Reproductive Biology of Southwestern Atlantic Wreckfish, Polyprion
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Environmental Biology of Fishes 68: 163–173, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands. Reproductive biology of southwestern Atlantic wreckfish, Polyprion americanus (Teleostei: Polyprionidae) Monicaˆ B. Peresa & Sandro Klippelb aServic¸o da Regiao˜ Litoral, DQA, FEPAM Rua Carlos Chagas 55 sala 707, Centro Porto Alegre, RS 90.030-020, Brazil (e-mail: [email protected]) bTalha-mar Projetos Ambientais, Cons. d’Avila 190 Porto Alegre, RS 91040-450, Brazil Received 5 February 2003 Accepted 12 July 2003 Key words: sexual maturity, fecundity, spawning aggregation, spawning season, migration, deep-sea fish, life-cycle closure, southern Brazil Synopsis We report on the reproductive biology of southwestern Atlantic wreckfish. Females mature first at 77.9 cm total length (TL) (10.4 years) and all are mature by 90 cm TL (15.2 years). Males mature first at 74.9 cm (9 years) and all are mature by 80 cm TL (10.9 years). The wreckfish is a gonochoristic multiple spawner and the gonadal cycle is synchronized at the population level. Spawning occurs from late July to early October along the continental slope (>300 m). Ovarian fecundity varies from 3 to 11.9 million (135–311 oocytes × g−1) and increases exponentially with length. Spawning at western boundary current systems, maintained by homing of adults, is a basic requirement for self-sustaining populations of this species. Introduction are mature and juveniles may live more than 2 years at the sea surface before recruitment to the bottom The wreckfish, Polyprion americanus (Bloch and (Sedberry et al. 1999). Despite its worldwide distri- Schneider, 1801), is a large, long-lived demersal teleost bution and high commercial importance, there is no that inhabits continental and oceanic island slopes of information on reproductive cycle, fecundity, spawn- temperate and subtropical waters of the northern and ing sites and season of these fish. The development southern Atlantic Ocean, Mediterranean, and south- of a method to sample whole fish from commercial ern Indian and southwestern Pacific Ocean (Heemstra landings permitted us to determine: (1) size and age at 1986, Sedberry et al. 1999). Along the southwestern maturity; (2) reproductive cycle; (3) spawning season Atlantic the species occurs from 23◦S, near Rio de and sites; (4) ovarian fecundity (OF); (5) sex ratio. Janeiro – Brazil, to 46◦S in Argentina (Cousseau & Perrota 1998, Peres 2000). The only published study on reproduction (Roberts Materials and methods 1989), reports southwestern Pacific wreckfish as a gonochoristic teleost. In New Zealand bottom trawl The study area was the continental shelf and slope off samples, females attained larger body sizes than males southern Brazil, from 27◦56’S to 34◦49’S (70–590 m and sex ratios were close to 1 : 1. Other related deep). It was divided in two sub-areas, north and south information is that wreckfish eggs and larvae are of Rio Grande (32◦13’S) (Figure 1). Southwestern pelagic (Hardy 1978) and that for southwestern Pacific, Atlantic wreckfish is landed and marketed ice-cooled both Polyprion species undergo a northern spawning and whole, at large body sizes and high prices. Thus, migration (Roberts 1996, Beentjes & Francis 1999). sampling procedures for commercial landings required For North Atlantic stocks, 8–12-year-old wreckfish fast and non-damaging techniques. Fish were measured 164 Figure 1. Study area of wreckfish, P. americanus, divided into two sub-areas off southern Brazil, (N) north and (S) south of Rio Grande. Area of capture of 27 females with hydrated oocytes (grayish) and of eight other, at five fishing sites (full circles), is shown. from the posterior border of the eye orbit to the fork of removed with a surgical curette through the urogeni- the caudal fin (EF in cm) with a flexible metallic tape tal pore (0.1–0.3 ml). This was sufficient to assign sex to the nearest cm. EF was converted to total length (TL and to provide qualitative information of the macro- in cm) by the relationship, TL = 119.5 × EF − 0.0724 scopic aspect of ovarian tissue, registered at dockside. (n = 125; r2 = 0.997; 44–192 cm TL). Sample weights Whenever possible, we preserved an ovary sub-sample were estimated with the total weight–TL relationship (0.5–2 ml) in 2% formalin to assess the frequency dis- TW (kg) = 6.29 × 10−6 × TL3.21 (n = 207; 44–174 cm tribution of oocyte diameters (OD) and their general TL; r2 = 0.98). microscopic aspect (16×). Sub-sampling of immature We determined sex for 641 randomly chosen indi- fish was not possible as gonads are small and tis- viduals, 420 females (74–174 cm TL) and 221 males sues are tightly compacted (n = 82). We removed (73–126 cm TL), by visual examination of sub-samples the left otolith through the opercular opening (420 of the posterior end of the gonads. Sub-samples were females, 221 males and 82 unsexed) and estimated 165 age by opaque band counts of transverse otolith sec- oocytes (YO, 0.6 < OD < 1.4 mm), referred here as tions (Peres 2000). Ice-preserved whole gonads and female OF, for 73 females without hydrated oocytes, lengths of other 114 females (45–174 cm TL) and 86 using the gravimetric method. All YO in a sample of males (44–119 cm TL) were provided by fishers. Addi- 0.2–0.4 g of ovarian tissue, preserved in 10% formalin, tional gonads of 67 females (46–148 cm TL) and 71 were separated from the interstitial tissue, counted and males (44–108 cm TL) were furnished from research extrapolated for preserved whole ovary weight using cruises. Weused exact binomial tests to determine if sex the relationship, OF = n◦YO × (GW/sample weight). ratios differed from the expected 1 : 1. We computed We estimated relative ovary fecundity (ROF) using the ◦ −1 Spearman’s rho coefficient (rs) to determine the corre- relationship: ROF (n YO × g ) = OF/EW. We con- lation between OF and TL. We performed all statistical sidered the presence of hydrated oocytes as evidence analyses in ‘R’ environment (Ihaka & Gentleman of spawning within a few hours (Hunter & Macewicz 1996). 1985) and used this to determine spawning season and Wreckfish gonads may weight up to 4 or 5 kg and spawning sites. We classified adult males by macro- we sampled most of them from commercial catches, scopic visual aspect of the non-preserved testes or after being ice-cooled for 10–25 days. Thus, histolog- by the presence of sperm in gonad sub-sample. We ical sections were of poor quality and were only used classified females by: (1) macroscopic visual aspect to confirm the criteria for gonad staging. We did not of the non-preserved ovarian and oocytes; (2) micro- quantify the atresia rate but its seemed negligible. We scopic general aspect of preserved whole oocytes and, could determine gonad staging in a five-point scale for (3) the microscopic aspect of the histological sections, 462 females (410 adults) (Table 1). Gonad staging for when available. We calculated length at first maturity male wreckfish sub-samples was not possible during (Lm = 50% maturity) by PROBIT regression of adult commercial landings and so we did not assess it in proportion for each length class (5 cm class intervals) this study. We separated ovarian follicles, here called during the active reproductive period. We obtained oocytes, with diameters greater than 0.05 mm, aligned ages at first maturity from the relationship, Age = t0– and measured in a random axis (16×) for 314 female (1/K) × ln (1−(Lm/L∞)), where t0, K and L∞ are the wreckfish (291 adults). For 181 females and 157 males, von Bertalanffy growth model parameters obtained for we used fresh gonad weight (GW in kg) to calculate the females (−6.80 years, 0.054 years−1 and 129.5 cm) gonad-somatic index, GSI = (GW/EW) ×100, where and males (−4.69 years, 0.084 years−1 and 109.5 cm) EW (kg) is the eviscerated somatic weight, estimated wreckfish (Peres 2000). All observed females greater by the relationship EW = 9 × 10−6 × TL3.12 (n = 141; than 90 cm TL were clearly mature. As mature rest- r2 = 0.98). We estimated the total number of yolked ing and immature females are difficult to distinguish, Table 1. Monthly sample sizes and body length ranges (TL in cm) of wreckfish P.americanus, assessed for gonadal stages (GSt), gonad-somatic index (GSI), oocyte diameter distribution (OD) and ovarian fecundity (OF). In the parenthesis is the number of adult fishes examined. Month Female Male GSt GSI OD OF TL GSI TL Jan. 14 (14) — 14 (14) — 91–130 — — Mar. 16 (16) 2 16 (16) — 90–155 3 77–91 Apr. 49 (38) 31 48 (38) 20 55–137 51 58–108 May. 63 (60) 63 59 (58) 27 71–148 26 88–109 Jun. 34 (31) 4 33 (31) 1 79–137 2 73–78 Jul. 105 (100) 22 47 (46) 14 46–137 16 57–112 Aug. 16 (6) 16 11 (6) 6 47–174 35 48–105 Sept. 105 (90) 37 53 (49) 5 48–140 19 56–100 Oct. 37 (36) 2 17 (17) — 87–134 2 72–73 Nov. 4 (0) 4 — — 47–49 2 44–47 Dec. 19 (19) 0 16 (16) — 92–122 1 103 TL 46–174 46–174 55–174 74–174 46–174 44–112 Total 462 (410) 181 314 (291) 73 157 166 monthly GSI analysis included all females greater than pore. OD frequency distribution for each ovarian stage 90 cm TL as adults. shows the sequence of ovary development (Figure 2). Oocyte color, aspect and diameter change with devel- opment (Table 2).