The first tagging experiment on fish with Star-Odd's tags was carried out in Icelandic waters in 1993 on Atlantic salmon (Salmo salar L.). In addition, the tags have been used in Icelandic waters on Atlantic sea trout (Salmo trutta L.), Atlantic cod (Gadus morhua) and on Baltic salmon (Salmo salar L.) since 1995 and Arctic charr (Salvelinus alpinus) since 1997. Using the smallest of DST enables researchers to tag fish which are about 20 cm in length. In the salmon experiments the aim was to study the homing migration pattern in coastal waters and the sea (feeding) migration pattern of sea trout (citations).
Star Oddi DSTs have been used Cod (Gadus morhua) (Palsson &Thorsteinsson 2003, Thorsteinsson 1995, Thorsteinsson and Marteinsdottir 1998).. Saithe (Pollachius virens), Anglerfish (Lophius piscatorius L) and Plaice (Pleuronectes platessa L). Using underwater Tagging Device (from SO) some Ocean read fish species (Sebastes mentella) have now been released with small DSTs.
Methods
Preparations:
Depending on the country involved, various legislations may apply to tagging experiments with electronic tags. The CATAG report (Thorsteinsson 2002, http://www.hafro.is/catag/index.shtml) gives overview of tags, tagging, relevant legislation and fish welfare issues. See also www.nal.usda.gov/awic) The use of anaesthetics is frequently used and is compulsory in some countries when surgery or intrusive methods are used applying an electronic tag. It is very often needed to reduce or stop movements of fish during handling. Some avoid using anaesthetics as they might not be necessary or even detrimental in special experimental conditions. In such cases other measures are used to try to minimise the effect of capture, tagging and release procedures on the fish.
External Tagging (Salmonids): After the fish has been anaesthetised (e.g. 0.1% MS-222), it is placed in a special box with support on both sides (drawing available from Star Oddi). The fish is kept submerged in a low concentration anaesthetic solution (e.g. 0.05% MS-222). Two needles are pushed through the dorsum of the fish close to or in front of the dorsal fin. The spacing between the needles should match the length of the tag. The attachment wire of the tag (steel threading-0.5 or 0.6 mm) is threaded through each needle and fastened on the other side of the fish. Where the steel threading comes in contact with the fish, it is placed in a plastic tube to prevent erosion of the flesh by the attachment wire. After the surgery, the fish are allowed to recover in water that has no anaesthesia and are then released.
Internal tagging: If anaesthetics are used the application is more or less the same as the one for external tagging above. After the fish has been anaesthetised, it is placed on its dorsum in a V shaped surgical saddle and operated on. At the Marine Research Institute (Reykjavik) a method has been developed for surgical application of DSTs to Atlantic cod where no anaesthetics are used. This method has been accepted by the Icelandic committee for treatment of experimental animals. Experience has shown that if cod are placed and stabilised dorsal side down, like happens in the V shaped tagging-saddle there is very little movement is seen and no reaction to the surery. After the surgery, the cod can be released directly into the sea or kept for surveilance but the time the fish has to be kept onboard the tagging vessel is greatly reduced. During the surgery, oxygenated water is directed through the mouth and over the gills. The eyes of the fish are protected and kept moist by covering with a pre-soaked towel. An incision is made 3 cm from the mid-ventral line and anterior to the pelvic fins. A needle is inserted through the body wall close to the incision, and the plastic identification tube from the tag is then threaded into the hollow needle to the outside. The tag is inserted into the body cavity and the incision is closed with sutures. The fish is then released directly into the water, or after a recovery time if needed.
More detailed information can be obtained from Star-Oddi concerning both of these methods. For long time measurements, internal tagging is recommended. There have been almost no reports of tag loss from the fish or of wounds related to the tags. It is also known that the external tag can "grow" out of the fish. How fast the tag will grow out of the fish is highly dependent on the growth rate of the fish. This means that even if the fish is never captured the fish will, eventually, get rid of the tag.
Recapture of the DST electronic tags is considerable higher than that of conventional ones. There are probably two reasons for this. The first one is that the DSTs are very easy to see on the fish and look very "advanced". The second reason is that in most cases a reward is issued for the return of the tags.
The flatfish species plaice was tagged with the Icelandic Data Storage Tags for the first time in April 1998 in Breidafjordur on the west coast of Iceland. Breidafjordur is one of the spawning grounds for plaice in Iceland. This is the first time a flatfish was tagged with our tags (DST 300), and therefore some of the tagging technique had to be developed as the same can't be used on flatfish as on other fish species. The experiment was carried out by fisheries scientists from the Marine Research Institute in Iceland, the second phase of the tagging experiment was carried out in August 1998.
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