Fábio H. V. Hazin

Age and growth of the blue shark Prionace glauca (Linnaeus, 1758) off northeastern Brazil

Between 1992 and 2000, 681 blue sharks, Prionace glauca(173.8–310 cm total length, TL) were collected off northeastern Brazil (Brazilian EEZ). Vertebral sections of 156 males (173.8–310 cm TL) and 80 females (185.5–283 cm TL) were analysed. The index of average percentage error (IAPE) ranged from 0 to 3.1% for 3–12 growth rings (GRs). Mean marginal increment (MI) decreased from November to January without, however, conclusively confirm the annual pattern of deposition. Growth parameters were derived using the von Bertalanffy growth function (VBGF), the Richards function and the Schnute function. VBGF was that which best fit the data. Parameters derived from back-calculated lengths, K = 0.157, L∞ = 352.1 cm and t0 =− 1.01 year, were considered to best describe growth. First maturity sizes of 225 cm for males and 228 cm for females corresponded to 5-GRs individuals. A 310-cm male had 12 GRs which was the highest number in the entire sample. Growth rates of 33.9 cm per GR were estimated from birth to the first band corresponding to 60.2% of size at birth, which is 56.4 cm. Adult males were 90.5% of the entire male sample and, adult females corresponded to 79.6% of the sample of females. The male sample was composed of individuals from 3 to >11 GRs and females were 3 to 10 GRs. Males were larger (with higher number of GRs) and outnumbered females in the overall sample, as commonly occurs in catches worldwide. Despite the hypothesis of differential growth by sex, postulated by several authors, the present study demonstrated that growth curves did not differ significantly, even considering significant vertebral radius (VR)–TL regressions for males and females. Higher growth rates were found in the southern Hemisphere, leading to significant differences in VBGF when compared to other areas. Discards and unreported catches are of great concern for conservation of this important apex predator.

Aspects of reproductive biology of the scalloped hammerhead shark, Sphyrna lewini, off northeastern Brazil

Ninety four scalloped hammerhead sharks, Sphyrna lewini (53 females and 41 males) ranging in size from 121 to 321 cm total length (TL), were collected from surface gillnetters operating off northeastern Brazil and throughout the southwestern equatorial Atlantic Ocean between January and December 1996. A common regression for TL and eviscerated weight (EW) was calculated as, log EW = −11.786 + 2.889 log TL. Females and males were categorised into reproductive stages (4 and 2, respectively) according to morphological changes in their gonads. Size at sexual maturity for females was estimated to be 240 cm, while males appeared to mature at between 180 and 200 cm. Gravid females had between 2 and 21 embryos or pups, varying in TL from 3 to 38 cm. There was no relationship between maternal length and size of litter. Copulation and parturition appear to occur outside the sampled area and possibly closer to the coast. With the exception of slightly lower uterine and ovarian fecundities, the results support the few existing data on the reproductive cycle of S. lewini in other areas.

Influences of type and orientation of bait on catches of swordfish (Xiphias gladius) and other species in an artisanal sub-surface longline fishery off northeastern Brazil

Two experiments were done to examine the relative effectiveness of squid and mackerel as bait for artisanal longliners operating off the northeast coast of Brazil. In experiment 1, compared to clusters of hooks baited with vertically orientated squid, those with vertically orientated mackerel (attached to hooks according to normal commercial operations) showed significantly more contact by fish and had less bait remaining at the end of each set, but retained significantly less total fish by weight and fewer swordfish. Significantly more swordfish swallowed hooks baited with vertically orientated squid, than those with vertically orientated mackerel and showed greater mortality. In experiment 2, clusters of hooks baited with horizontally orientated mackerel had significantly greater contact by fish and less bait remaining than those baited with vertically orientated squid. No other significant differences were detected between baits. Type of bait showed no significant effect on anatomical hook location and mortality for total catch (all species combined) and swordfish. The results are discussed in terms of possible factors influencing behaviour of fish during the hooking process and the importance of the visual stimuli of baits for sub-surface longlines.

Vertical Movement Patterns and Ontogenetic Niche Expansion in the Tiger Shark, Galeocerdo cuvier

Sharks are top predators in many marine ecosystems and can impact community dynamics, yet many shark populations are undergoing severe declines primarily due to overfishing. Obtaining species-specific knowledge on shark spatial ecology is important to implement adequate management strategies for the effective conservation of these taxa. This is particularly relevant concerning highly-mobile species that use wide home ranges comprising coastal and oceanic habitats, such as tiger sharks, Galeocerdo cuvier. We deployed satellite tags in 20 juvenile tiger sharks off northeastern Brazil to assess the effect of intrinsic and extrinsic factors on depth and temperature usage. Sharks were tracked for a total of 1184 d and used waters up to 1112 m in depth. The minimum temperature recorded equaled 4°C. All sharks had a clear preference for surface (< 5 m) waters but variability in depth usage was observed as some sharks used mostly shallow (< 60 m) waters whereas others made frequent incursions into greater depths. A diel behavioral shift was detected, with sharks spending considerably more time in surface (< 10 m) waters during the night. Moreover, a clear ontogenetic expansion in the vertical range of tiger shark habitat was observed, with generalized linear models estimating a ~4-fold increase in maximum diving depth from 150- to 300-cm size-classes. The time spent in the upper 5 m of the water column did not vary ontogenetically but shark size was the most important factor explaining the utilization of deeper water layers. Young-of-the-year tiger sharks seem to associate with shallow, neritic habitats but they progressively move into deeper oceanic habitats as they grow larger. Such an early plasticity in habitat use could endow tiger sharks with access to previously unavailable prey, thus contributing to a wider ecological niche.

Regional movements of the tiger shark, Galeocerdo cuvier, off northeastern Brazil: inferences regarding shark attack hazard

An abnormally high shark attack rate verified off Recife could be related to migratory behavior of tiger sharks. This situation started after the construction of the Suape port to the south of Recife. A previous study suggested that attacking sharks could be following northward currents and that they were being attracted shoreward by approaching vessels. In this scenario, such northward movement pattern could imply a higher probability of sharks accessing the littoral area of Recife after leaving Suape. Pop-up satellite archival tags were deployed on five tiger sharks caught off Recife to assess their movement patterns off northeastern Brazil. All tags transmitted from northward latitudes after 7-74 days of freedom. The shorter, soak distance between deployment and pop-up locations ranged between 33-209 km and implied minimum average speeds of 0.02-0.98 km.h-1. Both pop-up locations and depth data suggest that tiger shark movements were conducted mostly over the continental shelf. The smaller sharks moved to deeper waters within 24 hours after releasing, but they assumed a shallower (< 50 m) vertical distribution for most of the monitoring period. While presenting the first data on tiger shark movements in the South Atlantic, this study also adds new information for the reasoning of the high shark attack rate verified in this region.

High connectivity of the crocodile shark between the Atlantic and Southwest Indian Oceans: highlights for conservation.

Among the various shark species that are captured as bycatch in commercial fishing operations, the group of pelagic sharks is still one of the least studied and known. Within those, the crocodile shark, Pseudocarcharias kamoharai, a small-sized lamnid shark, is occasionally caught by longline vessels in certain regions of the tropical oceans worldwide. However, the population dynamics of this species, as well as the impact of fishing mortality on its stocks, are still unknown, with the crocodile shark currently one of the least studied of all pelagic sharks. Given this, the present study aimed to assess the population structure of P. kamoharai in several regions of the Atlantic and Indian Oceans using genetic molecular markers. The nucleotide composition of the mitochondrial DNA control region of 255 individuals was analyzed, and 31 haplotypes were found, with an estimated diversity Hd = 0.627, and a nucleotide diversity π = 0.00167. An analysis of molecular variance (AMOVA) revealed a fixation index Φ ST = -0.01118, representing an absence of population structure among the sampled regions of the Atlantic Ocean, and between the Atlantic and Indian Oceans. These results show a high degree of gene flow between the studied areas, with a single genetic stock and reduced population variability. In panmictic populations, conservation efforts can be concentrated in more restricted areas, being these representative of the total biodiversity of the species. When necessary, this strategy could be applied to the genetic maintenance of P. kamoharai.

Structure and Dynamics of the Shark Assemblage off Recife, Northeastern Brazil

Understanding the ecological factors that regulate elasmobranch abundance in nearshore waters is essential to effectively manage coastal ecosystems and promote conservation. However, little is known about elasmobranch populations in the western South Atlantic Ocean. An 8-year, standardized longline and drumline survey conducted in nearshore waters off Recife, northeastern Brazil, allowed us to describe the shark assemblage and to monitor abundance dynamics using zero-inflated generalized additive models. This region is mostly used by several carcharhinids and one ginglymostomid, but sphyrnids are also present. Blacknose sharks, Carcharhinus acronotus, were mostly mature individuals and declined in abundance throughout the survey, contrasting with nurse sharks, Ginglymostoma cirratum, which proliferated possibly due to this species being prohibited from all harvest since 2004 in this region. Tiger sharks, Galeocerdo cuvier, were mostly juveniles smaller than 200 cm and seem to use nearshore waters off Recife between January and September. No long-term trend in tiger shark abundance was discernible. Spatial distribution was similar in true coastal species (i.e. blacknose and nurse sharks) whereas tiger sharks were most abundant at the middle continental shelf. The sea surface temperature, tidal amplitude, wind direction, water turbidity, and pluviosity were all selected to predict shark abundance off Recife. Interspecific variability in abundance dynamics across spatiotemporal and environmental gradients suggest that the ecological processes regulating shark abundance are generally independent between species, which could add complexity to multi-species fisheries management frameworks. Yet, further research is warranted to ascertain trends at population levels in the South Atlantic Ocean.

Habitat use of the nurse shark, Ginglymostoma cirratum, off Recife, Northeast Brazil: a combined survey with longline and acoustic telemetry

The nurse shark, Ginglymostoma cirratum, is an abundant coastal species widely distributed on both sides of the tropical and subtropical Atlantic Ocean. Despite being an endangered species in Brazil, information on bio-ecological aspects of this species is still very scarce. This study investigates seasonal fluctuations in abundance, sex ratio and residency of nurse sharks in coastal waters off Recife, northeastern Brazil. Total length of the specimens caught ranged from 107 to 300 cm. Sex ratio for nurse sharks was 1.31♀:1♂ but it showed a strong variation throughout the year. About 8% of tagged sharks were recaptured after an average of 248 days at liberty, at distances between 0.04 and 6.23 km from the tagging site. A growth rate of 15.77 ± 2.53 cm/yr was obtained from total length data collected from three recaptured specimens. Nurse sharks demonstrated some signs of affinity for temperatures between 25º and 30°C and salinities between 34 and 37. The combined analysis of longline and telemetry data indicated possible differences in habitat usage between sexes of nurse sharks off Recife.

Stomach contents of the pelagic stingray (Pteroplatytrygon violacea) (elasmobranchii: dasyatidae) from the tropical atlantic

Universidade Federal Rural de Pernambuco - LEMAR/DEPAq (Av. Dom Manuel de Medeiros s/n, Dois Irmaos, 52171-900 Recife, PE, Brasil) E-mail: p.travassos@depaq.ufrpe.br; mari.trrr@gmail.com The pelagic stingray Pteroplatytrygon violacea (Bonaparte, 1832) is the only pelagic dasyatid ray occurring in tropical and subtropical waters of the Atlantic, Indian and Pacific Oceans (BIGELOW; SCHROEDER, 1953; MOLLET, 2002; ELLIS, 2007). This poorly known species was originally described from the Mediterranean Sea, and was first reported from the Atlantic by Bigelow & Schroeder (1962). The species has no commercial value, but is fairly abundant off the Southeastern United States representing about 2.5% in number of the catches by pelagic longlines between 1992-2000 (BEERKIRSHER et al., 2004). The first record in southern Brazilian waters was reported by Sadowski; Amorim (1977) and Mazzoleni; Schwingel (2002) subsequently recorded the pelagic stingray as a bycatch species regularly caught by tuna longliners off southern Brazil. Menni et al. (1995) reported on the presence of the pelagic stingray in northeastern Brazilian waters. Although the pelagic stingray is caught regularly by tuna longliners operating along the Brazilian coast, few biological data are available on the species. In this context, the stomach contents of the pelagic stingray were analyzed to provide more specific information on its feeding habits in the southwestern equatorial Atlantic Ocean. The sampled area was located between 40o- 25oW and 5oN-20oS (Fig. 1). All specimens were caught by the Research Vessel Riobaldo (CEPENE-IBAMA), in the years 1993, 1994 and 1995 through the Ecotuna Project, and by the Brazilian tuna longline fleet, in the years 2005 and 2006 (SEAP, Onboard Observer Program), in waters of 2000 to 5000 m local depth, with hook depth between 50 and 250 m along the longline. The specimens were stored on ice onboard, and at the laboratory, they were sexed and had their disc width measured to the nearest centimeter.

Spatio-temporal distribution and target species in a longline fishery off the southeastern coast of Brazil

In the present study, a cluster analysis, in relation to the species composition of the catches, was used to classify 6,486 fishing sets by a longline fleet based in Sao Paulo State, Brazil, from 1998 to 2006. Based on the proportions of 12 species and three broader species groups, three clusters were identified: C1: other fishes; C2: blue shark; C3: swordfish. Results indicated that the fleet targeted mainly blue shark and swordfish and also showed that the blue shark importance in this fishery has been growing progressively trough the years. Offshore areas were exploited mainly in the first and fourth quarters (from 2001 mainly), while the fishing effort was more concentrated near the continental shelf break, during the second and third quarters (for the whole period). The longline fishery based in Sao Paulo State changed fishing strategy to target different species which produced important changes in catch-per-unit-effort (CPUE) of the main species caught. Cluster analysis seems to have appropriately identified these changes over time, which is an important information, often missing in logbooks.