Population size and survivorship for juvenile lemon sharks (Negaprion brevirostris) on their nursery grounds at a marine protected area in Brazil

Abstract

Sharks face a number of obstacles for surviving their first several years of life and many species occupy nursery areas. Although estimates of survival, particularly for young age classes, are essential for assessing, monitoring and effectively managing animal populations, there have been relatively few calculations of survival within shark populations and even fewer estimates based on direct methods for sharks on their nursery grounds. We used tag-recapture methods to estimate the population size and survival of juvenile lemon sharks (Negaprion brevirostris) on their nursery grounds at Atol das Rocas, a marine protected area in Brazil. Sharks were sampled from1999 to 2003. Population size estimates ranged from 12 to 100 juvenile sharks and survival estimates ranged between 24-54% with a mean of 44.6% over the most robust sampling periods. The population of juvenile lemon sharks declined over the course of our study, whereas survival rates may have increased over the same time period. Even a modest level of fishing and removal of mature females in adjacent areas may dramatically affect small populations of sharks within a small and isolated nursery such as Atol das Rocas. The lower survival rates and population size at Atol das Rocas could be the result of differences in physical characteristics of this nursery in comparison to others used by lemon sharks in the northwestern Atlantic. Such comparatively lower populational parameters suggest that the population of young lemon sharks is fragile at the Atol das Rocas nursery.<br>Os tubarões enfrentam muitos obstáculos para sobreviver nos primeiros anos de vida e muitas espécies ocupam áreas de berçário. Embora estimativas de sobrevivência, particularmente para jovens, sejam essenciais para acessar, monitorar e manejar efetivamente populações animais, existem poucos cálculos destas estimativas para populações de tubarões e poucas estimativas baseadas em métodos diretos para estes animais em suas áreas de berçário. Métodos de marcação e recaptura foram utilizados no presente estudo para estimar o tamanho populacional e a sobrevivência de jovens tubarões-limão (Negaprion brevirostris) em uma área de berçário na Reserva Biológica do Atol das Rocas, Brasil. Os indivíduos foram amostrados entre 1999 e 2003 e as estimativas de tamanho populacional variaram entre 12 a 100 indivíduos jovens e a taxa de sobrevivência entre 24 e 54%, com média de 44,6% durante o período de amostragem mais robusto. A população destes tubarões jovens diminuiu ao longo de nosso estudo, ainda que as taxas de sobrevivência tenham aumentado durante o mesmo período. Mesmo um nível moderado de pesca e a remoção de fêmeas maduras em áreas adjacentes podem afetar dramaticamente pequenas populações de tubarões num berçário pequeno e isolado como o Atol das Rocas. As taxas de sobrevivência e tamanho populacional relativamente mais baixos em Rocas podem ser resultado das diferenças nas características físicas deste berçário, comparadas a outros utilizados pela espécie no Atlântico norte-ocidental. Tais par...

Spatial patterns of fish standing biomass across Brazilian reefs

“…In contrast, sharks are very common in the inhabited, but protected Fernando de Noronha Archipelago and in the remote, but also protected Atol das Rocas. These islands are nursery grounds for three shark species, the Caribbean reef shark Carcharhinus perezii (Poey 1876), the lemon shark Negaprion brevirostris (Poey 1868) and the nurse shark Ginglymostoma cirratum (Bonnaterre 1788) (Castro & Rosa, ; Freitas et al ., , , Garla et al ., , ). Along the coast, only G. cirratum were observed in two tropical sites and at most surveyed sites sharks were never recorded.…”

Mortality rates for two shark species occupying a shared coastal environment

“…Mortality rates for juvenile C. amboinensis estimated directly from telemetry data in this study were substantially lower than those reported for juveniles of other species using coastal marine environments. For example, direct estimates of mortality ranged from 0.35-0.75 y −1 for juvenile lemon sharks (Negaprion brevirostris) (Manire and Gruber, 1993;Gruber et al, 2001;de Freitas et al, 2009) and 0.61-0.91 y −1 for juvenile C. limbatus (Heupel and Simpfendorfer, 2002). Rather, mortality rates for juvenile C. amboinensis (total = 0.11-0.13 y −1 ) were more similar to those reported for juvenile bull sharks (Carcharhinus leucas) (total = 0.00-0.36 y −1 ; Heupel and Simpfendorfer, 2011).…”

Green turtle (Chelonia mydas) nesting on Atol das Rocas, north-eastern Brazil, 1990–2008

“…The main sea bird species that nest regularly on the atoll are: masked booby ( Sula dactylatra ), brown booby ( Sula leucogaster ), brown noddy ( Anous stolidus ), black noddy ( Anous minutus ) and sooty tern ( Sterna fuscata ) (Schulz Neto, 1998). In the sea inside or around the atoll, dolphins, sharks, a diversity of other fishes and other marine fauna can be found (Floeter & Gasparini, 2000; Paiva et al , 2007; Baracho et al , 2008; Freitas et al , 2009). The Atol das Rocas Biological Reserve, including an ocean area of about 360 km 2 around the atoll (up to the 1000 m isobath), was established on 5 June 1979 by the Brazilian federal government (Decree No.…”