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SCRS/2004/125 Col. Vol. Sci. Pap. ICCAT, 58(3): 1179-1187 (2005)

SYNOPSIS OF BIOLOGICAL INFORMATION AVAILABLE ON BLUE , PRIONACE GLAUCA, FROM THE SOUTHWESTERN ATLANTIC OCEAN

Fábio Hazin and Rosângela Lessa

SUMMARY

This document presents a synopsis of the available fishery and biological information for blue shark caught off Brazil. Fishery information in terms of distribution of the catches by the longline fleet and in terms of trends in CPUE are presented. In addition, the document provides information on reproductive biology and growth. Based on the estimated growth rates and catches, estimates of total mortality are provided.

RÉSUMÉ

Ce document présente un résumé des informations disponibles sur les pêches et la biologie pour le requin peau bleue capturé au Brésil. Les informations sur les pêches en termes de distribution des prises réalisées par la flottille palangrière et en termes de tendances de la CPUE y sont présentées. En outre, le document fournit des informations sur la biologie de la reproduction et la croissance. En se basant sur les taux de croissance et les prises estimés, des estimations de la mortalité totale sont soumises.

RESUMEN

Este documento presenta una sinopsis de la información disponible sobre biología y pesquerías para la tintorera capturada en las aguas de Brasil. Se presenta información en términos de distribución de las capturas realizadas por la flota palangrera y en términos de tendencias en la CPUE. Además, el documento presenta información sobre biología reproductiva y crecimiento. Basándose en las tasas de crecimiento y en las capturas, también se proporcionan estimaciones de mortalidad total.

1179 1. Distribution and relative abundance

The blue shark, Prionace glauca, is a pelagic oceanic , with a worldwide distribution in temperate and tropical waters. With the widest geographic distribution among all large , it is the most abundant elasmobranch in longline catches in oceanic areas. It is a common species throughout Brazilian coast, being frequently caught by the longline fishery for and swordfish. Blue shark catches have always been kept by Brazilian vessels operating from Santos and Natal, whilst been commonly discarded by chartered vessels, after finning. Although this practice has been banned in Brazil since August 24, 1998, it is suspected to have continued at unknown levels. Therefore, in order to evaluate trends in CPUE along time only data from Brazilian vessels can be used.

Data from Santos indicate that blue shark CPUE was very low from 1971 to 1974, increasing then gradually up to 1985, when, for the first time, it reached a value close to 10 (9.87) (Figure 1). After that year on, it fluctuated from about 8 to 10, in a relatively stable way. The rise in CPUE from 75 to 85 reflected a gradual increase in price of and fins, which resulted, after 1985 on, in its inclusion as a target species, together with tunas and swordfish. After that happened, CPUE remained relatively stable.

The blue shark CPUE of the Brazilian fleet based in Natal has been, in general, about one third of the values obtained off southeast Brazil, confirming the increase in the abundance of the species with latitude. From 1983 to 1986, tunas were the target species, accounting for most of the catches and sharks were not recorded by species. In 1986, sharks, mainly the blue shark, also became a target, resulting in an increase of their CPUE, up to 1988, when it peaked at 6.26. From that year on, up to 1991, the catch of tunas rose again due to the discovery of new fishing grounds around the Archipelago of Saint Peter and Saint Paul. As a consequence, blue shark CPUE dropped by almost half, remaining close to 4.00. In 1991, the finding of important concentrations of sharks of the genus , mainly the , C. signatus, over seamounts off northeast Brazil (Hazin et al. 1998), prompted a dislocation of the fishing effort to those areas, resulting in an increase of their catches and a further decline of blue shark CPUE, which stabilized then at around 1.50. In the middle nineties, through the chartering of foreign vessels, new fishing technologies, aimed at higher catches of swordfish, were incorporated by the Brazilian fleet, including the use of monofilament poliamid longlines, together with light sticks and as bait. As a result, swordfish CPUE increased by about 6 times, while blue shark CPUE doubled, fluctuating then, from 1995 to 2000, at around 3.00.

The several changes of blue shark CPUE along the years, from both Natal and Santos fleet, seem to be strongly related to the changes of target species, being relatively stable, though, during the periods of time when the target species has remained the same.

CPUE of mako sharks, in turn, was much lower than those of blue shark, about ten times less, being also much higher off southern Brazil, than off northeast. Due to their low values, trends in abundance are difficult to assess. Nevertheless, CPUE of the fleet from Santos has been relatively stable since the beginning of the fishery, ranging from about 0.60 to 1.20.

Further information on blue shark distribution and relative abundance off Brazil can be found in Hazin et al., 1990; Hazin et al. 1994; and Hazin et al. 1998.

2. Reproductive biology

Blue shark copulates off southeast Brazil, mainly from December to February (Amorim 1992), whilst ovulation and fertilization occur off northeast Brazil, about three to four months later, mainly from April to June. This is the time of the year with highest sea surface temperature and females seem to be sexually segregated from males, being distributed in shallower and warmer waters, possibly to facilitate the process of ovulation, fertilization and early development of their embryos (Hazin et al. 1994). Inseminated females store spermatozoa in their oviducal glands. The highest catches of female blue sharks off southeast happen during the fourth and first quarters, whereas off northeast they occur during the first and second quarters. The size range of female blue sharks in both areas is also similar, roughly from 200 to 270 cm TL.

The available data suggest that female blue sharks would be moving from off southeast Brazil, where copulation occurs, to off northeast Brazil, where ovulation takes place, and from there to the Gulf of Guinea, where females in early pregnancy are found from June to August (Castro and Mejuto 1995). The parturition area is not possible to guess from the present information, but based on the data available from other Oceans (Nakano 1990), it would probably be located from the south coast of Africa, where upwelling occurs, to the subtropical convergence (Figure 3) (Hazin et al. 2000).

1180 Female sexual maturity is reached at about 228 cm TL. Ovarian fecundity is about 30 and females are ready for a new ovulation and pregnancy close after parturition. Gestation takes about 9 to 10 months. Although embryos occur at the same relative stage of development, completely distinct developmental stages may also happen, occasionally.

Males attain sexual maturity at about 225 cm TL and show a seasonal fluctuation of sperm production. Further information on blue shark reproductive biology in the southwestern Atlantic is available in Hazin et al. 1994, and Hazin et al. 2000.

3. Age, growth and population structure

Total length ranged from 173.8 cm to 310.0 cm TL, for males, and from 185.5 to 283.0 cm TL for females (Figure 4). Sex ratio was favorable to females; 1.81:1.00. The length weight relationship was established to estimate a and b parameters of the function EW= aTLb for both sexes together: EW=0.010TL2.8592 (r2= 0.85), where EW= Eviscerated weight, and TL= Total length (Figure 5).

Cleaned vertebrae fixed in 4% formaldehyde (24 to 48 hours) were preserved in 70% alcohol. Each one was embedded in polyester resin and sectioned approximately 1 mm thick containing the nucleus using a low speed saw. Readings were carried out according to procedures described by Cailliet (1983).

The von Bertalanffy (1938) growth model parameters were fit to a) observed lengths at age; b) mean back- calculated lengths; c) observed lengths combined to back-calculated lengths. Observed lengths provided the best -1 fit. Growth parameters were: L∞ = 352.1 cm TL; K = 0.1571 year ; and t0 = -1,01year (Figure 6).

Growth parameters were also derived using the Richards function and the Schnute function, but the von Bertalanffy was found to best fit the data (Lessa et al. 2004). The estimated size at first maturity for males (225 cm TL) and females (228 cm TL) (Hazin 1991), corresponded to age 5 in both sexes. The oldest specimen in the sample, 310 cm TL, corresponded to a 12 years-old specimen.

To locate periodic trends in band formation, monthly mean marginal increments MI ± SD were calculated, and then tested for normality and for significant differences using analysis of variance (ANOVA). The mean MI for groups 3 to 5 and for the overall sample reaches the minimum in December/January. Some band formation seems to occur throughout the entire period. Differences in MI were significant for most age groups. However, for 6 to 8 years, although a decreasing trend is observed in the same period as for other age groups, significant differences were not detected. The results indicate an annual pattern of deposition, as it has been assumed by several authors (Stevens 1975; Cailliet et al. 1983; Skomal & Natanson 2003) (Figure 7). Age ranged from 3 to 12 for males and from 4 to 9 for females, with modal classes in age groups of 5 and 7 years, respectively (Figure 8). The onset of sexual maturity occurs from 5 years, and adult specimens accounted in landings for 86.5%.

Mortality rates, exploitation rate and survival estimated through the catch curve were: Z = 0.65 year-1; M= 0.26 year-1; F= 0.23 year-1; E= 0.60 year-1 and S= 52.4 % (Figure 9).

Differences between equilibrium and the actual mortality for the species off Brazil were estimated through the percentage of survival (lx) and the prognostic of the age composition in the population (Cx). Such analysis reveals that if the population were in equilibrium, individuals would attain 11 years-old. However, current values indicate that the generation is extinct at 8 years (Figure 10).

Although the estimated mortality rate indicates that fishing is being compensated by population increase (Z’ > Z), an unknown amount of specimens discarded by “finning” has not been taken into account, suggesting that mortalities may be strongly biased since they were estimated from landings. The small amount of juveniles in the whole sample may also contribute to distortions in mortality estimations.

Although the estimated exploitation rate obtained (0.6) is high, in relation to the abundance in longline catches, demographic analyses do not indicate overfishing. Two main reasons, related to the age at maturity and fecundity, may explain such a result (Smith et al. 1998; Silva 2001). The more precocious the maturity is, the higher will be the number of individuals in the population. Besides, a high fecundity, as for the blue shark, will increase the population in numbers. Furthermore, the blue shark shows a sexual maturity that coincides with recruitment to fisheries. These reasons may explain why the high exploitation rate seems to be compensated by the intrinsic populational increase rate r. Finally, it is important to note that since these results were based on samples obtained from 1992 to 2000, they should be interpreted with caution. New data collection is strongly recommended in order to update these analyses.

1181 4. Literature cited

AMORIM, Alberto F. 1992. Estudo da biologia, pesca e reprodução do cação azul, Prionace glauca L. 1758, capturado no sudeste e sul do Brasil. Ph.D. Thesis, Universidade Estadual Paulista, Rio Claro, São Paulo. Brazil, 176 p.

BERTALANFFY, L. von. 1938. A quantitative theory of organic growth (inquiry on growth laws). Hum. Biol. 10:181-318.

CAILLIET, G.M., L.K. Martin, D. Kusher, P. Wolf & B.A. Welden. 1983. Preliminary studies on the age and growth of the blue, Prionace glauca, common thresher, Alopias vulpinus, and short mako, oxyrinchus, sharks from California waters. In: Prince, E.D., Pulos, L.M. (Ed.), Proceedings of the International Workshop on Age Determination of Oceanic Pelagic : Tunas, Billfishes, and Sharks. NOAA Tech. Rep. NMFS 8, 179-188.

CASTRO, J.A. and J. Mejuto. 1995. Reproductive parameters of blue shark, Prionace glauca, and other sharks in the Gulf of Guinea. Mar. Freshwater Res., 46:967-973.

LESSA, R.P.T., F.M. Santana, and F.H.V Hazin. 2004. Age and growth of the blue shark Prionace glauca (Linnaeus, 1758) off northeastern Brazil. Fisheries Research, 66:19-30.

HAZIN, Fábio H.V. 1991. Ecology of the blue shark, Prionace glauca, in the southwestern equatorial Atlantic. M.Sc. Dissert. Tokyo University of Fisheries, 123 pp.

HAZIN, Fábio H.V., P.B. Pinheiro, M.K. Broadhurst. 2000. Further notes on reproduction of the blue shark, Prionace glauca, and a postulated migratory pattern in the South Atlantic Ocean. Ciência e Cultura, v.52, n.2, p.114-120.

HAZIN, Fábio H.V., J.R. Zagaglia, M.K. Broadhurst, P.E.P. Travassos, T.R.Q. Bezerra. 1998. Review of a small-scale pelagic longline fishery off northeastern Brazil. Marine Fisheries Review, 60(3):1-8.

HAZIN, Fábio H.V., C.E. Boeckmann, E.C. Leal, R.P.T. Lessa, K. Kihara, K. Otsuka. 1994. Distribution and relative abundance of the blue shark, Prionace glauca, in the southwestern equatorial Atlantic Ocean. Fishery Bulletin, U.S. . Wildl. Serv., v.92, p.474-480.

HAZIN, Fábio H.V., R.P.T. Lessa, M. Chammas. 1994. First observations on stomach contents of the blue shark, Prionace glauca, from southwestern equatorial Atlantic Ocean. Anais da Academia Brasileira de Ciências, Academia Brasileira de Ciência, v.54, n.2, p.195-198.

HAZIN, Fábio H.V., C.E. Boeckmann, E.C. Leal, K. Otsuka, K. Kihara. 1994. Reproduction of the blue shark, Prionace glauca, in the southwestern equatorial Atlantic Ocean. Fisheries Science, v.60, n.05, p.487-491.

HAZIN, Fábio H.V., A.A. Couto, K. Kihara, K. Otsuka, and M. Ishino. 1990. Distribution and abundance of pelagic sharks in the south-western equatorial Atlantic. J. Tokyo Univ. Fish., 77(1):51-64.

NAKANO, H. Ecological study on age, breeding and migration of blue shark from the North Pacific Ocean. 1990. D.Sc. Thesis, Hokkaido University.

SILVA, F. M.S. 2001. Taxas de crescimento populacional intrínseco de tubarões: uma contribuição para o plano de manejo de elasmobrânquios no Brasil. Dissertação de mestrado doe Oceanografia Biológica da Universidade Federal de Pernambuco. 75p.

SKOMAL, G.B. & L.J. Natanson. 2003. Age and growth of the blue shark (Prionace glauca) in the North Atlantic Ocean. Fishery Bulletin, 101: 627-639.

SMITH, S. E., D.W Au,, E.C. Show. 1998 Show Intrinsic rebound potentials of 26 species of Pacific sharks. Marine and Freshwater Research, 49: 663-678.

STEVENS, J.D. 1975. Vertebral rings as a means of age determination in the blue shark (Prionace glauca L.). J. Mar. Biol. Assoc. U. K. 55, 657-665.

1182 12 10 8 6 4 2 CPUE (n/ 1000 hooks) CPUE 0 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 Year

Santos Natal

Figure 1. Yearly catch per unit of effort (number of fish per 1,000 hooks), for the blue shark, from Brazilian longliners operating from Santos (1971 to 1995) and Natal (1986 to 2002).

2 1,8 1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 CPUE (n/ hooks) 1000 CPUE 0 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 Year

Santos Natal

Figure 2. Yearly catch per unit of effort (number of fish per 1,000 hooks), for the mako shark, from Brazilian longliners operating from Santos (1971 to 1995) and Natal (1986 to 2002).

1183

Figure 3. Theorized movements by female blue sharks in the South Atlantic Ocean (after Hazin et al. 2000).

Figure 4. Length-frequency distribution of male (n= 410) and female (n= 225) blue sharks, off northeast Brazil.

1184

70000 PE = 0,0101CT2,8591 2 60000 r = 0,85 50000

40000

30000 20000

Peso eviscerado (g) 10000 0 0 50 100 150 200 250 300

Comprimento total (cm)

Figure 5. Relationship between eviscerated weight and total length for blue shark, with sex combined.

350

300

250

200 150 100 50

(cm) total Comprimento 0 02468101214 Idade (anos) Figure 6. Von Bertalanffy Growth curve for both sexes of blue shark, off northeast Brazil.

1,0 0,9

0,8 19 49 0,7 12 48 23 5 11 16 27 0,6 0,5 8 IMM 6 0,4 11 0,3 0,2 0,1 0,0 JFMAMJJASOND

Meses

Figure 7. Mean vertebral marginal increment (MI), by month, for the blue shark off northeast Brazil.

1185

30 45 40 Fêmeas 25 35 Machos ) ) % 20 % 30 ( ( 25 15

üência üência 20 üência üência q q 10 15 Fre Fre 10 5 5 0 0 01234567891011121314 01234567891011121314 a Idade (anos) b Idade (anos)

Figure 8. Age distribution of blue sharks caught off northeast Brazil for both sexes combined (left) and separated by sex (right).

.

8 ln (N)= -0,67 Idade + 10,13

6

4 ln(N)

2

0 0 5 10 15 Idade relativa (anos)

Figure 9. Catch curve of blue shark off northeast Brazil.

1186 Equilíbrio Real Equilíbrio Real

120 0,6 100 0,5 80 0,4 60 Cx 0,3 40 0,2 20 0,1

lx (no. de sobreviventes) lx 0 0,0 01234567891011 01234567891011 Idade (anos) Idade (anos)

Figure 10. Percentage of survival and prognostic of age composition of the population for equilibrium and actual mortality rates.

1187