Fishery and Population Characteristics of Euthynnus alletteratus (Rafinesque 1810) in the Eastern Coast of Alexandria, Egypt

Yıl 2013, Cilt: 13 Sayı: 4, - , 01.08.2013

Alaa Eldin El-haweet Essam Sabry Hussain Mohamed

https://doi.org/10.4194/1303-2712-v13_4_08

Öz

Fishery and Population characteristics of Euthynnus alletteratus (Rafinesque 1810) were studied using 695 fishes collected from landing site in Eastern Coast of Mediterranean Sea off Alexandria, Egypt. Eight age groups were recorded using vertebrae. Von Bertalanffy growth parameters were estimated as L∞ = 123.4 cm, K = 0.16 year-1 and t0 = -0.59 year. The rate of total mortality (Z), natural mortality (M) and fishing mortality (F) were 1.996, 0.396 and 1.6 respectively. Length at first capture was estimated as 34cm (1.4 year). The results indicate that population is overexploited (E = 0.802) and suffering from high fishing pressure. Cohort analysis and yield per recruit analysis realized that E. alletteratus stock of the Eastern Coast of Alexandria needs a new management strategy for sustainable yield.

Anahtar Kelimeler

Euthynnus alletteratus, little tunny, Eastern coast of Alexandria, catch, age, mortality, Yield per recruit, management

Kaynakça

• L ∞ K t East Atlantic Spain 115 0.19 -17 Rodriguez-Roda, 1979
• East Atlantic Senegal 5 0.32 Diouf, 1980
• Off Senegalese coast Senegal 112 0.13 Cayré and Diouf, 1983
• Mediterranean Sea Tunisia 111 0.22 Hattour, 1984
• Mediterranean Sea Tunisia 136 0.16 Hattour, 1984
• Mediterranean Sea Turkey 123 0.13 -84 Kahraman and Oray, 2001
• Aegean sea Turkey 128 0.11 -18 Kahraman and Oray, 2001
• West Mediterranean Spain 5 0.39 -0.4 Valeiras et al., 2008
• Coast of Alexandria Egypt 14 0.16 -0.59 Present study Table b value of length weight relationship of E. alletteratus in different area Area b value Author Gibraltar strait 915 Rodriguez-Roda (1966) Tunisia 3 Hattour (1984) Sicily seas 903 Andaloro et al. (1998) Eastern Mediterranean sea, Turkey 726 Kharahman and Oray (2001) Aegean sea, Turkey 697 Kharahman and Oray (2001) Eastern Mediterranean, Turkey 468 Kahraman (2005) Eastern Mediterranean in North Cyprus 956 Kahraman (2005) Levantin basin, Turkey 77 Kahraman and Alicli (2007) Western Mediterranean, Spain 967 Macias (2009) Gulf of Gabes, Tunisia (Sept.) 94 Hajjej et al. (2010) Gulf of Gabes, Tunisia (Dec.) 86 Hajjej et al. (2010) Teboulbah, North Tunisia 82 Hajjej et al. (2011) Zarzis, South Tunisia 91 Hajjej et al. (2011) Alexandria, Egypt 9 Present study spring (Zengin and Karakulak, 2009). Similar seasonal variation between autumn and spring in the present study was recorded, however; the length range was from 13 to 102cm with mean length of 40.7cm, dominated by small size fishes. It is clear that the recorded minimum length (13cm FL) of the little tunny catch is not realistic and the majority of the catch is immature individuals when considering the length at first maturity (40cm FL) for E. alletteratus stock in the present study (unpublished data by present authors). Two methods for natural mortality were estimated, the difference between two estimates are large. In the present study, estimate from Djabali et al. (1994) method which contains asymptotic length as a function of natural mortality was used in calculation. According to Gislason, et al. (2008) the asymptotic length is influence the estimate of natural mortality. Virtual population analysis (VPA) has been widely used in fish stock assessment during the last 30 years (Sparre and Venema, 1998). It is commonly used for studying the dynamics of harvested fish populations. The results in the present study which were obtained from VPA analysis indicate that, the fish which died by natural mortality are higher than those which die by fishing mortality from age group one to five, except for age group 0 which revealed that little tunny in Egyptian Mediterranean Sea water is subjected to a high fishing effort directed to younger fishes negatively affecting its stock.
• Exploitation rate estimate (E cur = 0.8) confirmed the previous conclusion. According to Gulland (1971) the optimum exploitation ratio E opt = 0.5, this implies that the stock of E. alletteratus from Eastern Coast of
• Alexandria is heavily exploited and the fishing pressure exerted in the region is high. The results indicate also that, at the present level of fishing mortality coefficient (F= 1.6), age at first capture (T c = 4 year) and natural mortality coefficient (M= 0.396), the yield per recruit was found to be 702.72g. This means that, the present level of fishing mortality is higher than that which gives the maximum yield per recruit (880.54g). Fishing mortality should be reduced from 1.6 to 0.44 (5%) to achieve this yield per recruit. Moreover, the present level of L c should be raised to at least 44cm for allowing fish to spawn at least one time during its life and increase its biomass. In Turkey, the law disallows catching E. alletteratus less than 45 cm (Zengin and Karakulak, 2009).
• Conclusion It can be concluded that the E. alletteratus stock off the Eastern Alexandria is in a situation of overexploitation and not at sustainable rate, indicating a tendency for catching immature and maturing fishes together. To ensure sustainability of this species, optimum size is required to maximize yield per recruit and allow the stock to recovery through applying management measures including reduction of the present level of fishing effort by about 72.5% and an increase in the length at first capture to reach 44cm. Where reducing of fishing effort seems difficult for socio-economic reasons (low income for artisanal fishery), it is recommended a closed season during late early autumn (September- November) with regulate the mesh sizes of the gill nets used or design an appropriate fishing gear targeted little tunny instead of fishing as bycatch with other target fishes. A new monitoring and control system based on annual data which implements realistic measures with further stock assessment study is urgently needed. References Andaloro, F., Vivono, P., Campagnolo, S., Pipitone, P., Potoschi, A., Mandich, A. and Marino,G. 1998. Biologia e pesca dell'alletterato, Euthynnus alletteratus, (Rafinesque 1910) nei mari siciliani. Biol. Mar. Medit. 5(3): 290–299.
• Belloc, G. 1955. Les thons de la Méditerranée. Deuxième note: Thonine et Bonite. FAO Proc. Gen. Fish. Counc. Medit., 3(52): 471-486.
• Beverton, R. and Holt S. 1957. On the dynamics of exploited fish populations. Fish. Invest. Ser. 11, 19: 533 pp.
• Beverton, R. and Holt, S. 1966. Manual of methods for fish stock assessment. Part 2. Tables of yield functions. FAO Fish. Tech.Pap./FAO Doc. (38) Rev. 1: 67.
• Cadima, L. 2003. Fish stock assessment manual. FAO fisheries technical paper. N0.303.Rome. 161pp.
• Cayré, P. and Diouf, T. 1983. Estimating age and growth of little tunny, Euthynnus alleteratus, off the coast of Senegal, using dorsal fin spine sections. U.S. Department of Commerce, NOAA. Tech. Rep., NMFS, 8: 105–110.
• Chur, V. 1973. On some biological charateristics of little tuna Euthynnus alletteratus Rafinesque, 1810 in the eastern part of tropical Atlantic. Collect. Vol. Sci. Pap. ICCAT, 1:489-500.
• Collette, B. 1986. Scombridae (including Thunnidae, Scomberomoridae, Gasterochismatidae and Sardidae). In: P.J.P. Whitehead, M.-L. Bauchot, J.-C. Hureau, J. Nielsen and E. Tortonese (Eds.), Fishes of the northeastern Atlantic and the Mediterranean, Volume 2. Unesco, Paris: 981-997.
• Diouf, T. 1980. Pêche et biologie de trois Scombridae exploités au Sénégal: Euthynnus alletteratus, Sarda sarda et Scomberomorus tritor. Thèse de doctorat 3ème cycle, Université de Bretagne Occidentale, France, 159 pp.
• Djabali, F., Mehailia A., Koudil, M. and Brahmi, B. 1994. A reassessment of equations for predicting natural mortality in Mediterranean teleosts. NAGA, 17: 33
• Ford, E. 1933. An account of the herring investigation conducted on Plymouth during the years from 1924 – 1933 J. Mar. Biol. Assoc. U.K., 19: 305-384.
• Fromentin, J. and Restrepo, V. 2001. Recruitment variability and environment: issues related to stock assessments of Atlantic Tunas. Col. Vol. Sci. Pap. ICCAT. 52 (5).1780-1792.
• GAFRD. 2008. Annual fishery statistics report. General Authority for Fisheries Resource Development, Ministry of agriculture, Cairo, Egypt.
• Gaykov1, V., Bokhanov, D. 2008. The biological characteristic of Atlantic black skipjack (Euthynnus alletteratus) of the eastern Atlantic ocean. SCRS/2007/132 Collect. Vol. Sci. Pap. ICCAT, 62(5): 1610-1628.
• Gislason, H., Pope, J.G., Rice, J.C. and Daan, N. 2008. Coexistence in North Sea fish communities: implications for growth and natural mortality. – ICES Journal of Marine Science, 65: 514–530.
• Gulland, J. 1971. The Fish Resources of the Ocean. West Byfleet, Surrey, Fishing News (Books) Ltd., for FAO: West Byfleet, Rome, 255 pp.
• Hajjej G., Hattour, A., Allaya, H., Jarboui, O., Mourad, C. and Bouain, A. 2010. Length-weight relationships for 13 species from Gulf of Gabes (Southern Tunisia, Central Mediterranean), 9(37): 6177-6181.
• Hajjej, G., Hattour, A., Allaya, H., Jarboui, O., Mourad, C. and Bouain, A. 2011. Biometry, Length-length and Length-weight relationships of little tunny Euthynnus alletteratus in the Tunisian Waters. Journal of Fisheries and Aquatic Scince, 6(3): 256-263.
• Hattour, A. 1984. Analyse de l’âge, de la croissance et des captures des thons rouges (Thunnus thynnus) et des thonines (Euthynnus alleteratus L.) pêchés dans les eaux tunisiennes. Bull. Inst. Nat. Scient. Tech. Océanogr. Pêche Salammbô, 11: 5–39.
• Hattour, A. 2008. Les thons mineurs tunisiens: étude biologique et pêche. Joint GFCM/ICCAT Expert Meeting on Small Tunas Fisheries in the Mediterranean, Malaga, 200 GFCMICCAT_ ST_008, SCRS/2008/055.
• Johnson, A. 1983. Comparison of Dorsal spines and Vertebraeas ageing structure for little Tunney, Euthynnus alletteratus for the northeast Gulf of Mexico. Summary of round table discussion on age validation. NOAA Tech. Rep. NMFS 8: 111-115.
• Kahraman, A. 1999. Age and growth of Atlantic black skipjack (Euthynnus alletteratus Raf., 1810) in Turkish waters. PhD Thesis, Istanbul University, Institute of Science, Fisheries Program, Istanbul.
• Kahraman, A. 2005. Preliminary investigations on Atlantic little tunny (Euthynnus alletteratus Raf., 1810) in the eastern Mediterranean Sea. Col. Vol. Sci. Pap. ICCAT, 58(2): 502–509.
• Kahraman, A. and Alicli, T. 2007. Sexual maturity of little tunny, Euthynnus alletteratus, in the North-Eastern Levantine Basin. Istanbul University, Fisheries Faculty, Laleli, Istanbul, Turkey. Rapp. Comm. int. Mer Médit., 38 pp.
• Kahraman, A. and Oray I. 2001. The determination of age and growth parameters of Atlantic little tunny (Euthynnus alletteratus Raf., 1810) caught in Turkish waters. SCRS/00/49. Col. Vol. Sci. Pap. ICCAT, 52: 719–732.
• Landau, R. 1965. Determination of Age and Growth Rate in Euthynnus alleteratus and Euthynnus affinis using Vertebrae. Rapports et Procès. Verbaux des Réunions. Publié par les Soins de Jean Furnestin Commission Internationale pour L’Exploration Scientifique de la Mediterranée, XVIII, 16: 241–244.
• Le Cren, E. 1951. The length-weight relationship and seasonal cycle in gonad weight and condition in the perch (Perca u-viatilis). J. Anim. Ecol. 20: 201-219
• Lee, M. 1920. A review of the methods of age and growth determination in fishes by means of scales. Min. Agri. and Fish., Investigations., second series London, 2- 4: (2), 1-32
• Macías, D. 2009. Size distribution of Atlantic little tuna (Euthynnus alletteratus) caught by south western spanish mediterranean traps and recreational trawl fishery. SCRS/2008/189. Collect. Vol. Sci. Pap. ICCAT, 64(7): 2284-2289.
• Pauly, D. 1983. Some simple methods for the assessment of tropical fish stock. FAO Fisheries Technical Paper, 234: 52 pp.
• Pauly, D. 1984. Length- converted catch curves. A powerful tool for fisheries research in the tropics. Part II. ICLARM Fishbyte, 2 (1): 17-19
• Pope, J.G., 1972. An investigation of the accuracy of Virtual Population Analysis using cohort analysis. ICNAF Res. Bull. 9: 65-74.
• Prince E.D. and L.M. Pulos (editors) 1983. Proceeding of the international workshop on age determination of oceanic pelagic fishes: Tunas, bill fish and sharks, NOAA Tech. Rep. NMFS 8, 111-115.
• Rafinesque, C. 1810. Caratteri di alcuni nuovi generi e nuove specie di animali e piante delle Sicilia. San Filippo, Palemo, 106 pp.
• Ramadan Sh., Kheirallah A. and Abdel-salam Kh. 2006. Factors controlling marine fouling in some Alexandria Harbours, Egypt Mediterranean Marine Science. Vol. 7/2: 31-54
• Rodriguez Roda, J. 1966. Estudio de la bacoreta, Euthynnus alletteratus (Raf.), bonito, Sarda sarda (Bloch) y melva Auxis thazard (Lac.), capturados por las almadrabas españolas. Invest. Pesq. 30: 247–92.
• Rodriguez Roda, J. 1979. Edad y crecimiento de la bacoreta, Euthynnus alletteratus (Raf.) de la costa sudatlántica de España. Invest. Pesq. 47 (3): 397–402. Sparre, P. and Venema, S. 1998. Introduction to tropical fish stock assessment. Manual. FAO Fish. Tech. Pap. 306/1, rev. 2, FAO, Rome, 407 pp.
• Sylva, D. and Rathjen W. 1961. Life History Notes on the Little Tuna, Euthynnus alletteratus, from The Southeastern United States. Bull. Mar. Scie. Gulf and Caribbean, volume II.
• Taylor, C. 1960. Temperature, Growth, and Mortality – The Pacific Cockle. J. Cons. int. Explor. Mer. 26(1):1171
• Valeiras, J. and Abad, E. 2007. ICCAT Field Manual. Chapter 2. Description of Species. 2.1 Species Directly Covered by the Convention. 2.2.11. Small tuna.
• Valeiras, X., Macías, D., Gómez, M., Lema, L., Godoy, D., Urbina, J. and Serna, J. 2008. Age and growth of Atlantic little tuna (Euthynnus alletteratus) in the western Mediterranean sea SCRS/2007/140 Collect. Vol. Sci. Pap. ICCAT, 62(5): 1638-1648
• Walford, L. 1946. A new graphic method of describing the growth of animals. Biol. Bull., 90: 141 – 147.
• Wootton, R. 1990. Ecology of teleosts fish. Chapman and Hall, London
• Zengin, M. and Karakulak, F.S. 2009. Preliminary study on the Atlantic black skipjack (Euthynnus alletteratus, Rafinesque, 1810), caught by common purse seine fisheries in the north-eastern Mediterranean coast of Turkey. Coll. Vol. Sci. Pap. ICCAT, 64(7): 221122