Seaglider recovery update!

The joint UH-PIFSC Seaglider launched off Kona in early December was recovered on 2 January 2014.  During its nearly month-long deployment, the Seaglider made 135 dives that spanned the entire length of the Kona coast and collected numerous recordings of cetacean clicks and whistles.  In addition to collecting acoustic data, the glider collected environmental data such as temperature, salinity, current velocity, and chlorophyll concentration during each of its dives.  Now that the glider has been recovered, we can start comparing the acoustic data to the environmental data to determine where cetaceans are detected.  Ultimately, we’d like to figure out why cetaceans seem to be found in distinct “hotspots” along Kona.

Another goal of this mission was to learn how to make the best use of Seagliders on future missions.  After we’ve analyzed the acoustic data from this Seaglider deployment, we’ll redeploy the glider putting what we’ve learned to use.  Based on the depths, locations, and durations of recorded cetacean sounds, we can refine the glider’s sampling, or “listening”, routine.  Sound files are quite large, so the glider can’t record for its entire deployment.  Rather, the hydrophones turn on and off on a set schedule.  This schedule balances the need to collect enough recordings to determine how cetaceans are using their Kona habitat with details such as the hydrophones’ battery life and disk space.

Processing the acoustic data will take a bit of time, but we can begin to make some observations about the physical environment the glider encountered during its deployment.  For example, we see an abrupt shift in the current direction on dive 84, just after the glider passed south of 19.5°N.  This shift suggests that close to shore the current flow was along the coast – northward north of 19.5°N and southward south of 19.5°N.  We can also see that the depth of the greatest chlorophyll concentrations gets deeper as the glider moves off the Kohala Shelf around dive 60 and that the chlorophyll concentrations decreased while the glider was at its southwesternmost points from dives 110 – 120.  It will be interesting to pair these observations with the locations of cetaceans’ clicks and whistles to determine how they might be making use of these differences in their Kona habitat.

This glider mission was a collaboration between the University of Hawaii’s SOEST Ocean Glider program (http://hahana.soest.hawaii.edu/seagliders/) and the Kona Integrated Ecosystem Assessment (Kona IEA; http://www.pifsc.noaa.gov/kona_iea/).

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Fig. 1: Seaglider track (black dots) and planned transects (thick black lines).  The green dot shows the deployment site and the red dot shows the recovery site.  Depth is contoured in 500m intervals from 500 – 2000m.  The Seaglider completed the easternmost transect and the southern portion of the central transect on this deployment.  Future deployments will hopefully span all three transects.

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Fig. 2: Seaglider-measured currents.  Each barb shows the speed and direction of the depth-averaged current for one dive.

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Fig. 3: Seaglider-measured temperature and chlorophyll concentration.  The Seaglider’s early dives are shallow and get progressively deeper as the glider moves away from shore.  There were also a number of shallow dives performed throughout the deployment to test communications with different glider components.

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