- A study found that on the most populated island in American Samoa, traditional village-based protections and remote sites had the highest density of giant clams — outperforming federally designated no-take zones in one case.
- The authors suggest that traditional community stewardship could offer a viable alternative to federal restrictions, especially in areas communities rely on for giant clam harvesting, while respecting traditional management practices.
- The giant clams, which are slow-growing, face threats from habitat degradation, ocean warming, watershed pollution and overharvesting.
- The NOAA National Fisheries Service proposed protections for several giant clam species in 2024 which could lead to a top-down ban on harvesting. Some sources say a blanket ban without including communities in conservation strategies would impact people who rely on harvesting.
For coastal Indigenous communities in American Samoa, giant clams are deeply rooted in fa‘a Sāmoa (the Samoan way of life) and local food systems.
According to the findings of a study published in PeerJ, it is village-based protections like fa‘asao (fishery closures) that have helped conserve giant clams lying in the islands’ shallow water coral reefs. The authors found that the highest clam densities and species are located in remote sites and areas under traditional village enforcement, outperforming federally designated no-take zones on the most populated island.
The authors examined giant clam population trends, clam densities and distributions, and species composition across six islands — Tutuila, Aunuʻu, Ofu, Olosega, Taʻū and Muliāva — from 1994/5 to surveys conducted between 2022-24. While the highly populated island of Tutuila had the lowest clam densities with 83.5 individuals per hectare (33.8 per acre), remote islands like Taʻū and Muliāva showed higher densities up to 812 to 1,166 per hectare (328 to 471 per acre).
On Tutuila, which had multiple types of management zones, subsistence and remote sites had the highest densities of giant clams, followed by remote areas, then village protected areas. Federal no-take sites held the lowest mean density of clams overall on the island.
“By restoring local stewardship, cultural accountability, and respect for customary marine tenure values, community-led systems like fa‘asao have strengthened marine ecosystem conservation through village-based fishery closures,” Dimary Ulberg, an Indigenous Samoan and program manager of the Community-based Fisheries Management Program (CBFMP) at the Department of Marine and Wildlife Resources (DMWR), said by email.
Empowering traditional community stewardship, the study suggested, can offer a viable alternative to federal restrictions — especially in areas communities rely on for clam harvesting — while respecting traditional management practices in American Samoa.
“Some of the results were surprising,” Paolo Marra-Biggs, the lead author of the study and a PhD candidate at the University of Hawaiʻi at Mānoa, told Mongabay by email.
“Despite the global decline of giant clams, we found that some areas in American Samoa [Tutuila, Taʻū and Muliāva] still supported strong populations, especially where harvest pressure was low or where communities actively managed their reefs,” he said.
The maxima clam (Tridacna maxima) had the most dominant population, while small populations of the fluted giant clam (T. squamosa) and Noah’s giant clam (T. noae) were primarily located in village-managed areas.
Behind the conservation scene
“Many island villages manage their own protected reef areas called fa‘asao, and we saw a strong effect of village stewardship on the conservation of giant clams,” Marra-Biggs said.
Certain nearshore waters are under the jurisdiction of Indigenous Samoan communities through CBFMP — a co-management approach between the village community and the DMWR to protect marine resources. Under the program, communities establish their own terms and commitment periods for fishery restrictions. Not all village-based management areas are under the CBFMP program, though.
Aligned with the customary marine tenure values guided by the Samoan governance, Ulberg said villages establish their own closure terms through consensus among matai (village chiefs) and community members.
“They set timelines, species, and fishing gear restrictions that help manage and rebuild fish stocks, habitats, and ecosystems over time while implementing the community’s local and traditional ecological knowledge,” she told Mongabay.
In terms of sustainable conservation impact, she argued that village-based protection can be more effective than federal no-take zones as compliance is culturally internalized, which help encourage long-term behavioral change.
“Village-based closures often reflect the community’s collective values, traditional leadership aligned with subsistence priorities and cultural values,” she told Mongabay. Compliance is thus aligned with culture, which helps encourage long-term behavioral change and community buy-in.
Pressures on clams
As giant clams are large, easy to collect, and have long been an important food source, areas near human populations have historically seen the most pressure from harvesting, said Marra-Biggs.
“Unlike the remote islands, Tutuila — where 98% of the residents live with access to roads, harbors, and fishing activity — face harvesting pressure,” he said.
Harvesting often targets the large-sized individuals that contribute the most eggs to the next generation. If too many of them are removed, the population can lose a large portion of its reproductive potential, the authors say.
“Large clams can produce far more eggs than smaller ones,” Marra-Biggs said. “The various species have differences in their growth rates, and age/size of maturity. However, reproductive output increases dramatically as these species get bigger.”
When it comes to conservation, Marra-Biggs said, the reproductive success of giant clams is heavily influenced by their size. For the most common species, such as the maxima clam, individuals generally reach reproductive maturity around 10 to 12 centimeters (3.9 to 4.7 inches) in shell length.
Chief fisheries biologist for the DMWR, Domingo Galgo Ochavillo, said that land-based pollution affecting watershed quality is also a growing risk for clam species, amid existing threats from ocean warming.
“Clams are like corals. When the pollution leads to increased turbidity from sedimentation, it blocks the sunlight that clams require for photosynthesis, hindering their growth.”
Many scientists also raise concerns about the potential impact of deep-sea mining off the coast of American Samoa on marine biodiversity. In January 2026, NOAA’s National Ocean Service announced a project to map critical mineral deposits in the region.
Forging a collaborative effort?
Given these multifaceted pressures, Ochavillo said, a partnership between communities and the government, aligned with community values and practices, is important not only for giant clams but also for sustainable marine conservation.
The village councils that comprise village chiefs have locally managed the resources for generations, he said.
“If they need to know the status of their coral reefs or how their resources are doing, the government steps in to provide grants or scientific and technical support,” he added.
Ulberg said integrating village bylaws into the CBFMP has expanded the enforcement capabilities of the DMWR. Community stewardship and management are currently recognized under the American Samoa Administrative Code Title 24 defining the fishing and community-based fisheries management (CBFM) regulations: Ulberg said these prioritize community conservation while implementing ancestral systems that are embedded in their cultures.
More can be done, according to the authors. They recommend community training and spatially distributed monitoring paired with community engagement as effective in ensuring long-term persistence of giant clam populations.
In 2024, the NOAA National Marine Fisheries Service proposed to list five clam species as endangered and one as threatened under the Endangered Species Act (ESA). Once finalized, it would lead to prohibitions on import and export while imposing bans on the local harvest of the six species.
A blanket ban on the giant clam harvest, sources said, can undermine community-based resource management that has existed for generations.
“The proposed listing is not really helping the community,” Ochavillo said. “If the species are finalized under ESA, communities say they can’t harvest them for food or earn money from having tourists visit their giant clam nurseries.”
One challenge with giant clams, Marra-Biggs told Mongabay, is that several species look very similar under water, complicating species identification.
“It wasn’t until recently that one species, Tridacna noae, had been discovered in American Samoa.”
Broad regulations in such cases could potentially restrict the harvest of species that are still relatively abundant locally, he said, emphasizing that the ESA could be a powerful conservation tool, but applying it in places with strong cultural fishing traditions can do more harm than good.
Sources emphasize the need for conservation approaches that work alongside local stewardship rather than replacing it.
“Conservation does not always need to start from scratch,” Marra-Biggs said. “In many cases, traditional management systems are already functioning well and supporting them with monitoring, research, and collaboration may be one of the most effective ways to sustain reef resources.”
Banner image: A maxima clam (Tridacna maxima) in American Samoa. Image by Paolo Marra-Biggs/UHM HIMB.
Rep from American Samoa calls for opening protected Pacific waters to tuna fishing
Citation:
Marra-Biggs, P., Brown, E. K., Ochavillo, D. G., Green, A. L., Lawrence, A., Tramonte, C., Vaeoso, V., Moffitt, I., Schnurle, K., Molina, N., & Toonen, R. J. (2025). Status and trends of giant clam populations demonstrate the effectiveness of village-based protection in American Sāmoa. PeerJ, 13, e20290. doi:10.7717/peerj.20290
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