Bioecology and movements of bull sharks, Carcharhinus leucas , caught in a long-term longline survey off northeastern Brazil

Abstract

Bioecology and movements of bull sharks, Carcharhinus leucas, caught in a long-term longline survey off northeastern BrazilYuri V. Niella 1, 2 , André S. Afonso 2 and Fábio H. V. Hazin 2 A robust understanding of habitat usage by coastal shark species, and how it overlaps with human presence in denselypopulated regions is needed to inform the development of efficient conservation strategies for these important top predators. An intensive longline survey conducted in nearshore waters off northeastern Brazil from 2004 through 2014 caught a total of 18 bull sharks (Carcharhinus leucas) (male-female ratio = 0.63:1), which can be dangerous to humans. Although most sharks were sexually mature, there was no evidence that this region could be used as a parturition or nursery area. Prey items identified in the guts of the sharks comprised teleosts, mollusks and elasmobranchs. Additionally, one satellite-tagged bull shark covered a great distance (> 3,000 km) in 75 days at liberty, making most use of shallow waters (< 20 m depth) and presumably also entering an estuarine area. Although bull sharks are not an important fishery resource in this region, such a reduced abundance coupled with its affinity for coastal and inshore habitats highlights the potential vulnerability of C. leucas to deleterious anthropic interferences off northeastern Brazil.Keywords: Drumline, Longline, Maturity status, Pop-up satellite archival tag, Recife.Um melhor entendimento sobre a utilização de hábitat das espécies de tubarões costeiros, e como ela se sobrepõe à presença humana em regiões altamente populosas, se faz necessário a fim de subsidiar o desenvolvimento de eficientes medidas de conservação para esses importantes predadores de topo. Um estudo intensivo utilizando espinhel, conduzido em águas costeiras do nordeste do Brasil entre os anos de 2004 e 2014, capturou um total de 18 tubarões cabeça-chata (Carcharhinus leucas) (proporção macho-fêmea = 0,63:1), os quais podem ser perigosos para humanos. Apesar da maioria dos tubarões estarem sexualmente maduros, não houve evidências de que essa região esteja sendo utilizada como uma área de parto ou berçário. Entre os itens alimentares identificados foram encontrados teleósteos, moluscos e elasmobrânquios. Além disso, um tubarão cabeça-chata marcado com um transmissor satélite percorreu uma grande distância (> 3.000 km) em 75 dias em liberdade, fazendo o uso de águas superficiais (< 20 m profundidade) e presumivelmente entrando em uma área estuarina. Apesar de os tubarões cabeça-chata não corresponderem a um recurso pesqueiro importante nessa região, tal reduzida abundância juntamente com a sua afinidade por hábitats costeiros reforçam a potencial vulnerabilidade de C. leucas às interferências antrópicas deletérias ao longo da costa nordeste do Brasil.

Residency of bull sharks, Carcharhinus leucas (Carcharhiniformes: Carcharhinidae), at San Pedrillo Islet in Islas Murciélago, North Pacific of Costa Rica

“…Between June 2013 and September 2014, we tagged ten adult female bull sharks (C. leucas) at San Pedrillo, Islas Murciélago. Based on the approximate size of the individuals (> 2 m total length) we classified them as "adults" following the maturity size estimation determined in the Gulf of México and Northern Brazil (Cruz-Martínez, Chiappa-Carrara, & Arenas-Fuentes, 2004;Niella, Afonso, & Hazin, 2017). During the study period (June 2013 to February 2015) a total of 59,798 detections were recorded by the acoustic receiver.…”

“…Several studies have reported local migrations of bull sharks, which is correlated to seasonal changes (Daly et al, 2014;Niella, Afonso, & Hazin, 2017). Satellite tags on bull sharks have revealed important coastal migrations, thus contradicting many theories that this species is sedentary in coastal waters, such is the case in the Gulf of Mexico, where tagged bull sharks covered between 2 to 1 500 km in only 85 days, using primarily temperate shallow waters (> 20 m depth) (Carlson et al, 2010).…”

Short Communication: The presence of Bull shark Carcharhinus leucas (Elasmobranchii: Carcharhinidae) in the fresh waters of Sumatra, Indonesia

“…Estuarine sharks such as C. leucas are potentially highly vulnerable to urban habitat modification, as they are subject to not just the same biological constraints as their oceanic counterparts but also additional habitat constraints not faced by their stenohaline relatives (Werry et al 2012;Niella et al 2017). Estuarine and river habitats have more limited volume and their physicochemical properties vary widely (Potter et al 2015;Ceccarelli et al 2013).…”

Aggregative capacity of experimental anchored Fish Aggregating Devices (aFADs) in Northeastern Brazil revealed through electronic tagging data

“…Telemetry studies with pelagic fish other than elasmobranchs in Brazil have only been published for Thunnus albacares with three tagged individuals (Travassos et al, 2009), and for Istiophorus platypterus with four fish (Mourato et al, 2014), highlighting the importance of the present results. The acoustic telemetry articles published with sharks and rays (Bezerra et al, 2019;Branco-Nunes et al, 2016;Ferreira et al, 2013;Niella et al, 2017) also dealt with similar or lower number of tagged fish compared to this study.…”