The scientists' main
hypothesis in this
project is that different
contingents, or groupings, of
striped bass have different
migration patterns. One of the best ways
to test this hypothesis
is to track several individual striped bass over a long period of
time. Without tagging
telemetry,
this is extremely difficult
because the fish are hidden underwater and cannot be observed with
the naked eye. In addition, the
striped bass can travel great distances in a very short period of
time, sometimes at night and even
during storms,
making it impossible for scientists to follow them.
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In addition to the acoustic tag tracking, some of these striped bass
will also be followed closely by boat on a daily basis.
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By using
acoustic tags on the fish,
scientists can hear the fish even when
they cannot see them. Each tag contains a battery, which powers a tiny
speaker called a
transmitter that produces a series of
pulsing sounds. Each tag
produces a different pattern of these pulsing sounds, which becomes an
identification code for the
fish in which it is implanted, like a fingerprint.
The noise is
ultrasonic -
so high that the human ear cannot hear it.
Hydrophones, however, can detect this
noise.
Hydrophones are located at various
checkpoints
in the ocean, in the
estuary, and in the river
of our
study site in the
Jacques Cousteau
National Estuarine
Research Reserve (JCNERR).
Each time a hydrophone "hears" a tagged fish passing a checkpoint, it radios the detected
code back to a
central receiving station,
where a computer identifies the
fish and records its location.
For fisheries managers, it is extremely important to understand where
fish
migrate. This
is because, in order for them to set fishing regulations for a certain
area, they need to
know what the size of the fish population is for that area. If
scientists discover that
different groupings of striped bass have different migration patterns,
fishing regulations
should reflect these to keep all populations at healthy levels.
Let's look at an example of what this means. Imagine that in a specific estuary on the New Jersey Coast, there are three contingents of striped bass during the spawning season (the season that they reproduce). The first contingent spawns there, travels very far into the ocean and then returns to that estuary again for the spawning season the next year. The
second contingent does not leave that estuary at all for the entire year. And the last contingent spawns there, travels a
great distance, and ends up in a completely different estuary in Virginia for the next spawning season. This is the kind
of information that the fisheries manager for this estuary would need to know to have an understanding of just how many striped
bass there are at any given time of the year.
With the old way of tagging, it was impossible to learn where
these fish go throughout the
year and how often they go there. Scientists could only learn where
they ended up. Acoustic telemetry, however, will
give scientists the ability to know when the striped bass leave, how
often they leave, where they are headed,
and whether or not they return.
