SynopsisWe assessed information on the population structure of the nurse shark, Ginglymostoma cirratum, at Atol das Rocas, northeastern Brazil, through underwater observations. Based on photographic records of natural distinctive marks for individual recognition, we used probabilistic estimators (Petersen-Bailey and Jolly-Seber) to assess population size. We found that 46% of the sharks (194 individuals) had distinctive marks.

Movement patterns and habitat use of juvenile lemon sharks Negaprion brevirostris were monitored at Atol das Rocas, Brazil, an atypical nursery area for this species, characterized by extreme tides and a lack of seagrass flats and mangroves. Twenty-three sharks carrying transmitters were monitored using an array of bottom-fixed automated receivers during 3 trips over a total of 60 d. Transmitters were recorded on receivers over 13 000 times, and the majority of sharks were detected more than 100 times. Newborn sharks (60 to 80 cm total length, TL) showed restricted but repeated movements between small tide pools on reef flats at low tide and a small, shallow, nearby tidal creek at high tide. Larger sharks (up to 106 cm TL) sampled 6 and 20 mo after the study in March 2000 frequented the tidal creek and several other locations at high tide and a variety of larger pools at low tide, and in general exhibited more extensive movements within the atoll than did newborn sharks. Sharks approaching 2 yr of age were generally observed in specific pools or shallow water locations within the atoll during high and low tides, but also expanded their movements to include more of the atoll. Throughout the study, young lemon sharks appeared to concentrate movements within shallow-water low-tide refuges and separate high tidal areas. Movement patterns of sharks in Atol das Rocas differ from those at other well-studied lemon shark nursery locations, where individuals continuously occupy shallow flats and mangrove habitats. Nevertheless, lemon sharks in general restrict their movements to shallow-water habitats regardless of the specific nursery area occupied. This behavior is most likely related to predator avoidance. This study provides an example of the interaction between the physical environment and the biology of animals -in this case, the influence of the physical characteristics of a nursery area and the behavioral ecology of young lemon sharks. KEY WORDS: Shark nurseries · Tidal fluctuation · Refuging · Movement patterns · Predator avoidanceResale or republication not permitted without written consent of the publisher

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Lemon sharks Negaprion brevirostris were sampled in the Atol das Rocas, a nursery area, on nine occasions from March 1999 to October 2003, during which 157 individuals were tagged and 35 were recaptured. The male : female sex ratio of captured individuals was 1 : 1Á12. Mean AE S.D. growth rates were 24Á7 AE 3Á4 cm year À1 in total length (L T ), 20Á7 AE 3Á2 cm year À1 in fork length, and 19Á5 AE 2Á7 cm year À1 in precaudal length. There was no significant difference in growth rates between males and females. Mean AE S.D. increase in mass was 2565 AE 762 g year À1 . The von Bertalanffy growth parameters estimated by the Fabens method based on L T were: k ¼ 0Á077, L 1 ¼ 399Á9 cm and t 0 ¼ À2Á16. Despite the large variation of environmental conditions, particularly of tidal range and currents, and the lack of protective mangrove cover in the nursery area at Atol das Rocas, juvenile lemon sharks grew relatively faster than at other nurseries. Such rapid growth could be a response to abundant food availability or high risk of predation by adults that enter the nursery area.

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The diversity of the marine Brazilian Chondrichthyes is focused in historical terms since the beginning of the 20 th century, by the analysis of the main publications produced in Brazil and other American countries with respect to the number of species of sharks, rays and chimaeras occurring in this country. In this context, the first volume of the "Manual de Peixes Marinhos do Sudeste do Brasil", published in 1977 by José Lima de Figueiredo, stands out as a landmark in the knowledge about Brazilian Chondrichthyes. This work included 72 chondrichthyan species, and despite its regional restriction to southeastern Brazil, this figure represented a 34% increment in the number of species previously recorded in faunal studies on the Brazilian coast. Containing identification keys, diagnoses and illustrations, the first volume of the "Manual de Peixes Marinhos do Sudeste" became the main reference for the identification of marine chondrichthyans in Brazil. The present paper presents an overview of the conservation status of the group in Brazil, and as an original contribution, an updated record of the diversity of Brazilian marine Chondrichthyes, totaling 12 orders, 36 families, 79 genera and 165 species.

The present work aims to determine and analyse the distribution of individuals of different size-classes of the southern stingray, Dasyatis americana, in distinct habitats at Fernando de Noronha Archipelago. The stingrays were visually sampled, quantified and described according to a standard protocol through intensive search method during direct observations. The relationships among individuals of various disc length (DL) classes and their habitat features were described by the correspondence analysis. A total of 356 individuals were sampled. Individuals between 15 and 35 cm DL were observed mostly at the beaches while the greater DLs were strongly related to reef environments. This distribution reflects a tendency of the younger stingrays to occupy the shallow beach areas, while larger individuals move to deeper waters with reef characteristics during the ontogeny.

Habitat use and the processes which determine fish distribution were evaluated at the reef flat and reef crest zones of a tropical, algal-dominated reef. Our comparisons indicated significant differences in the majority of the evaluated environmental characteristics between zones. Also, significant differences in the abundances of twelve, from thirteen analyzed species, were observed within and betweensites. According to null models, non-random patterns of species co-occurrences were significant, suggesting that fish guilds in both zones were non-randomly structured. Unexpectedly, structural complexity negatively affected overall species richness, but had a major positive influence on highly site-attached species such as a damselfish. Depth and substrate composition, particularly macroalgae cover, were positive determinants for the fish assemblage structure in the studied reef, prevailing over factors such as structural complexity and live coral cover. Our results are conflicting with other studies carried out in coraldominated reefs of the Caribbean and Pacific, therefore supporting the idea that the factors which may potentially influence reef fish composition are highly site-dependent and variable.