Historic fishponds of Hawaiʻi: Spatial inventory and analysis of Loko Iʻa land cover change in coastal regions

Abstract

Rapid development over the last century drastically modified coastal landscapes in Hawaiʻi. As a result, many loko iʻa (Hawaiian fishponds) have been filled and developed or left in disrepair. Past studies and inventories have catalogued non-exhaustive lists, and today their results are undigitized and unconsolidated, making aggregated spatial assessments difficult. The objectives of this research were to quantify the approximate acreage of both extant and non-extant fishponds across the Hawaiian Islands and explore the utility of historic maps as basis for investigating land use and land cover (LULC) change of fishponds at a coastal case site. A comprehensive archival review of historic maps, surveys, aerial images, and literary sources was conducted to create a robust repository and map documented fishpond sites. Approximately 50 raster datasets were georectified and used to digitize the geographic boundaries of historic fishponds, whereas existing sites were mapped using high-resolution, high-accuracy satellite imagery. The resultant spatial data was used to evaluate comprehensive land cover comparisons and identify a study area to investigate localized LULC trends of nearshore fishponds using heterogeneous datasets. This effort substantiated a spatially-supported, quantifiable estimation of fishpond landcover change; revealing an approximate 30% decrease in total acreage of sites which had corresponding spatial components. Using the collation of spatial data generated, directed land cover investigations within a study vicinity at Pu’uloa, Oʻahu revealed a decrease from 43 fishponds (750 acres) as documented in 1873, to 4 fishponds (5 acres) at present-day. In addition, the data yielded a publicly available, comprehensive digital interactive map of over 300 fishponds. The outputs of this study are intended to support future research on assessment for restoration, bio yield capacity, and stewardship efforts.