SCRS/2004/153
Col. Vol. Sci. Pap. ICCAT, 58(5): 1724-1728 (2005)
LENGTH-WEIGHT RELANTIONSHIPS AND LENGTH-LENGTH CONVERSIONS OF TUNAS AND SWORDFISH IN THE NORTHEAST OF BRAZIL Jorge E. Lins Oliveira1, José A. Vasconcelos2, Paulo Travassos3, José Garcia Jr.1, Juan P. Aldatz1 SUMMARY In the Northeast of Brazil, the capture of tuna and swordfish using monofilament longline is one of the most important economic activities. The purpose of this study was to find out lengthweight relationships and length-length conversions. The tuna and swordfish landings done by national and leasehold fleets between October 2003 and June 2004 were analyzed. Those fleets operate between the latitude 5°00´N and 5°44´S and between the longitude 27°01´W and 36°40´W. The bigeye tuna (Thunnus obesus) contributed with 39,2% of the captures in weight, followed by the yellowfin tuna (Thunnus albacares) with 36% and swordfish (Xiphias gladius) with 23,3%. The albacore (Thunnus alalunga) represented only 1,5% of the captures in weight. The captures done by leasehold fleets showed the greatest average length. For the species that showed the greatest capture (bigeye tuna), the average length was 126 cm fork length (FL), with highest abundance in the classes between 113 and 143 cm (67,9%). There were found weightlength (DWT x OCKL) relationships and conversion equations of length-length (TL x FL; FL x OCKL and TL x OCKL) for some species. RÉSUMÉ Au Nord-Est du Brésil, la pêche des thonidés et de l’espadon à la palangre monofilament représente l’une des principales activités économiques. L’objet de la présente étude est d’identifier les rapports longueur-poids et les conversions longueur-longueur. Les débarquements de thonidés et d’espadon réalisés par les flottilles nationales et en location entre octobre 2003 et juin 2004 ont été analysés. Ces flottilles opèrent entre la latitude 5º00’N et 5º44’S et entre la longitude 27º01’W et 36º40’W. Le thon obèse (Thunnus obesus) a représenté 39,2% des captures en poids, suivi par l’albacore (Thunnus albacares), avec 36% et l’espadon (Xiphias gladius), avec 23,3%. Le germon (Thunnus alalunga) n’a représenté que 1,5% des captures en poids. Les prises réalisées par les flottilles en location contenaient les tailles moyennes les plus grandes. Pour les espèces aux plus fortes captures (thon obèse), la longueur moyenne était de 126 cm longueur à la fourche (FL), avec la plus forte abondance dans les classes entre 113 et 143 cm (67,9%). Des rapports poids-longueur (DWT x OCKL) et des équations de conversion de longueur-longueur (TL x FL ; FL x OCKL et TL x OCKL) ont été identifiés pour certaines espèces. RESUMEN En el Noreste de Brasil, la captura de túnidos y peces espada utilizando el palangre monofilamento es una de las actividades económicas más importantes. La finalidad de este estudio era hallar las relaciones talla-peso y las conversiones talla-talla. Se analizaron los desembarques de túnidos y pez espada realizados por las flotas nacionales y fletadas entre octubre de 2003 y junio de 2004. Dichas flotas operan entre las latitudes 5°00´N y 5°44´S y las longitudes 27°01´W y 36°40´W. El patudo (Thunnus obesus) respondió del 39,2% de las capturas en peso, seguido por el rabil (Thunnus albacares) con el 36% y por el pez espada (Xiphias gladius) con el 23,3%. El atún blanco (Thunnus alalunga) respondió tan sólo del 1,5% de la captura en peso. Las capturas realizadas por las flotas fletadas mostraron las tallas medias más elevadas. Para la especie con mayores capturas (patudo) la talla media fue 126 cm de longitud a horquilla, con mayor abundancia de las clases entre 113 y 143 cm (67,9%). Se 1
Universidade Federal do Rio Grande do Norte (UFRN), Praia de Mãe Luiza, s/n, 59014-100 Natal/RN, Brasil.
[email protected] Instituto Brasileiro de Meio Ambiente (IBAMA/RN), Rua Alexandrino de Alencar, 1399, 59015-350 Natal/RN, Brasil. 3 Universidade Federal Rural de Pernambuco (UFRPE), Rua Dom Manoel de Medeiros, s/n, 52171-900 Recife/PE, Brasil 2
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hallaron relaciones peso-talla (DWT x OCKL) y ecuaciones de conversión talla-talla (TL x FL; FL x OCKL y TL x OCKL) para algunas especies. KEYWORDS Northeast Brazil, Tunas, Billfish, Length-weigth relantionships, Length-length conversions 1. Introduction Nowadays, the tuna fishery in the Northeast of Brazil is one of the main economic activities. The most important port is based in Natal, Rio Grande do Norte, where national and leasehold tuna’s boats are gathered under lease. The tuna fishing fleet that operated in 2003 was formed by 37 leasehold boats, being 29 from China, 8 from other nations (Japan, North America, Panama, Bolivia and Canada) and 33 from the national boats (IBAMA 2004). Since 1996, with the beginning of the leasing agreement for boats using longline monofilament, tuna and swordfish production in the Northeast of Brazil showed a significant growth. However, with an increase of 95% in the number of tuna boats from 1999 to 2000, going from 39 to 55 national boats and 27 to 74 leasehold boats, the captures went from 10.971,5 t in 1999 to 20.773,2 t, in 2001 (Hazin et al. 2004; IBAMA 2004, ValeEvangelista et al. 1998). After this period, the most fished species was the albacore (Thunnus alalunga) and the bigeye (Thunnus obesus), that contributes with around 50% of the total production in 2001. According to Hazin et al. (2004), this fact is associated to the increase of Chinese boats that capture albacore, and the end of fishing activities of the Spanish boats that had swordfish as a target species. However, information about capture composition, length-weight relationships and length-length conversions of tunas and swordfishes captured in the Northeast of Brazil are still very scarce (Goes et al. 2002; Lima et al. 2002). This information is important to the analysis of the structures of the populations of these captured species, as well as to direct plans of management of the fishery activity. With the objective of contributing with information for a better agreement about tuna and swordfish fishery in the northeast region, this study shows the capture and some biometrical relationships for the highly captured species by tuna fleets using longline. 2. Material and methods Since October 2003 to June 2004 tuna and swordfish landings done by the national and leasehold fleets that operate along the northeast coast of Brazil, between the latitude 5°00´N and 5°44´S and between the longitude 27°01´W and 36°40´W were observed. This study is part of the project named “Compilation and analysis of Brazilian data regarding tuna capture”, done with financial resources from the Special Secretariat of Aquaculture and Fishing in partnership with the IBAMA (Brazilian Institute of Environment) and universities of the northeast of Brazil. Both fleets (national and leasehold), use longline to capture tuna and swordfish, with the following characteristics: 40 to 55 nautical miles of monofilament nylon of 4 mm of diameter, the secondary lines of 6mm with 15 meters length without steel whip, light-stick connected next to the hook 9/0 size, using a squid as bait. The average depth of capture, that varies from 40 to 50 meters. A total of 4.818 specimens have been analyzed. The biometry of the tunas consisted in the attainment of the Total Length (from the tip of the snout until the edge of the caudal fin-TL), the fork length (from the tip of the snout until the fork-FL) and the operculum-caudal keel length (from the distal edge of the operculum until the tip of the caudal keel-OCKL). This measure is the principal length obtained during the landings, because the specimens arrive gilled, gutted, without part of the head and fins. For swordfish the measured lengths had been: the edge of the lower jaw until the fork (LJFL), and the operculum-caudal keel length. For all specimens the dressed weight (DWT) was gotten.
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3. Results and discussion Considering the data of landings done by national and leasehold boats, the bigeye tuna contributed with 39,2% of the captures in weight, followed by the yellowfin tuna with 36% and swordfish with 23,3%. During the study the albacore only represented 1,5% of the captures in weight. The minimum, average and maximum FL of the species captured by the national (NF) and leasehold (LF) fleet. For yellowfin tuna, the specimen’s average length captured by leasehold fleet showed a higher average length (137 cm), than the specimens captured by the national fleet. It can be inferred that this fact is related to the different strategies of capture, as well as a better autonomy of these boats, that allow them to access other fishing areas. For the bigeye, the average length of the specimens captured by both fleets was the same, oscillating from 125 to 127 cm. For the albacore, only the national fleet showed significant captures. The average length of the captured specimens was 107 cm. The swordfish captured by both fleets did not presented great differences in relation to the specimens´ average length, oscillating from 162 to 166 cm (Table 1). For the yellowfin tuna captures it was observed that the leasehold fleet captured bigger specimens in comparison with the national fleet, being the 118 to 153 cm FL. The classes that showed the biggest captures for the leasehold fleet (71,5%). The national fleet showed FL classes with higher occurrence of capture going from 108 to 143 cm (59%) (Figure 1). For the bigeye tuna, the length classes that presented the greater captures did not changed significantly. For the leasehold fleet, the higher number of specimens was captured in the classes: 118 to 143 cm FL (58,5%). The greater captures done by the national fleet were concentrated in the same classes also (62,4%) (Figure 2). For the swordfish, the specimens captured were concentrated between the 140 and 190 cm classes, both for the leasehold (80,4%), and national fleets(75,3%) (Figure 3). Length-weight relationships and length-length conversions for the species captured in the Northeast of Brazil are presented in Table 2. These relations are important to rebuild the tuna capture in length based by the weight, as well as to convert all measures using the same pattern used by the ICCAT allowing that capture data of tuna and similar in northeast of Brazil to be added to the international data bank.
4. References GÓES, C.A., M.S.P. Lima, J.E. Lins Oliveira and J.A. Oliveira Neto. 2002. Aspectos populacionais da Albacora Lage (Thunnus albacares) capturado pela frota industrial do Rio Grande do Norte. Anais do XXIV Congresso Brasileiro de Zoologia, Itajai – SC. 267p. HAZIN, F.H.V., P. Travassos and J.E. Lins Oliveira. 2004 (in press). Dinâmica pesqueira dos principais estoques explorados no Nordeste do Brasil/REVIZEE-NE. IBAMA. 2004. Boletim Estatístico da Pesca Marítima e Estuarina do Nordeste do Brasil – 1996/2003. 105p. LIMA, M.S.P., C.A. Góes, J.E. Lins Oliveira and J.A. Oliveira Neto. 2002. Relações morfométricas do Thunnus obesus capturado pela frota industrial do Rio Grande do Norte. Anais do XXIV Congresso Brasileiro de Zoologia, Itajai – SC. 268p. VALE-EVANGELISTA, J.E., G.M. Oliveria and J.A. Vasconcelos. 1998. Evolução da pesca de atuns no Nordeste do Brasil. Boletim Técnico-Científico do CEPENE 6(1): 77-108.
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Table 1. Minimum, average and maximum Fork Length (FL) for tunas and Lower Jaw Fork Length (LJFL) for swordfish caught in the Northeast of Brazil. Species
minimum (cm) NF LF Yellowfin tuna 63 82 Bigeye tuna 73 81 Albacore 95 * Swordfish 70 124 * The captures were insignificant.
average (cm) NF LF 125 137 125 127 107 * 162 166
maximum (cm) NF LF 186 211 170 179 123 * 293 265
n NF 1193 984 118 620
LF 677 776 * 450
Table 2. Length-weight relationships and length-length conversions for the species caught in the northeast of Brazil. Specie Yellowfin tuna
Bigeye tuna
Swordfish
Relations
R²
n
2,7859
DWT = 0,0002*OCKL
0,922
1.870
TL/FL
TL = (1,0309*FL) + 8,1684
0,989
1.142
FL/OCKL
FL = (1,4689*OCKL ) + 14,307
0,906
1.142
TL/OCKL
TL = (1,5256*OCKL) + 22,584
DWT/OCKL
0,925
1.142
2,6205
DWT = 0,0004*OCKL
0,867
1.760
TL/FL
TL = (1,0455* FL) + 6,5839
0,976
270
FL/OCKL
FL = (1,541*OCKL) + 8,2069
0,891
270
TL/OCKL
TL = (1,6273*OCKL) + 13,951
0,887
270
0,865
1070
0,876
734
0,823
118
DWT/OCKL
DWT/OCKL LJFL/OCKL
Albacore
Equations
DWT/OCKL
2,8669
DWT = 0,00008*OCKL
LJFL = (1,452* OCKL) + 26,868 2,2352
DWT = 0,0021*OCKL
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Figure 1. Length distribution for the yellowfin tuna caught by the national and leasehold fleet.
Figure 2. Length distribution for the bigeye tuna caught by the national and leasehold fleet.
Figure 3. Length distribution for the swordfish caught by the national and leasehold fleet.
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