Tagging flatfish can be a little different than tagging a round fish. Below is a description of how we placed the archival tags on the winter flounder.
Step 1) Catch the fish. For this we used a commercial trawl boat, the Viking II which unfortunately just sank. The trawl catches bottom fish and brings it onto the boat for us to sort through and find the winter flounder.
Step 2) Put the fish in a live-well which is a large plastic box that holds water to keep the fish alive. Here we can asses to see how healthy the fish is. We only want to tag the healthiest fish.
Step 3) Measure the length of the fish. We aimed for greater than 30cm because the tags are rather large.
Step 4) Next we place the fish on a board with hollow needles fastened in it. These needles put holes in the fish which we can then thread wire through the body to attach the tag. This may sound rough, but the majority of the fish don’t even bleed from the procedure. Its a lot like piercing someones ear. We want to place the fish as close to the center as possible without being on the vertebrae so that the center of the weight is balanced, which is best for the fish to swim normally.
Step 5) Once the wires are through we can flip the fish over on its underside. On this side of the fish we thread a second piece of plastic on the underside so that the wires don’t rub the skin. The cool cloth over the fish’s head helps to calm it.
Step 6) We use a standard ruler as a separator between the body of the fish and the plastic, then bend the wires in place. The ruler helps to make sure the wires are not too tight on the fish to make it as comfortable as possible. We can now twist the wires, bend them down, and trim the ends so they don’t scratch the fish. The fish now goes back into the live-well to relax before its release.
Step 7) Now the moment that the fish have been waiting for, their release. For this we use long handle nets to get them as close to the water as possible. We record the location of their release to see how far and in what direction they move.
Step 8) Now we just have to wait for the fish to be re-captured. From the tags we can asses where the fish like to live. The tags record temperature, salinity, and depth over time. The graph below show depth vs. time with the colored points as temperature. In the two weeks this fish was over you can see that once the water warmed up it moved into deeper cooler water.