The world is small and finite – even for a bluefin tuna that was tagged almost a year ago on the Croatia coast and then caught again (joe) The world is small and finite – even for a bluefin tuna that was tagged almost a year ago on the Croatia coast and then caught again. On August 5, I got an e-mail from “Blueeye,” informing me that skipper Marinco had caught a 1.5 meter, 55 kilogram tuna near the lighthouse of Blitvenica wearing a spaghetti tag on its back with the number HM093607. He asked if I could forward the message to the U.S., because of my “good contacts.” I told him, sure, I could do that, and that is why I am writing this exciting (at least for me) story.
Because of the time difference, the next day I called the U.S. fisheries authority, NOAA, in Florida, where fisheries biologist Eric Orbesen took the message of the “recaptured tag.” I reported to him the tag number HM093607, that the tuna was 150 cm in length and weighed 55 kg, and that skipper Marinco Pavlic had caught him on his boat, the CHARLI, on the 5th of August at a position 43 34N and 15 32E. When I asked if he knew when and where the fish had been tagged, Eric relied yes, he had already found the tag number in the PC. It had been previously caught by a certain Axel Nanko. He had tagged the fish on April 9, 2012 at the position 43 33N and 15 31E and estimated the weight to be 100 lb with a length of about 130 cm. “Axel Nanko is a friend of mine,” I told Eric, and we were both amazed. But I also said that the date of capture surprised me, because it was strange to find bluefins at Jezera in April. I asked if it was possible that the dates of the two entries entered in the PC were backward. We Europeans always write the day first and then the month and not vice versa as the Americans do. September was also the main fishing month Croatia. Because Eric could provide no answer to this, I called Axel and received from him not only the photo of the tuna show above, but also the following picture of the tag card, which he had luckily shot as well:
It was clear. Axel had tagged the tuna on September 4, only a few kilometers from the location where skipper Marinco eventually found him eleven months later. Eric was happy to get the information about the correct date. The accurate information about the growth is much more important than conjecture, which Axel had only provided as an estimated, albeit a good one. For the fish to be caught again at almost the same location a year later provides a strong argument for so-called homing behavior. Tuna migrate seasonally into and through the Adriatic to rich hunting areas. When I asked where they go when they leave the Adriatic, Eric sent me the following map with the trails of two tuna in the sea:
Both fish were tagged with transmitters in late September 2009. The small fish (red line) traveled up the Adriatic until the transmitter dropped off after three months. The larger one, a sexually mature tuna, behaved similarly in the first month, but then turned around and swam a total of 172 days to the Libyan coast at the eastern end of the Great Syrtis. It did so probably to reproduce, because it has long been assumed that these are the spawning grounds of bluefin tuna If this thesis is correct, however, the fate of tuna stocks in Croatia is now decided by the illegal tuna fishing off Libya. Since the end of Muammar Gaddafi' regime, illegal fishermen from all over the world have been cavorted in the Great Syrtis. There was no control at all at first. The activities of the pirate vessels were revealed by environmental activist, Paul Watson, and his SEA SHEPHERD. In 2010, he freed 800 bluefin tuna from nets that had been illegally caught by poachers off Libya. And they won the court case that a Maltese company had launched against them.
The following year, the SEA SHEPHERD was in a “battle” with two pirate ships. The environmental activists responded to the missiles and iron chain links of the pirates with stink bombs of butyric acid. Meanwhile, French and Maltese warships monitor the region for illegal fishing. Apparently with success. Because the EU and ICCAT have heavily restricted industrial fishing with seine nets in the Mediterranean, the bluefins stocks are growing. Even on the Croatian coast. A few years ago, 5 days of fishing were needed to catch a tuna. This August, good anglers are releasing several tuna in one day! And the fish are getting ever bigger. Eric calls for fishermen to tag and release the fish in order to explore the migration routes of bluefins in the Adriatic. I can supply of the spaghetti tags for those who want to participate. Perhaps an exciting story is waiting to be told from which much can be learned. Just how easy it is to make a tag after shooting a souvenir photo is shown in Axel's video of his second tagged fish, which is now likely swimming near Blitvenica. Video from Axel