which directly or indirectly, depending on severity, leads to reduced giant clam settlement and future recruitment if the population abundance is not stable. Coupled with the physiological stress from changes in sea surface temperature (symbiotic associations with photobionts) and ocean acidification (calcareous growth), threats to giant clams will continue to increase through the Anthropocene. However, recent studies have shown that giant clams, without additional anthropogenic pressure (overfishing, eutrophication, and pollution) are quite resilient to climate change through plastic and evolutionary responses associated with intact ecosystem connectivity and well-distributed larval dispersal when the population abundance and age structure is stable (Campbell and Hanich, 2014). For example, Morishima et al. (2019) found that under elevating temperature heat-resistant zooxanthella grew in clams and were passed to adjacent juveniles through photosynthetically active fecal pellets. However, overfishing, eutrophication, and pollution have pushed the giant clam fishery at South Tarawa past the threshold of ecological resilience.
Overfishing on remote outer islands has been mediated by customary closures, quotas, and species-specific regulations, which have acted as a buffer. On islands where the socio-economic dimension has shown promise in combating the aforementioned anthropogenic influences, ecological resilience has been enhanced and the fishery has persisted despite the frequency and severity of climate-related impacts increasing. Thus, while adaptive customary management is capable of implementing measures for resilience across all Gilbert Islands, maintaining and fostering the resilience mindset, learning capacity, place attachment, and agency at the local scale of each village has been the primary driver of resilience. Abaiang, despite giant clams nearly becoming locally extinct in 2008, stands as a flagship of resilience for the fishery. Through community-based fisheries management, specifically fisher-driven no take marine protected areas, Abiang today has a stable giant clam population and associated fishery despite the proximity to South Tarawa. Thus, maintaining the connections within the socio-ecological system will be key to overcoming climate-related impacts and increasing long-term resilience for other islands in the future. In summary, customary adaptive management through local actors, despite limited capacity from the national government, has enhanced the ecological resilience of the giant clam fishery in Kiribati.
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Delisle A, Namakin B, Uriam T, Campbell B and Hanich Q. 2016. Participatory diagnosis of coastal fisheries for North Tarawa and Butaritari island communities in the Republic of Kiribati. Penang, Malaysia: WorldFish. Program Report: 2016-24
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Acknowledgments: We would like to thank Aranteiti Tekiau, Katherine L. Seto, Erietera Aram, Toaea Beiateuea, Christopher D. Golden, Bwebwenikai Rabwere, Rateiti Vaimalie, and Douglas J. McCauley.
Photo copyright Jacob Eurich 2022