engleski

Report on research activities on bluefin tuna tagging within growth-out farming cages

Results from a tagging study conducted in two different Croatian farming places during the period 2002-2005 are presented. In total, 190 fish were used in this research. Based on the overall amount of data collected (initial weight, days in captivity, mortality, final weight) and analyzed up to now, it is evident that handling procedures and devices used could play a key role in tagging success. It seems that cotton fabric in contact with the skin of tuna damages the mucus layer, causing the death of the fish in the next few days. It can be concluded that such a device should be avoided in handling live tunas. Also, the relatively large number of fish that lost (expelled) their tags after longer farming periods suggests that the conventional "spaghetti" tags used are not very suitable. It is suggested that two-barb anchors or another type of anchor and/or tags be used in order to improve the tag retention. Regarding growth, it is evident that fish increased in size considerably during the farming period. (e.g. tagged fish of age 1 after 510-530 days increased their weights by 3-4 times and their lengths by 37-49 cm). Notwithstanding, tagging seems to have a negative influence on overall growth and tagged fish increased their weight less than other fish in the cage. After tagging fish have a negative growth rate due to starvation and only after 2-3 months are able to recover the initial biomass.

bluefin tuna; tagging; farming cages

ICCAT = International Commission for the Conservation of the Atlantic Tuna