In addition to nutrient pollution from feed, other threats from aquaculture include risk of escape and genetic contamination of wild populations, disease, use of antibiotics and hormones, and attraction of animals. Two aquaculture map layers were developed for this project: ocean-based aquaculture and land-based aquaculture.
There have been two active Ocean-based aquaculture operations in the MHI. As of 2016, only one was in operation, offshore of Keahole Point on Hawai‘i Island, which grows Kahala (Seriola riviolana, marketed as Kona Kampachi) in an array of moored offshore net pens. The other operation, which grew Pacific Threadfin (Polydactylus sexfilis) off of Ewa Beach, O‘ahu, closed down in summer of 2012. It operated for 11 years, spanning much of the study period, and was therefore included in the dataset. For both operations, the footprint of the net pen array, dispersion fields for feed and feces, and “zone of mixing” designated by the DOH Clean Water Branch were digitized from environmental impact statements and monitoring reports. These were given arbitrarily decreasing values from 1 in the center to .1 at the edge of the zone of mixing.
Land-based aquaculture in the MHI consists primarily of shrimp ponds near the coastline, but also hatchery operations that stock offshore aquaculture and shrimp broodstock production. Footprints of terrestrial aquaculture operations were extracted from Hawai‘i State agricultural land use dataset (2015) and combined with footprints digitized using a list of aquaculture operations on the Hawai‘i Department of Agriculture website, Google searches, and identified using Google Earth and ESRI Imagery Basemap for visual validation. Aquaculture operation footprints were converted to raster with a value of one and decayed offshore using the same dispersion methods as the land based pollution layers.