Q: Do the receivers constantly listen? Do the transmitters constantly ping?
A: The receivers are constantly listening for the transmitters. Anytime a fish implanted with an acoustic transmitter (tag) enters the detection range of a receiver it will be recorded. The detection range in Gray’s Reef National Marine Sanctuary is estimated to be 200 meters in any direction. The transmitters do not constantly ping, but they do have a consistent system. They will send out a signal every 120 seconds, regardless if they are within the 200 meter detection range of a receiver or not.

Q: Do the tags harm the fish? Do they behave normally?
A: This is a very important question that specific studies have been designed to try and answer. When fish are in pain, sick, or stressed, they do not behave normally. They will refuse to eat, swim, school, mate, or otherwise behave as we would expect them to. All of these activities are things fish need to do to survive. Studies have shown that fish that survive the initial tagging recovery period of about 48 hours will return to normal behavior. These studies have also shown that tagged and untagged fish do not exhibit any difference in behavior from one another or from what is considered normal.

Q: Does the fish feel anything when the tag transmits the “ping”?
A: Various studies have found no evidence that a fish feels anything from the transmissions. Since fish cannot tell us this answer to this question, we have to infer it from their behavior. Observations made during these studies have shown no alteration in behavior or any response to the ping. Also, these pings occur at a frequency of 69 kHz and have a very small power output. The combinations of the two suggest that the signal is too weak to be felt by the fish.

Q: Does the surgery harm the fish?
A: Surgical implantation of the acoustic tags is not without impact to fish. It requires longer handling times, more invasive procedures, long initial recovery periods, and the risk of infection. However the alternative, attaching the tags externally, also impacts the fish. External tagging procedures can disrupt the balance of the fish, cause abrasions or snag on objects. Also, external tags can affect swimming speed and increase energy expenditure. Comparing the different attachment alternatives, we decided that surgically implanting tags was the preferred option. It would be very counterproductive for our research to negatively impact our subject matter, so we make every effort to insure that the tagging does NOT significantly injure or impact the fish.

Q: How far away can we monitor a tagged fish?
A: The distance from a receiver that a tag can be detected depends upon a number of variables. The weather, visibility, and currents can dramatically change the detection range of the receiver by changing the acoustic environment. Waves, boat motors and noise from other organisms can interfere with a tag’s acoustic signal. It also varies with the area, since reef ledges, wrecks, artificial reefs, and other such underwater structures can block a signal. To determine what is best in a particular area, a range test must be done. Our range tests determine that we can detect fish about 200 meters away, reliably.

Q: Can we hear the transmitters?
A: You cannot hear it from inside the fish. The tags emit a signal at a frequency is barely detectable by human ears. If a transmitter is held close to your ear with no other sound around, then you might faintly here a clicking noise.

Q: How long do the transmitters last?
A: The life span on a transmitter varies with the ping rate, frequency, storage time, power output, and extreme temperature can significant shorten the lifespan. The tags used at Gray’s Reef have an estimated life span of about 2 years.

Q: How do we collect the data?
A: The receivers collect the "pings" from individual fish when they are located within the detection range of a receiver. This data point is recorded in the receiver's flash memory software, along with the data and time the event occurred. The receivers must be brought to the surface to retrieve these data. For this study, the receivers are currently collected by divers about every 3 months. The data is then downloaded from the receiver to a computer and then the receiver is placed back into the field. Once the data is on the computer, it is ready to be analyzed.

Q: How do you identify the fish on the data?
A: Each fish's tag sends out a unique signal. When the signal is picked up by the receiver, the receiver "recognizes" the signal and reports the corresponding tag id, along with the data and time of event.