Culturally Important Fishponds in Hawaii

USGS Cooperative Research Unit Corner

Culturally Important Fishponds in Hawaii

Traditional Hawaiian fishponds, i.e., loko i’a, were culturally important resources for native Hawaiians that were an essential component of a sophisticated, integrated food production system. Native Hawaiians strategically placed stone walls along the coast to slow the mixing of relatively nutrient-rich surface water or ground water with sea water, essentially creating estuaries. Larval fishes were attracted to the habitats within the pond and entered the fishpond through a gated sluiceway only to find themselves trapped within the pond as they grew. Researchers at the Hawai’i Cooperative Fishery Research Unit (HCFRU), working in collaboration with the Hawai’i Division of Aquatic Resources, Kamehameha Schools, and the Edith Kanaka’ole Foundation, investigated how the species composition of fish assemblages in actively managed and inactive fishponds differed from those of a natural estuary and evaluated the demographic processes of important game species within fishponds.

Research being conducted in Hawaiin fishpond

Prior to European contact in 1778, it is estimated that more than 450 ponds were managed throughout the Hawaiian Islands that produced large quantities of fishes and other resources. However, changing demographics and systems of land ownership in Hawai’i after European contact resulted in a decline in the use and upkeep of fishponds, to the extent that only 38 fishponds remain in use today. However, the walls of most of the abandoned or inactive fishponds remain standing, allowing the fishponds to contribute to the productivity of the nearshore environment. Hawai’i has a limited amount of natural estuarine habitat relative to the amount of shoreline, making fishponds potentially important nursery habitats for native species.

Hawaiian fishponds are culturally important and viewed as a potential solution to enhance the food security of local communities in Hawai’i. Therefore, there are currently numerous grassroots efforts to restore fishponds to some capacity of production. However, these restoration efforts could alter the availability of nursery habitat for fishes and may need to be factored into the management of the nearshore fisheries. Researchers with the HCFRU and its partners conducted a spatially and temporally replicated mark-recapture study in a complex of three fishponds that connected to the same embayment of Hilo Bay on the windward coast of the island of Hawaii. The ponds differed in their degree of connectivity to the bay and the amount of freshwater inflow.

Differences in species assemblage were driven primarily by salinity and availability of hard-bottomed habitat. The sites with the lowest salinities and a large proportion of mud substrates were the lowest in species richness and dominated by non-native species. However, the survival of the highly desirable and native striped mullet, or ‘Ama’ama, Mugil cephalus, was higher in these low salinity, muddy substrate sites. Other native species reared in the fishponds, such as native kuhliid flagtails, or ʻāholehole, and yellowstripe goatfish, or Weke’a, Mulloidichthys flavolineatus, exhibited higher survival in sites with higher salinities or a higher proportion of rocky substrates. This trend in salinity was strongly and inversely correlated with distance from the makahā, or gated sluiceways connecting the fishponds to the ocean. Additionally, the number of connections to the ocean and the distance from them was associated with increasing prevalence of muddy substrates. Higher salinity sites had the highest species richness, likely due to proximity to and connectivity with the marine environment, allowing more native nearshore species, in particular juvenile reef fishes, to access and persist at these sites. Perhaps most interestingly, movement of fishes between fishponds and between the fishponds and the natural estuary of Hilo Bay was observed in both native and non-native species.

On the landscape scale, abandoned or unmanaged ponds are functioning as estuaries that are used by a diverse assemblage of native and non-native fish species. Depending on the degree of connection to the marine environment, Hawaiian fishponds may be providing a substantial number of recruits to populations of targeted, nearshore species and as more fishponds are restored and makahā closed, fisheries managers may need to adjust management strategies for wild populations.

While this loss of nursery habitat may pose a new challenge to fisheries management in Hawai’i, managed fishponds are likely to create conditions that are less conducive to the establishment and maintenance of populations of non-native and potentially invasive species. Hawaiian fishponds have withstood the test of time and continue to serve the communities of the islands. An increased understanding of their internal ecology and their role in the nearshore ecosystem will allow for a more comprehensive strategy for sustainable fisheries and resilient communities.

The ONB features articles from U.S. Geological Survey Cooperative Fish and Wildlife Research Units across the country. The Units are leading exciting, new fish and wildlife research projects that we believe our readers will appreciate reading about. This story was written by Ricky Tabandera,, Hawaii Cooperative Fishery Research Unit, MS student in the Tropical Conservation Biology and Environmental Science program at University of Hawaii-Hilo.

Photo Credit
Hawai'i Cooperative Fishery Research Unit
December 15, 2020