Abstract. The range of PIT tags may be too small for general detection, however, it is interesting to use them in marking and recapture methods. The rate at which the tags were read was between 5 and 7 Hz. The maximum range was 17 centimeters out of the water and 10.8 centimeters in water. Five different tags were tested allowing the comparison of the individuals range of the tags.

Introduction

Studies on fish movements in the wild have been conducted using radio telemetry or electrofishing, which, in some cases, follow fish patterns of movement in streams or rivers. Difficulties arise in long term monitoring because radio transmitters have short-term battery power (usually less than 1 month). And, electrofishing, even if it does not kill fish or influence their behavior, is extremely labor intensive and must be done over an entire stream if all fish are to be detected. Alternatively, weirs have been used to capture fish as they move along streams, but this again is also labor intensive and sheds no light on movement between weirs. Thus, the objective of this paper is to evaluate the effectiveness of PIT tags in the identification of fish returning to a given location. PIT tags do not use batteries and are therefore assumed to be reliable for the duration of the life-span of the fish (Freeland, 1995). Laboratory experiments were conducted using PIT tags to determine the range of detection and software reliability. A great advantage of the PIT is the very low mortality of organisms dying from the tagging. Curves were plotted to show the optimal and maximum range of PIT tags in and out of the water.

Method

To evaluate the detection range of PIT tags, we used an evaluation kit from Texas Instruments TIRIS (radio frequency identification technology) and constructed a wood tank 8ft x 1ft x 1ft for underwater tests.

• Test on the PIT tags

PIT tags were tested to see if they were functional and also the distance that they would cover while in the air and underwater. We received 5 different tags from Texas Instruments with different features. The first three tags were 30 millimeters long and 4 millimeters wide, and were divided into 3 categories: read only (RI-TRP-RR2B), read and write (RI-TRP-WR2B), and Multipage (RI-TRP-CB2B). The two other tags were 23 millimeters long and 4 millimeters wide: one was read only (RI-TRP-RRHB) and the second was read and write (RI-TRP-WRHB). We also received two different antennas. The first was a Gate antenna (RI-ANT-B01C), which was 710 millimeters long and 265 millimeters wide (Figure 2), and the second was a ferrite stick antenna (RI-ANT-S01C), which was 139 millimeters long and had a diameter of 19 millimeters.

• Reader and software use to detect the PIT tags

We used the S2000 reader which came in the evaluation kit, and was then connected to a Micron Millennia transportable computer. The program used was TRTE, which allowed a connection between the computer and the S2000 reader.
Baudrate = 9600
Parity = No Parity
Stopbits = 1 Stopbit
Databits = 8 bits

The program TRTE offered different modes of detection. The choice of modes was made in the Terminal mode. A single reading could be read by pressing X, and the line mode which gives a constant reading was used to determine the maximum range that the transponders had. The Gate mode was obtained by pressing G, and this mode received the first ID number and displayed the second one only if it was different from the first. The ID of tags in memory can then be cleared by pressing C.

• Multipage, Read and write PIT tags

The read and write PIT tags can hold specific information such as the location and time at which the fish was captured. This process takes place as follows: The first step is to read the ID number on the tag by pressing X. Pressing the key P allowed us to change the ID number. The program that we used always read an ID in decimal numbers, and for this reason the format should be changed, where this can be done by pressing F (Texas Instrument).
The S2000 reader had to be in multipage mode, and this was done by pressing K and then 1. Several pages can be read, up to 17, and they are read in the following manner: press X01 to read the first page and so on until X17. To re-write the content of one page, the writing mode needs to be activated, and this is done by pressing P. The page number needs to be entered so the content can then be changed.

• Importance of the orientation of the tags

We discovered that the orientation of the tag and the antennas is very important, and for this reason, four different types of orientation were tested for the gate (Figure 4-7)and the ferrite stick (figure 7-10) antennas. The tests were repeated in and out of the water. In each experiment, the PIT tag was moved until a maximum distance was reached (where the tag is barely detected) and an optimal distance where the computer finds a 100% detection.

Results

All tags were tested under laboratory conditions. Four different types of orientation were used to determine the optimal range of detection of the tags. We did not obtain any reading from the 23 millimeter tag read in water only. However, we did obtain readings from the same tag outside of the water. So, it was concluded that water strongly reduced the range of detection of this tag. The PIT tag having the best range was the 30 millimeter, read and write RI-TRP WR2B tag, both out and in the water (figures 1-8). The optimal position for the detection of the tag was orientation number 2. The distance for the minimum detection was about 17 centimeters in the air and 10.8 centimeters in the water. The gate antenna was better for detection underwater (figures 6 and 8) for position 2 than the Ferrite stick (figure 5 and 7). At position 2, perpendicular to the gate, the tag parallel to the ground showed the strongest detection ability, and it would therefore be easy to insert this tag next to the dorsal fin of the fish without any supposed problem

Discussion

The ferrite stick antenna, overall, has the best detection abilities of all orientations studied. However, orientation number four was the least desirable position for both antennas. We did not find any reason why the tag RRHB did not get any readings in water. But, it was observed that, in general, the tags read and write have a better range than the read only.
The range of detection detected by both of the antennae reveals itself too small to be used to detect fish in a river, at least in a conventional way. We could, on the other hand, check to see if a fish is coming back to the same location by placing the gate antenna in the river. The fish going through it would then be detected.


 
The PIT tags can also be used instead of regular tags which can be lost or where the algae grow. The main disadvantage of using PIT tags is the lack of submersible detection equipment. The wire making the connection between the antenna and the Reader is only about one meter. And, finally, the reader S2000 would not be appropriate for some field work since it needs electricity to work. Nevertheless, some other readers do exist.

Acknowledgements

I thank Dr. Emil Morhard for purchasing the material necessary to conduct this study and allow me to work in his lab.

References

Armstrong JD, 1996. A Flat-Bed Passive Integrated Transponder Antenna Array For Monitoring Behavior of Atlantic Salmon Parr and Other Fish. Journal of Fish Biology 48, p 539-541.
Freeland WJ, 1995. Suitability of passive integrated Transponder Tags For Marking Live Animals For Trade. Wildlife research 22(6), p767-773.
Knights BC, 1996. Effects of Implanted Transmitters On adult Bluegills At Two Temperatures. Transactions of the American Fisheries Society 125 (3), p 440-449.