MORPHOMETRIC RELATIONSHIPS OF FATTENING BLUEFIN TUNA (THUNNUS THYNNUS) CAUGHT IN THE CENTRAL MEDITERRANEAN IN 2013 AND 2014

Transcription

1 SCRS/2016/149 Collect. Vol. Sci. Pap. ICCAT, 73(6): (2017) MORPHOMETRIC RELATIONSHIPS OF FATTENING BLUEFIN TUNA (THUNNUS THYNNUS) CAUGHT IN THE CENTRAL MEDITERRANEAN IN 2013 AND 2014 Rafik Zarrad 1 Hechemi Missaoui 2 SUMMARY The present study analyse the length length (LLR) and length weight (LWR) relationships of fattened bluefin tuna (BFT), Thunnus thynnus, caught in the central Mediterranean Sea and famed in the region of Mahdia (Tunisian eastern coasts). Fulton s condition factor (K) was also estimated. A total of 1653 and 713 from the catches of 2013 and 2014, were sampled respectively. The LLRs, the LWRs and the condition factor K showed significant differences between fattened fishes of the two year 2013 and These differences seem related to the period of fattening process. RÉSUMÉ Cette étude analyse les relations longueur-longueur (LLR) et longueur-poids (LWR) du thon rouge Thunnus thynnus, engraissé en Tunisie et pêché en Méditerranée Centrale) en étés 2012 et Le facteur de condition K (Fulton) a été aussi estimé. Au total 1653 (capture 2013) et 713 (capture 2014) poissons engraissés ont été échantillonnés. Les relations LLR et LRW et le facteur de condition K ont montré des différences significatives entre les poissons engraissés de deux années 2013 et Ces différences semblent être liées à la durée d engraissement. RESUMEN Este estudio analiza las relaciones talla-talla (LLR) y talla-peso (LWR) del atún rojo engordado (Thunnus thynnus), capturado en el Mediterráneo central y criado en la región del Mahdia (costas orientales de Túnez) en el verano de 2012 y Se estimó también el factor de condición (K) de Fulton. Se muestrearon en total 1653 y 713 ejemplares de las capturas de 2013 y 2014, respectivamente. Las LLR, LWR y el factor de condición K mostraban diferencias significativas entre los peces engordados durante los dos años, 2013 y Estas diferencias parecen estar relacionadas con la duración del proceso de engorde. KEYWORDS Thunnus thunnus, length-length relationships, length-weight relationships, condition factor 1 Institut National des Sciences et Technologies de la Mer (INSTM-Mahdia), BP 138 Mahdia 5199, rafik.zarrad@instm.rnrt.tn 2 Institut National des Sciences et Technologies de la Mer (INSTM), 28 rue 2 mars 1934 Salammbô. 2188

2 1. Introduction The length weight relationship is widely used in the analysis of fishery data, mostly because of the difficulty and time required to record weight in the field (Andrade and Camos, 2002). The relationship is often used to convert growth-in-length equations for prediction of weight-at-age and use in stock assessment models (Pauly, 1993), to calculate condition indices (Anderson and Gutreuter, 1983). The fattening of Atlantic bluefin tuna (tuna: Thunnus thynnus, Linnaeus, 1758) in Tunisian coasts began commercially in It is known that some morphometric relationships in fish may change as a function of environmental conditions and/or physiological status (Weatherley and Gill, 1987). Therefore, disparity in these relationships on account of fattening process in bluefin tuna is expected. Since growth, feeding, and mobility inevitably differ substantially in wild and fattening conditions, it is also expected that the somatic condition of bluefin tuna will change as a result of the fattening process. This study aims to give information on LLRs, LWRs and on the condition factor for the bluefin tuna caught in the Central Mediterranean and fattened in the east of Tunisia and to compare between two years. 2. Material and methods 2.1 Samples The fattened bluefin tuna were sampled in the tuna farms located in Mahdia (east Tunisia) on board immediately after slaughter. These fishes were captured by purse seine in the Central Mediterranean sea, offshore Tunisian coasts, in June 2013 and June Sampled fishes were 1653 and 713 from the catch of 2013 and 2014, respectively. The fattened specimens were sampled in November-December 2013 and January-February Then fishes were fattened during 5-6 months and 7-8 months. 2.2 Parameters Lengths were measured with a 3-m slide gauge to the nearest centimetre, and weight measured with a digital force gauge to the nearest kilogram. The following parameters were estimated TL: Total Length, FL: Fork Length, CFL: Curved Fork Length, LD1: Head to first Dorsal spine length and TW: Total round Weight. 2.3 Relationships and equations FL of fishes were arranged in the interval of 10 cm to elaborate the size frequencies. The length length relationships (LLR) are described by the equation: L 1 = a + bl 2 L 1 and L 2 : lengths, a and b are constants (intercept and slope, respectively). The length weight relationships (LWR) have the equation: To get the linear equation data were log-transformed, a and b: constants (intercept and slope, respectively). TW = a FL b log(tw) = log a + b log FL The parameters of the LLR and LWR, a and b, the coefficient of determination R² and the standard deviations (S.D.) were estimated by least squares regression and tested by the Student s t test (Zar, 2010). To test the isometric of the relative growth in LLR (b = 1) and LWR (b = 3) the Student s t-test was applied (Sokal and Rohlf, 1995).The significant differences (p = 0.05) of slopes (b) and intercepts (a) of the LLR and LWR between two years was performed by the ANCOVA analysis (Zar, 2010). 2189

3 The Fulton s condition factor (K) was estimated according to the following equation (Froese, 2006): K =10 5 TW / FL 3 where TW: the total round weight in kg of the fish, FL: the fork length in cm. To compare the mean k between two years fattened fishes the Student s t-test was performed (Zar, 2010). Statistical analysis and graphs were performed with STATISTICA Software (Statsoft Inc, version 7.1). 3. Results The FL of 2013 fishes had the minimum of 118 cm and the maximum of 283 cm with an average of cm. The TW was between 36 and 450 kg, with an average of kg (Table 1). FL of 2014 fishes had the minimum of 130 cm and the maximum of 296 cm with an average of cm. The TW was between 44 and 450 kg, with an average of kg. FL length-frequencies for both year show similar distribution patterns with two clusters of fish: small and big. Smaller fish is around the size classes of 140 cm and bigger around for size classes 230 and 240 cm (Figure 1). All LLRs shown in Table 2 were highly significant (test of Student, p< 0.01), with the coefficient of determination values being R²>0.91. For both groups of fishes, the LLRs: FL and TL; FL and CFL showed positive allometry (Table 3). The LLR: FL and LD1 (2014) followed a negative allometry. The ANCOVA showed significant difference between both years (2013 and 2014) for the intercepts (a) and slopes (b) in the LLR (TL = a + b FL and CFL = a + b FL) (Table 4). The LWRs showed a highly significant (t-test, p < 0.001), for both years fattened fishes with the coefficients of determination R² > The calculated coefficient b were for 2013 and for For both years allometry was negative (Table 3). The ANCOVA showed significant difference of the LWR (for intercepts a and slopes b) between the two years (Table 4, Figure 3). Fulton s condition factor (K) in relation to size class is indicated in figure 4. K lower values were 1.31 (class 270 cm) in 2013 and 2.08 (class 170 cm) in The higher condition values of 2013 and 2014 were for the classes 110 cm (K = 2.28) and 180 cm (K = 2.38), respectively. There was a significant difference for the condition factor between the fish caught in 2013 (K = ) and caught in 2014 (K = ) (t-test p< 0.01). 4. Discussion The LLRs, the LWRs and the condition factor K showed significant differences between two years 2013 and 2014 for all relations and the average of K. The three parameters CFL, LD1 and K are known to increase under the influence of the fattened process (Aguado-Gimenez, and García-García, 2005b). The LWRs (W=a FL b ) showed that the b parameters is higher in 2014 than in This seems related to the duration of fattening. Indeed the fattening period of the catch of 2013 was 2 months less than of It s known that the parameters of LWR in fish are affected by a series of factors such as habitat, gonad maturity, sex, feeding and the annual differences in environmental conditions (Froese, 2006). Various authors have also reported differences in the LLW relationships of BFT caught or fattened in the Mediterranean (Table 5). 5. Conclusion In summary, this paper provides basic and updated information on LWRs, LLRs and K for BFT species, caught in the central Mediterranean and fattened in Tunisia useful for fishery biologists and stock assessment. We note the effect, of the duration of fattened process on the different relations and on the condition factor. 2190

4 References Aguado-Gimenez, F. and García-García, B Changes in some morphometric relationships in Atlantic bluefin tuna (Thunnus thynnus thynnus Linnaeus, 1758) as a result of fattening process. Aquaculture 249: Anderson, R.; Gutreuter, S., 1983: Length, weight and associated structural indices. In: Fisheries Techniques, American Fisheries Society. L. Nielsen and D. Johnson (Eds). American Fisheries Society, Bethesda, MA, pp Andrade, H.A.; Camos, R.O., 2002: Allometry coefficient variations of the length weight relationship skipjack tuna (Katsuwonus pelamis) caught in the southwest South Atlantic. Fish. Res. 55, Deguara, S., S. Caruana, C. Agius, An appraisal of the use of length-weight relationships to determine growth in fattened Atlantic bluefin Tuna, Thunnus thynnus L. Collect. Vol. Sci. Pap. ICCAT, 65(3): Froese, R Cube law, condition factor and weight length relationships: history, meta-analysis and recommendations.j. Appl. Ichthyol. 22: Katavic, I., Ticina V. and Franicevic V A preliminary study of the growth rate of bluefin tuna from Adriatic when reared in floating cages. Collect. Vol. Sci. Pap. ICCAT 54(2): Pauly, D., 1993: Fishbyte Section Editorial. ICLARM Quart, Naga. 16, 26p. Percin,F. and Akyol,O.2010.Some morphological relationships in fattened bluefin tuna, Thunnus thynnus L., from the Turkish Aegean Sea. J. Anim. Vet. Adv. 9(11): Sinovcic, G. Franicevic, M. Zorica, B. Cikes-Kec, V Length weight and length length relationships for 10 pelagic fish species from the Adriatic Sea (Croatia). J. Appl. Ichthyol. 20: Sokal, R.R. and Rohlf, F.J Biometry.3 rd Edition, W.H. Freeman and Company, New York, USA 887pp. Tzoumas, A. Ramfos, A. De Metrio, G. Corriero, A. Spinos E., Vavassis, C. and Katselis G Weight growth of Atlantic bluefin tuna (Thunnus thynnus L., 1758) as a results of 6-7 month fattening process in the central Mediterranean. Collect. Vol. Sci. Pap. ICCAT 65(3): Weatherley, A.H. and Gill, H.S The Biology of Fish Growth. Academic Press, London, UK, 443pp. Zar, J.H Biostatistical analysis.5 th Edition Prentice-Hall, New Jerzy. USA 944pp. Zarrad, R., Biometric Relations of wild and fattened Thunnus thynnus (L. 1758) Caught offshore Tunisia (Ionian Sea, central Mediterranean) in Collect. Vol. Sci. Pap. ICCAT 70(1):

5 Table 1. Summary of the observed values for fattened bluefin tuna caught in 2013 and Variable n min mean max SD 2013 TL FL CFL LD TW K TL FL CFL LD TW K Table 2. Parameters of the LLRs and LLWs for fattened bluefin tuna caught in 2013 and 2014 (**: p<0.01). Catch X=FL/ Y= n a b SEa SEb R² p 2013 TL ** CFL ** LD TW ** 2014 TL ** CFL ** LD ** TW ** Table 3. Tests (t-student) of isometric growth for wild and fattened bluefin tuna (p = 0.01). X=FL b SEb tobs Allometry 2013 TL CFL LD1 - - TW TL CFL LD TW = Table 4. Tests (t-student) of comparing of LLRs and LWRs between wild and fattened bluefin tuna (p =0.01). X = FL Intercepts a 1 and a 2 Slopes b 1 and b 2 Y = t a 1 anda t b 1 and b 2 TL CFL TW

6 Table 5. Parameters of LWRs for fattened bluefin tuna from Mediterranean Sea by different authors. Authors a b n Area Sinovcic et al., Adriatic Sea Katavic et al., * Adriatic Sea Aguado-Gimenez, and García-García (2005b) * Balearic Waters Percin and Akyol * Aegean Sea Tzoumas et al., Greece Deguara et al., Malta Zarrad, Tunisia Present work (2013) (2014) * Standardized to cm/g (Froese, 2006), + TW = a TL b Tunisia Number of fish Number of fish FL (cm) LF (cm) Figure 1. Fork length frequency distribution of fattened bluefin tuna, caught in 2013 in the Central Mediterranean. Figure 2. Fork length frequency distribution of fattened bluefin tuna, caught in 2014 in the Central Mediterranean. Figure 3. Relationships between fork length and total weight for fattened bluefin tuna caught in 2013 and 2014 in the Central Mediterranean. 2193

7 Figure 4. Mean condition factor (K) values (±SD) per length class (FL) for bluefin tuna caught in 2013 and 2014 in the Central Mediterranean. 2194