Intense fishing pressure on Hawaii’s bottomfish during the last couple of decades has led to the depletion of deepwater snapper stocks around the main islands. The status of the onaga, Etelis coruscans, and the ehu, Etelis carbunculus is of particular concern to Hawaii’s fisheries managers since their spawning potential ratios have been well below the critical level for many years. Recently, the state implemented a recovery plan for these two species that includes the creation of 19 restricted fishing areas (RFAs) within the designated bottomfish essential fish habitat (EFH). However, since so little is known about deepwater habitats in Hawaii, the EFH is very broadly defined to be the band between 100 and 400 meters in depth around each of the islands. As such, both the EFH and the RFAs enclose substrates ranging from mud flats to basalt pinnacles, most of which, are unsuitable habitat for onaga and ehu. Therefore, what impact, if any, these RFAs will have on the stocks of these species, is unclear.

NURP is addressing this situation by supporting a project aimed at developing a more accurate EFH description for onaga, ehu, and other species of deepwater snappers in Hawaii. This project involves the use of the Pisces V submersible in conjunction with high-resolution multibeam sonar data and Arcview GIS to gain a better understanding of the geology and biology of their habitats. Six of the twelve dives for this project were conducted in 1998, with the remaining dives scheduled for the 2000 dive season. In order to differentiate important from unimportant features, researchers have chosen several different types of habitats around the island of Oahu to study . High-resolution multibeam sonar images were obtained from the U.S. Geological Survey (USGS) for each dive site. These images were imported into Arcview GIS and layered with the Pisces V tracking data to correlate the sonar data with the submersible observations (Fig.1). During the 1998 dives, both substrate characteristics and the sizes and numbers of invertebrate and fish species were recorded. Similar data will be taken during the 2000 dives, after which all of the data will be analyzed by Canoco statistical software, which is designed for community ecology applications.

Even though this work is still in progress, researchers believe they have already identified a number of important features of bottomfish EFHs. Onaga and ehu were observed in areas characterized by a hard carbonate, basalt, or mudstone substrate. On walls and pinnacles with sharp slopes, fish were observed only in areas of exposed rock. Furthermore, the porosity, rather than the lithology or rugosity of the rock, appeared to be the major factor determining suitability. This may be because the more holes and crevices on a site, the more potential prey species were found. Onaga and ehu are piscivorous and one particularly abundant species of small fish, Symphysanodon maunaloa was present wherever they were observed. Both onaga and ehu were absent over mud/sand substrates and hard exposed substrates with low porosity, as was S. maunaloa. Ehu were either solitary or in small groups that stayed close to the substrate. This species appeared to require shelter in the form of larger holes or crevices that they retreated to when the submersible approached. In contrast, onaga formed schools above the substrate and responded to the appearance of the submersible by simply swimming away. Since documenting the presence of these fish is an integral part of the project, bait stations were used to circumvent this avoidance behavior and assess the number and size of these fish at each study site (Fig. 2). In addition, bait stations provided the means to document important cryptic species of fish that would normally not be observed during submersible transects. Most notably among this group were conger eels (Conger oligoporous), moray eels (Gymnothorax berndti, G. nuttingi), and deepwater cods of the family Moridae (Fig. 3). Bait stations also attracted potential predators such as sharks) (Carcharhinus galapagensis, (Fig. 4) and kahalas (Seriola dumerilii).

Black corals (Cirripathes spiralis, Antipathes sp. ), hard corals (Dendrophyllids, Corallium sp.) and gorgonians were the most commonly observed attached invertebrates on these habitats (Fig. 5). Shrimp (Plesionika pacifica), galatheid crabs (Munida brucei), and starfish (Tamaria sp., Sphaeriodiscus ammophilus) were commonly observed epibenthic invertebrates. Other free-living invertebrates included decorator crabs (Paromala sp., Fig. 6), octopods, gastropods, , sea urchins (Stereocidaris sp., Actinocidaris sp.) and slipper lobsters (Scyllarides sp).

Once completed, this project will provide important data on the geological and biological characteristics of bottomfish EFH's. This information will be useful in refining both the EFH and RFA boundaries in Hawaii, which will hopefully lead to more effective management of the bottomfish fishery in the future.