Acoustic tags are surgically implanted in striped bass.
The tags are 16mm by 80 mm - approximately the size of a tube of
lipstick. Each tag has a wax coating, which prevents
the fish's immune system from rejecting it.
The tags carry a two-year life battery and a transmitter that
"pings" an identifying code.
The sound produced is so high in frequency that the human ear cannot hear it, but
it travels out of the fish
and through the water to as far as half a kilometer away, loud enough for the
hydrophones to detect it.
Hydrophones, which are underwater microphones,
are hung from buoys at fixed
listening
posts, or checkpoints, throughout the Mullica River/Great Bay
Estuary.
These checkpoints are placed
mostly at narrow passages, such as Little Egg Inlet, so that fish
must pass through them
in order to move up or down river, or into or out of the coastal
ocean.
Scientists can compare the fish's movement with information they have
collected on the ocean or estuary environment. They collect this information by using
instruments from the
LEO-15 (Long-Term Ecosystem Observatory) that
measure and record information on light, water
temperature, salinity, wave height,
plankton blooms, chemical levels, wind direction and more; the
REMUS vehicle (an underwater moving instrument that can detect
objects along the ocean floor); and
YSI data loggers, which are placed throughout the Jacques
Cousteau National Estuarine
Research Reserve (JCNERR) and record water quality information approximately
every 15 seconds. Comparing this type of
data to the striped bass' movement patterns can lead scientists to
important conclusions about how
striped bass are affected by the environment around them.
Hydrophones will be able to pick up the noise coming from a tagged
striped bass. These "underwater microphones" will be hung from buoys at
various checkpoints throughout the study area, which includes the
Mullica
River/Great Bay
Estuary and the waterways that lead out into the ocean
or into nearby estuaries, such as Little Egg Inlet, Little Egg Harbor
and the Inter-Coastal Waterway towards Atlantic
City. When an
acoustically
tagged striped bass
swims near the checkpoint, the hydrophones "hear" the pinged code and pass the signal from a self-contained radio through an antenna on the buoy.
A receiving antenna at one of several places (a tower at the Rutgers University Marine Field Station, on the Parkway Bridge,
or at Lower Bank Bridge) picks up the signal and passes it by cell phone to a computer. That computer then records in a database
the fish's identifying code and the checkpoint where it was detected.
Because many of the
hydrophones are placed at these entrances
and exits of the Mullica River/Great
Bay
Estuary, scientists can find out not only when a striped bass is
leaving the estuary, but also the direction in which it is headed. In the same way, if and when the striped bass
returns, the scientists will be able to tell the direction from which it
is coming. Additionally, tagged fish that swim past these entrances
can be picked up by the hydrophones. So, even if they do not actually
enter the estuary, their approximate speed and direction can still be recorded.
