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SCRS/2003/140 Col. Vol. Sci. Pap. ICCAT, 56(3): 1218-1221 (2004)

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SOME DIFFICULTIES IN SAMPLING AND TAGGING LIVE BLUEFIN TUNA IN

THE GROWTH-OUT FLOATING CAGES

Ticina, Vjekoslav1, Leon Grubiic1, Ivan Katavic2, Ivana Miletic3, Ivor Jeftimijades3, Vanja Emric Ticina,Vlasta Franicevic2

SUMMARY

This paper describes some difficulties that were encountered in the second year of the researchon bluefin tuna farming activities in the Adriatic Sea. According to the proposed research plan,initial tagging data on the size of fish released back into cage are presented. As a consequenceof handling procedures, 8 out of 33 fish died resulting in tagging mortality rate of 24.2%.

RSUM

Le prsent document dcrit certaines difficults rencontres durant la seconde anne du programme de recherche sur les activits dlevage de thon rouge en Mer Adriatique.Conformment au programme de recherche propos, il prsente les donnes de marquageinitiales sur la taille des poissons remis en cage. A la suite des procdures de manipulation, 8

poissons sur 33 sont morts, entranant un taux de mortalit de marquage de 24,2%.

RESUMEN

Este trabajo describe algunas dificultades encontradas durante el segundo ao de investigacinsobre las actividades de cra del atn rojo en el Adritico. Segn el plan de investigacin

propuesto, se presentan los datos de marcado iniciales sobre la talla de los peces liberados denuevo en la jaula. Como consecuencia de los procedimientos de manipulacin, 8 de 33 peces

murieron, es decir una tasa de mortalidad por marcado del 24,2%.

KEYWORDS

Aquaculture techniques, feeding behaviour, bait fishing, tagging mortality, tuna fisheries

1 Institute of Oceanography and Fisheries, et. I. Merovica 63, 21000 Split, Croatia (E-mail: ticina@izor.hr )2 Directorate of Fisheries, Ministry of Agriculture and Forestry of Republic of Croatia3 SARDINA d.o.o., Postira, Croatia

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1 Introduction

Since 1997, a new activities in aquaculture concerning the bluefin tuna (Thunnus thynnus) rearing in the floatingcages, took place on the eastern part of the Adriatic Sea (Katavic et al., 2003). In the last few years, the rapiddevelopment of this practice of the bluefin tuna farming in the Adriatic has been noticed. Recently, almost thewhole catch of bluefin tuna from the eastern Adriatic Sea has been transferred into floating cages for farming

purposes.

It should be considered that this practice could cause difficulties in terms of the catch statistics and concurrenceof catch data with trade data. Tuna farming should be recognised as a very important issue in the future(particularly in the Adriatic Sea), and it will be necessary to improve Bluefin Tuna Statistical Document(BTSD). This improvement should be based on some specific knowledge about tuna farming activities andgrowth patterns of tunas in the captivity.

Currently, within framework of ICCAT Bluefin Year Programme, a study on the growth rates of bluefin tunareared in the growth-out floating cages is under way. First results of this research have been presented by Ticinaet al. (2003). Here, some difficulties that were experienced during second year of the research, are described inthis paper.

2 Objectives

According to the proposed research plan, the objective during 2nd year of the research was sampling and tagging50 specimens within second size group, with their average weight of 10 kg, i.e. about 500 kg of bluefin tunaslive weight.

3 Material and methods

The fish of similar size included in this research were caught by purse seine during April and June 2003 in theeastern central Adriatic and have been kept in two cages. For tagging purpose, tunas in the cage were fished byhook and monofilament line, using pilchards and small mackerels as bait. Fish were measured in fork length and

weighted using hanging scale for quick weight check and cradle like device (Ticina et al., 2003). ConventionalICCAT tags were used.

4 Results

In accordance with the proposed research plan, during the second year of the research activities in the AdriaticSea, 50 fish of approximately 10.0 kg in live weight, that belongs to the 2nd size group (Age class: 1), shouldhave been tagged with conventional ICCAT tags. However, due to the fact that tunas of wanted size were notavailable, smaller number of somewhat bigger specimens were taken in random sampling.

During year 2003 we faced various difficulties in sampling and tagging bluefin tunas in the growth-out floatingcages. As we already noticed last year, it was not possible to carry out sampling and tagging immediately upon

their transfer from the fishing grounds to the cage site, because the fish were under stress and would not acceptthe bait. But, even after a certain acclimatization period, fishing for these tunas (2nd size group) in the cage byhook and monofilament nylon lines was not as successful as it was previous year with smaller specimens.

At the beginning of tuna sampling activities (i.e. fishing) by hook and line, fish were attracted by throwing acertain amount of bait in the cage, with aim to provoke their appetite. However, it was noticed lack of interest forfeed, and also that these bigger tunas were far more cautious towards the bait on the hook than smallerspecimens. Consequently, we needed to throw bigger quantity of feed into cage (together with baited hook) toattract more tunas, thus provoking their aggressive appetite that in turn reduced their caution. After beinghooked, their reaction was very strong furious jerking motion that probably affected other fish in the cage.Compared with sampling conducted in the 2002 year when smaller tunas were hooked frequently every 2 or 3minutes, this year sampling by hook and line resulted with infrequent sporadic catches.

Perhaps lack of interest for food of tunas in the cages could be explained by unusual environmental conditionsthat occurred this year. The average sea temperatures during June, July and August were 23.6C, 24.8C and

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24,5C respectively, with maximum values up to 28C. The increased water temperature, long period withoutrains and insufficient water mass dynamic resulted in thermal stratification with strong thermocline formed at theapproximately depth of 8 meters. Furthermore, the cause could be the bait and/or feed quality (not fresh butdefrosted feed was used), but also the simple fact that older and more experienced fish are normally morecautions than younger specimens. It is presumed that all these circumstances together effect on fish in the waythat has resulted in reduced hooking efficiency.

Finally, after several attempts, 33 fish were sampled and tagged (Table 1 ) this year in two cages. In the cage thatcontained tunas caught during spring season, 17 fish were tagged. These fish ranged from 12.0 to 18.0 kg inweight, and from 80 to 89 cm in fork length. It is presumed that these fish will be fed in the cage duringapproximately 18 months rearing period. Other 16 fish were sampled and tagged in the cage with tunas caught atthe end of June 2003. These fish, ranged from 8.5 to 20.5 kg in weight and from 77 to 97 cm in fork length,should be harvested after a shorter rearing period. All together, the total weight of 33 tagged fish was 487.0 kg inlive weight, that in average results with 14.76 kg of fish live weight. Until now, the total of 8 out of these 33tagged fish died, indicating a sampling mortality rate of 24.2%.

References

KATAVIC, I., V. Ticina, L. Grubiic, V. Franicevic. 2003. Tuna farming as a new archivement in mariculture ofCroatia. In: ORAY, I.K. and KARAKULAK, F.S. (Eds.), 2003. Workshop on Farming, Management andConservation of Bluefin Tuna, Turkish Marine Research Foundation, Istanbul TURKEY, PublicationNo. 13: 10-20.

TICINA, V., L. Grubiic, I. Katavic, I. Jeftimijades, V. Franicevic. 2003. Tagging of small bluefin tuna in thegrowth-out floating cage - report of the research activities on tuna farming in the Adriatic sea during2002. ICCAT Coll. Vol. Sci. Pap., 55(3): 1278-1281.

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Table 1. Tagging data and related mortality data of bluefin tuna released back into growth-out floating cageduring 2003 year.

Fish TAGGING TAG LF WEIGHT MORTALITY

No. DATE NUMBER (cm) (kg) DATE

1 05.06 2003. CT-07445 80 13.5

2 05.06 2003. CT-07440 87 17.03 05.06 2003. CT-07439 84 15.04 05.06 2003. CT-07436 88 18.0

5 05.06 2003. CT-07431 87 17.06 05.06 2003. CT-07430 80 14.57 05.06 2003. CT-07428 88 17.58 05.06 2003. CT-07425 80 14.09 05.06 2003. CT-07449 87 17.0 08.06.2003.

10. 05.06 2003. CT-07432 83 14.5 08.06.2003.

11. 05.06 2003. CT-07435 89 18.0

12. 18.06.2003. CT-07422 84 14.013. 18.06.2003. CT-07443 86 13.514. 18.06.2003. CT-07427 89 16.015. 18.06.2003. CT-07438 81 12.016. 18.06.2003. CT-07446 84 14.017. 18.06.2003. CT-07433 84 14.5 20.06.2003.

18. 21.07.2003. CT-07448 77 8.5

19. 21.07.2003. CT-07401 81 12.5 24.07.2003.

20. 21.07.2003. CT-07404 82 13.0 24.07.2003.

21. 21.07.2003. CT-07408 82 13.5

22. 21.07.2003. CT-07420 94 15.5

23. 21.07.2003. CT-07412 96 17.0

24. 21.07.2003. CT-07415 85 13.5

25. 21.07.2003. CT-07418 85 13.5

26. 06.08.2003. CT-07437 97 20.5

27. 06.08.2003. CT-07442 85 13.5 06.08.2003.

28. 06.08.2003. CT-07434 97 18.5

29. 06.08.2003. CT-07441 91 13.5 09.08.2003.

30. 06.08.2003. CT-07447 95 16.0

31. 06.08.2003. CT-07429 89 14.5

32. 06.08.2003. CT-07427 86 14.0

33. 06.08.2003. CT-07444 92 14.5 09.08.2003.

TOTAL: 487.0 kg