Second Kona Integrated Ecosystem Assessment Survey Completed

August 9, 2013

The second Kona Integrated Ecosystem Assessment (IEA) survey was completed in mid-June aboard the NOAA Ship Oscar Elton Sette. This research expedition built on the 2011 Kona IEA survey and involved scientists from NOAA's Pacific Islands Fisheries Science Center, the University of Hawaii's Joint Institute for Marine and Atmospheric Research, the University of Hawaii at Manoa and Hilo, NOAA's Hawaiian Islands Humpback Whale National Marine Sanctuary, and Duke University. And, in keeping with the goal of supporting students and educators, eight graduate and two undergraduate students and a NOAA Teacher at Sea participated in the survey.

This year's survey sampled physical and biological characteristics of the ecosystem at six selected locations (stations) off Kona and along seven transects between these stations. As in 2011, sampling methods included use of active acoustics (sonar), mid-water net trawls, and conductivity-temperature-depth (CTD) casts down through the water column. Active acoustics are used to determine the depth and density of high sonic scattering layers, which are composed of small fish, squid, and crustaceans that larger species in the ecosystem prey upon. Nightly mid-water trawls targeted the sonic scattering layer and identification of organisms in the trawl catch will help us interpret the active acoustic data, as well as provide information on relationships between different components of the ecosystem (population connectivity). CTD casts gather physical and biological oceanographic data, such as temperature, salinity, dissolved oxygen, and chlorophyll concentration. These data provide details on Kona's physical environment and on the abundance and composition of the phytoplankton community which provides energy to all higher trophic level species.

In addition to replicating some aspects of the 2011 survey, this year's survey also gathered information to create cetacean habitat models for the Kona region. Habitat areas were determined using information from both visual sighting of cetaceans and detection of cetaceans through their vocalizations (using passive acoustics). In addition, active acoustics and the oceanographic sampling mentioned above were used to determine key characteristics of habitat areas. The trawl catch details will also be used to help further our understanding of the cetaceans' forage. Finally, a University of Hawaii imaging sonar was deployed through sonic scattering layers to gather high-resolution data on the density of these layers. The density data will provide additional information on cetaceans' forage base and help us interpret the active acoustic data.

Combining the data collected on this year's Kona IEA survey gives us a snapshot of the entire Kona ecosystem, from the physical environment to the base of the marine food web to the top predators. While the synthesis of these data is only beginning, a few insights are already apparent. The figure below shows both temperature and chlorophyll data collected during the survey transects. These data indicate that there is a shoaling and intensification of the deep chlorophyll maximum at both the offshore and inshore northern stations compared to the southern and central stations. Further the observations of cetacean vocalizations, indicated by black dots in the figure, are most abundant inshore and along the southern transect.

Combining the information gathered on this year's survey with data collected in 2011 will provide further insight into important features of Kona's ecosystem. We expect that the next Kona IEA survey will be conducted in the summer of 2015.

Some preliminary results of the survey. Left: Data on temperature and chlorophyll were collected along both offshore and nearshore transects from CTD casts conducted at each of the six sampling stations. Right: Trawl catch composition, with circles scaled by total catch volume and segments of the circles representing the volume of each major group of organisms. Volumes were computed from the average catch results of two nightly tows, except at two of the east stations (central and northwest), where one nightly tow at each station was compromised by cookie cutter shark bites to the cod end of the trawl. Black dots indicate where cetacean vocalizations were recorded. The dashed lines indicate transects completed between stations.
Some preliminary results of the survey. Left: Data on temperature and chlorophyll were collected along both offshore and nearshore transects from CTD casts conducted at each of the six sampling stations. Right: Trawl catch composition, with circles scaled by total catch volume and segments of the circles representing the volume of each major group of organisms. Volumes were computed from the average catch results of two nightly tows, except at two of the east stations (central and northwest), where one nightly tow at each station was compromised by cookie cutter shark bites to the cod end of the trawl. Black dots indicate where cetacean vocalizations were recorded. The dashed lines indicate transects completed between stations.