Anaesthesia and tagging
Operating receiving stations and transmitter search
Use of biotelemetry transmitters
Test study
Use of data storage tags: DST
27. The organization of these sessions during the workshop is described sequentially. In practice, sessions were repeated several times so that participants could improve their know-how in the fields that required more practice. The chronological list of the various tasks can be found in the agenda (Annex 3).
28. In the first practical session, participants learnt how to stitch on a polystyrene plate (photo 8) in order to understand the procedure to close an incision. They then practiced anaesthetics and abdominal surgery on cichlids (tilapias) and clariids (sharptooth catfish Clarias gariepinus) stocked at the ODRS fish-farm. These two groups of species were chosen as they are representative of West African fisheries. This operation was repeated during the workshop so that participants could master implanting telemetry transmitters and could test various fish size and tagging equipment (suture threads, needles of different types). Tagged fish were released into a pond through which there is a continuous flow of water from the Sélingué dam.
29. Fish (Tilapia, Clarias and Auchenoglanis sp.) tagged by training staff and equipped with data storage tags and telemetry transmitters were also released in the pond, their signals being recorded by a passive listening station set up within the boundaries of the fish-farm. Data loggers recorded the water temperature at the surface and at depth as well as the light intensity at the water surface every five minutes for a week. The first objective of this operation was for participants to be able to compare different methods of biotelemetric measurements (radio transmitters vs. data storage tags) and to compare biological and environmental information during group sessions (cf. section “use of telemetry transmitters”).
30. During the second week of the workshop, the pond was drained and tagged fish were checked and participants could evaluate objectively the quality of the tagging and any improvement they needed to make before applying the technique in a project.
31. The operation and use of receiving stations was summarized and illustrated with various types of receivers and antennae (loop, Yagi, M-Yagi) operating on different carrier frequencies (49 and 151 MHz). In order to familiarize participants with transmitter search at both long and very short distance, two sessions of “fox hunting” (i.e. searching for scattered transmitters; photo 9) were organized around the lake of Sélingué and within the ODRS fish-farm. Participants were thus able to assess their progress from one session to the next and were confronted with the different practical situations that they are likely to come across during projects, whether localizing live fish or recovering transmitters from fish caught by fishermen or predators.
32. Participants were able to use three main types of telemetry transmitter, measuring temperature, depth and fish activity. For each type of transmitter, they undertook a calibration which consisted of determining the variations in the interpulse interval in connection with the measured variable. Depth calibration was done in the lake of the Sélingué dam (0-18m) and the temperature calibration from a mixture of waters of different temperatures (15-32°C). In the case of activity transmitters, the calibration was established from static and active transmitters in order to determine the minimum and maximum pulse rates and complementary measurements were made on fish which had been tagged and were held captive in the aquarium so as to identify the minimum movements necessary to trigger a fast pulse rate. Calibration curves were then analysed on a computer in order to determine linear regressions to be used to interpret results collected by an automatic passive listening station.
33. An automatic signal recording station, consisting of an ATS Challenger 2100 receiver, a DCC II computer and a loop antenna (photo 10), was programmed to record signals from fish stocked in the ODRS pond during a 24 hour-cycle, for uninterrupted recording periods of 30 seconds per fish every five minutes. At the end of the recording, participants had the opportunity to download the station, to test if initial settings were adequate regarding reception gain and noise rejection, and finally to analyse the data collected by data storage tags and data loggers which measured the surface and depth temperatures.
34. These different stages gave the participants a better idea of the high level of performance of automatic passive listening stations but also of the need to program meticulously the reception gain in order to avoid biased information in their databases, which could modify the interpretation of the biological data.
35. A full-scale exercise, involving all the training staff and participants, was organized in the Sélinguéni pond. It aimed to familiarize participants with the different methods of positioning, area marking and cartography, this study consisted in:
36. By combining these different operations, participants were able to put into practice various important aspects of the theoretical teaching and to integrate them into a logical sequence essential to undertaking a structured program.
37. At the outset of the workshop, three fish (Tilapia, Clarias and Auchenoglanis sp.) were fitted with data storage tags (DST 200 and DST 300, Star-Oddi). These tags were attached dorsally and the fish were released into the ODRS pond. All the tags measured, at one-minute interval, the depth and ambient temperature of the habitat occupied by the fish. The tag on the catfish Clarias gariepus also measured the orientation of the fish compared to the horizontal, the difference between successive measurements providing an index of activity.
38. When the pond was drained, participants were able to compare the effects of external attachment (for DSTs; photo 11) to those of surgery (for telemetry transmitters of similar weight; photo 12) on fish health. Participants were then involved in the different stages of the procedure for downloading the data storage tags (cutting of the tags [photo 13], withdrawal of the internal memory, downloading to the computer [photo 14]) and they began to analyse the biological data in comparison with environmental information provided by data loggers and biotelemetric data collected by the automatic station.
39. From the analysis of the data collected by different telemetric systems, participants were able to compare their respective levels of performance in terms of accuracy, safety and recovery guarantee, which are essential factors in defining the structure of a project.
