Project Title: Passive Acoustic
Applications in Marine Fisheries
Sea Grant, Rodney Rountree, UMass/Dartmouth
and Tony Hawkins, University of Aberdeen, King's College,
Research Protocol Outline
the fall of 2002, the proposers began a project titled "The
Identification of Cod and Haddock Spawning Habitat Using Passive
Acoustics" sponsored by the Northeast Consortium. Under
this project we have developed innovative, low-cost Autonomous
Underwater Listening Stations (AULS). The AULS hardware is specifically
designed for deployment from commercial fishing vessels.They
are built around state-of-the-art digital recording devices know
as Nomad Jukeboxes by Creative Laboratories which employ 10 GB
hard drives to store over 60 hours of acoustic data.
CFER Autonomous Underwater Listening Station (AULS) with
10 GB Nomad.
The Nomad, gel cell,
and custom interface circuitry fit into a compact pressure housing
made from polyethylene gas pipe end caps machined to accommodate
am O-ring and held together with a band clamp. The housings have
been pressure tested to the equivalent of 250m of seawater. With
an external hydrophone/preamplifier, the units cost under $1,000
each. Six AULS units have been built under the project and additional
Nomad units are being used as replaceable storage media to shuttle
data from the boats to MIT for uploading and processing.
To facilitate the deployment
of the AULS, galvanized steel bottom mounts have been built that
weigh 60 pounds and protect the housing from impact by other
fishing gear. Pictured in Figure 2, these units are rigged much
like passive fishing gear, placed between two anchors and two
During April and May,
we have taken advantage of know spawning grounds around Gloucester.
In June, the fieldwork was expanded to the north with deployments
out of Sebasco, Maine.
To date, the placement
of the units has been based on the knowledge of the participating
fishermen of historical spawning aggregations, current catch
reports from commercial and recreational fishermen, and on bycatch
reports from lobstermen. The participating fishermen are also
using hook and line to verify the presence of fish.
AULS installed in its protective steel bottom mount.
The normal practice
is to leave the AULS deployed for two days, then return to service
the unit and redeploy it in the same or a nearby location. The
Nomads will capture a maximum of 218 fifteen-minute files, or
54.5 hours of continuous two-channel data when set on its lowest
11,025 Hz., 12-bit sampling rate.
The AULS units use
HTI (High Tcch Industries, Gulfport, MS) hydrophones which have
have built-in preamplifiers that provide sufficient gain to yield 165
dB per volt at 1 mPa. The Nomads have a user-adjustable gain
setting from 1 to 15, which we leave on the highest setting.
This combination provides excellent sensitivity, but which can
saturate during deployment and retrieval, during the nearby passage
of vessels, and during some marine mammal calls.
During servicing, the
Nomad, two 6-volt lead-acid gel cells, and two 9-volt
transistor batteries for the hydrophone preamplifier are replaced.
The Nomad is then returned to MIT for uploading and analysis.
Uploading of the files takes approximately 4 hours using a USB
port and Creative Laboratorys file transfer software.
We are using Cool Edit
2000 software (Centrillium) for our preliminary analysis. This
process involves a visual inspection of the waveform of each
43,000 MB file and listening to passages that appear interesting
or have the characteristics of fish sounds. We are working on
developing an automatic identification system that will scan
the files for sounds that match the acoustic parameters of species
of interest. For this process, we are using Ishmael, a software
developed at the Pacific Marine Environmental Laboratory for
processing acoustic files (Mellinger 2002). Using spectrogram
correlation (Mellinger and Clark 2000) we will soon be able to
scan our recordings and have passages that match know vocalizations
of cod and haddock identified and the statistics on their occurrence
Of course, there are
much more than fish vocalizations captured by our broadband,
omni-directional hydrophone. At times passing vessels or noise
from weather-induced sea state dominate the acoustic environment
and makes fish sound detection impossible.