Marine Biogeographic Assessment of the Main Hawaiian Islands

The state of Hawai‘i is working to develop local renewable energy sources to reduce its dependence on fossil fuels. Most of the State’s potential renewable energy resources (notably, wind) are located in federal waters from 3 to 200 nm offshore. The Bureau of Ocean Energy Management (BOEM) regulates the leasing, construction and operation of most renewable energy projects in federal waters, and is required to evaluate potential human, coastal and marine impacts from these projects. BOEM partnered with the National Oceanic and Atmospheric Administration’s (NOAA) National Centers for Coastal Ocean Science (NCCOS) to gather biogeographic information in support of this evaluation around the Main Hawaiian Islands (MHI). The complexity of products from this assessment range from simple animal distribution maps to mathematical models depicting the predicted distributions of animals. Biogeographic analyses and data products were specifically tailored to meet BOEM’s needs, and designed to fit within BOEM’s framework of offshore lease blocks.

This biogeographic assessment addresses three main questions: (1) how are select species or taxonomic groups distributed spatially and temporally around the MHI?; (2) what environmental conditions influence these distributions?; and (3) what significant gaps exist in our knowledge about the biogeography of the area? To answer these questions, existing, readily-available spatial information was compiled and synthesized, including information on the physical and biological environment, benthic habitats, fishes, sea turtles, marine mammals and seabirds. The assessment focused on federal waters and taxa that were: (1) more likely to interact with renewable energy infrastructure, (2) culturally significant, (3) legally protected, and/or (4) economically valuable. Collaborations with local managers, scientists, and experts from a variety of federal, state, academic and non-governmental organizations were crucial. These partners contributed their data, time and expertise, and many were contributing coauthors on this report.

The assessment includes two main components: (1) a technical report (this document) and (2) associated spatial datasets for use within Geographic Information System (GIS) software. Many of the spatial datasets presented here are publicly available from NOAA’s National Centers for Coastal Ocean Science (https://coastalscience.noaa.gov/projects/detail?key=163) and from NOAA’s National Centers for Environmental Information (NCEI Accession 0155189; https://data.nodc.noaa.gov/cgi-bin/iso?id=gov.noaa.nodc:0155189). These maps, databases, and analyses are one component of the larger BOEM and State processes to evaluate offshore renewable energy proposals around the MHI. They were not designed to replace any further analysis required by law. For more information about how these products may be used, please contact BOEM’s Pacific OCS Region: https://www.boem.gov/Pacific-Region/. This report is organized thematically, and is comprised of seven chapters and supporting appendices. The main objective, basic approach, and important findings from each chapter are as follows:

Chapter 1: Introduction

• The state of Hawai‘i would like to develop local renewable energy sources (notably, wind). Much of the State’s potential wind energy is located in federal waters. BOEM regulates most renewable energy projects in federal waters, and is required to assess the potential environmental impacts of these projects during the leasing process.
• To help inform this process, NOAA’s NCCOS characterized the marine biogeography and identified key data gaps around the MHI. This project is a small piece of a much larger BOEM leasing process.

Chapter 2: Environmental Setting

• Atmospheric and oceanographic patterns were mapped using satellite imagery and oceanographic models. These maps were used to describe the regional environment, and to develop models predicting deep-coral, cetacean, and seabird distributions.
• Seasons around the MHI are driven by changes in the North Pacific Subtropical High and the Aleutian Low. Winter (November to April) is cooler, rainier, and dominated by the North Pacific swell. Summer (May to October) is warmer, less rainy, and dominated by the northeasterly trade winds and swell.
• Mountains and submerged topography change the direction and speed of winds and currents. These interactions cause the leeward sides of the island to be warmer and drier, and create frequent convergence, mixing, upwelling, fronts and eddies in the channels between the islands (e.g., the Kaiwi, Pailolo and ʻAlenuihānā Channels), and on the leeward sides of the islands (e.g., Kona Coast, Hawaiʻi).

Chapter 3: Benthic Habitats and Corals

• Seafloor habitats were characterized within shallow (150 m) areas using existing maps, in situ survey data and spatial models.
• In shallow areas, rock/boulder habitats were less dominant, hard coral cover declined and algal cover increased moving from the southeast to the northwest. Hard coral cover was generally higher on leeward sides (e.g., Kona Coast, Hawaiʻi) and more sheltered areas (e.g., Kāneʻohe Bay, Oʻahu) around the islands.
• In mesophotic areas, information was limited to the ‘Auʻau Channel. Predicted probabilities of occurrence were highest for three genera of hard corals along the western Maui coast.
• In deep areas, the distribution of observed deep-coral presences and predicted suitable habitats varied among 18 taxonomic groups, but were often concentrated nearby specific locations, such as Cross Seamount, Makapuʻu Point, Makalawena Bank, Lō‘ihi Seamount and the southern edge of Penguin Bank.

Chapter 4: Fishes

• The distribution of commercially important bottom fishes (i.e., the deep seven) was mapped using fisheries dependent and independent data. Predictive models were developed describing the spatial distribution of reef fishes (i.e., species richness and biomass, endemic species richness and biomass, and biomass of resource fishes).
• For bottom fishes, the fishery is most active in the winter months. Datasets identified Southern Penguin Bank, Maui Nui channels, west Hawaiʻi, southern Maui, and northern Moloka‘i as important areas.
• For reef fishes, the highest biomass and richness values were in areas least accessible to humans such as the Hamakua and Puna districts on Hawaiʻi, northern Moloka‘i, eastern Maui, and western and southeastern Oʻahu. Conversely, areas more accessible to humans had overall lower richness and biomass values and included the Kona Coast, Hawaiʻi, west Maui and southern Oʻahu.

Chapter 5: Sea Turtles

• Basking, nesting, and stranding locations were mapped (in the context of human populations, shoreline cliffs, and beaches) for the five species of sea turtles using in situ sightings data. All five species are protected under the Endangered Species Act (ESA). Green turtles (Chelonia mydas), the most abundant species, were reported basking at 62 locations, with a majority of reports from northwest O‘ahu and west Hawai‘i.
• Most nesting reports are for green turtles with the majority occurring on Kaua‘i and Maui. Hawksbill (Eretmochelys imbricata) have key nesting sites on southern Hawai‘i.
• Stranding reports are mostly for green turtles, with many from O‘ahu and parts of Maui. Fibropapillomatosis is the major cause along most coastlines. Other common causes include entanglement along northeast Kaua‘i and southwest O‘ahu, and illnesses, boat impacts and predation along the Kona Coast, Hawai‘i.

Chapter 6: Marine Mammals

• The distributions of cetaceans (15 species) were mapped using in situ sightings data. Seasonal relative abundance predictions were created for seven of these species. Terrestrial and at-sea locations of the endangered Hawaiian monk seal (Neomonachus schauinslandi) were also mapped using in situ sightings and telemetry data.
• For cetaceans, species distributions were variable, although some species were sighted or predicted to be consistently closer to shore (e.g., Humpback whale, Spinner dolphin, Common bottlenose dolphin), while other species were generally located further offshore (e.g., Rough-toothed dolphin, Sperm whale). Several species were sighted along the Kona Coast, Hawaiʻi, including Cuvier’s beaked whale, Dwarf sperm whale, Pygmy killer whale, Pantropical spotted dolphin, and Short-finned pilot whale.
• Critical habitat for Hawaiian monk seals includes 0-10 m above the seafloor from 200 m depths to the shoreline, then from the shoreline extending 5 m inland. Hawaiian monk seals were sighted around each of the MHI, although more haul-out sites were identified on the islands to the northwest. Ni‘ihau, Kaua‘i and O‘ahu were also frequented by tagged seals, along with Penguin Bank, the east side of Lāna‘i and Kahului Harbor, Maui.

Chapter 7: Seabirds

• The distributions of seabirds (24 species) were mapped using in situ data. Seasonal relative density predictions were created for 14 of these species, and maps of maximum potential foraging areas were created for seven species.
• Species distributions were variable, although several species were sighted or predicted to be offshore of the Kona Coast, Hawaiʻi (e.g., Sooty Tern, Wedge-tailed Shearwater, Juan Fernandez Petrel, Black-winged Petrel, and Bulwer’s Petrel).
• Breeding species were generally located closer to land (e.g., Black Noddy, Brown Noddy, and Brown Booby) or occurred more evenly throughout the study area (e.g., Sooty Tern and Wedge-tailed Shearwater). Non-breeding/migratory species tended to be further offshore with some species being restricted to specific parts of the study area (e.g., Juan Fernandez Petrel and Mottled Petrel in the southeast).

The biogeography of the MHI is shaped by atmospheric and oceanographic conditions that operate at different temporal and spatial scales around the islands. Marine animals respond to these changing conditions in different ways. Some taxonomic groups and species use the same locations year round (e.g., on Penguin Bank or offshore of the Kona Coast, Hawaiʻi), while most taxa utilize different geographic areas at different times of the year. Understanding these spatial and temporal patterns is critical for marine spatial planning efforts, including offshore renewable energy development. For some taxa, this marine biogeographic assessment marks the first time that their space-use patterns were mapped or modeled in the MHI, and the associated data compilation made available online. It establishes a baseline for assessing potential impacts, a guide for monitoring change, a roadmap for prioritizing how to fill data gaps, and a framework for integrating ocean research and management efforts moving forward.