Kona Coast Ecosystem Survey Focused on Cetacean Habitat, Marine Education, and More

June 12, 2013
The Kona IEA survey will be carried out along selected transects (dashed lines) and feature several key sampling stations (A-F).
The Kona IEA survey will be carried out along selected transects (dashed lines) and feature several key sampling stations (A-F).

On June 12, 2013, the NOAA Ship Oscar Elton Sette departed her home port at Ford Island, Pearl Harbor, for the second Kona Integrated Ecosystem Assessment (IEA) survey. This cruise, identified as SE-13-04, builds on the inaugural survey conducted in July 2011 and aims to further our understanding of the unique marine ecosystem along the Kona Coast of the island of Hawaii (Big Island). Participating in the expedition are scientists from NOAA's Pacific Islands Fisheries Science Center (PIFSC) and Hawaiian Islands Humpback Whale National Marine Sanctuary, the University of Hawaii at Manoa and Hilo, the University of Hawaii Joint Institute for Marine and Atmospheric Research, and Duke University. The cruise is being led by PIFSC research oceanographer Phoebe Woodworth-Jefcoats.

One of the primary goals of the survey is to learn more about how cetacean habitat varies throughout the Kona system. In particular, the research team is investigating north-south and nearshore-offshore variations in habitat characteristics of dolphins and whales using several methods, including passive and active acoustics, imaging sonar, and visual marine mammal observers. Mid-water trawls and CTD casts will also be conducted.

Another aim of the IEA cruise is to provide training to marine science students and educators. To this end, eight graduate and two undergraduate students and a NOAA Teacher at Sea will be participating in the Kona IEA survey.

In the cetacean habitat surveys, visual marine mammal observers and passive acoustics will be used to locate and, to the extent possible, identify marine mammals present in the Kona system. While the Sette is traveling along a predetermined series of survey transects (shown in accompanying map), a hydrophone array will be towed behind the ship. The hydrophones receive and record cetacean calls, clicks, and whistles. Using this information, along with visual sightings of animals by observers, scientists are able to identify and locate cetaceans in the survey area.

While the passive acoustics of the hydrophone array provides information on the distribution of cetaceans, active acoustics methods use sound to learn more about cetaceans' forage base. A hull-mounted echo sounder emits pulses of sound that reflect off of forage organisms such as small fish, shrimp, and squid. These organisms aggregate into sound scattering layers (SSLs) and the intensity at which they reflect different frequencies of sound reveals information about the composition and density of organisms within each layer. To supplement information gathered by the ship's echo sounder, an imaging sonar will be lowered through the SSLs to obtain higher-resolution information on the density of prey organisms within the layers as well as information on species that are not well detected by the echo sounder.

This sample of a mid-water trawl catch from the 2011 Kona IEA survey shows the variety of smaller organisms that support larger 
                 components of the marine ecosystem including cetaceans.
This sample of a mid-water trawl catch from the 2011 Kona IEA survey shows the variety of smaller organisms that support larger components of the marine ecosystem including cetaceans.
The CTD profiler is prepared for deployment on the NOAA Ship Oscar Elton Sette.
The CTD profiler is prepared for deployment on the NOAA Ship Oscar Elton Sette.

To help scientists understand what kinds and sizes of organisms are present in the SSLs, the research team is conducting mid-water trawls at each designated sampling station along the survey transects. The trawl catch is used both to improve interpretation of the active acoustic data and to learn more about the distribution of small and larval fish, shrimp, squid, and other small marine animals. Our previous Kona survey indicated that both composition and abundance of forage organisms change based on factors such as location, depth, moon phase, and ocean currents. Gathering additional trawl data may help tease apart the effects of these influences.

Scientists on the Sette will use a CTD profiler equipped with a rosette of sampling bottles to gather information on the physical and biological oceanography in the water column at designated sampling locations. As it is deployed through the water column, the CTD profiler measures sea water conductivity (to determine salinity), temperature, and depth (by measuring pressure), as well as dissolved oxygen and fluorescence (to determine relative abundance of phytoplankton). At several discrete depths, water samples are collected by the bottles and analyzed on board the ship to measure both chlorophyll content and phytoplankton size composition.

By carefully analyzing the data gathered through these many sampling methods, the researchers hope to gain new insights into the variations in cetacean habitat in the Kona system and the factors that influence them. The data will also build on information collected during the 2011 Kona IEA survey to provide a more thorough assessment of the physical, chemical, and biological oceanography of the Kona marine ecosystem. You can learn more about the Kona Integrated Ecosystem Assessment project at http://www.pifsc.noaa.gov/west_hawaii_iea/ and follow the cruise's progress on the PIFSC blog.