Search

Context: The blackspot shark (Carcharhinus sealei) is a small-bodied coastal shark often incidentally caught in fisheries across South-east Asia. Aims: This study aimed to document the species' biology, ecology, fisheries and markets to inform conservation. Methods: In total, 103 blackspot sharks from Indonesia (n = 101) and Singapore (n = 2) were examined to determine biological parameters (growth rate, age at maturity, reproductive traits and diet). An interview with a Singaporean seafood supplier gave insight to population trends, fisheries and markets. Key results: Males attained a maximum age of 9 years, the smallest mature individual measured 709-mm stretched total length (STL), with 50% reaching maturity at 6.15 years. Females attained a maximum age of 11 years, the smallest mature individual measured 730 mm STL, with 50% reaching maturity at 6.12 years. The species has an overall growth rate (k) of 0.37 year−1. Reproduction was asynchronous, with only two pups produced per litter. Crustaceans dominated the diet of juveniles, whereas bony fishes and cephalopods dominated the diets of adult males and adult females respectively. Conclusions: Blackspot sharks have a moderately fast growth rate, but a late age-at-maturity and a low fecundity. Diet differed between the sexes as well as adults and juveniles. Implications: The low fecundity and late maturity of blackspot sharks increase their vulnerability to exploitation. Blackspot sharks are now listed on CITES-Appendix II, but mortality may remain high because they are reportedly often caught incidentally. Blackspot sharks from Riau Islands, Indonesia, have a late maturity (~6 years old) and low fecundity (litters of two pups). Mature males primarily eat bony fishes, mature females primarily eat cephalopods, whereas juveniles primarily eat crustaceans. A seafood supplier who was interviewed has perceived population declines and stated that the species is mostly caught incidentally. [ABSTRACT FROM AUTHOR]

The age and growth of subtropical populations of the Brazilian and Caribbean sharpnose sharks (Rhizoprionodon lalandii and R. porosus respectively) were determined by combining direct and indirect ageing methods, maximising the use of available information. Using vertebrae ageing for R. lalandii , the theoretical maximum length L ∞ and growth coefficient k were 661.9 mm and 1.14 year–1 for males and 751.7 mm and 0.59 year–1 for females. Vertebrae were not sampled for R. porosus. Values of L ∞ and k from electronic length–frequency analyses (ELEFAN) were 762 mm and 0.71 year–1 for male R. lalandii , 791 mm and 0.67 year–1 for female R. lalandii , 1040 mm and 0.41 year–1 for male R. porosus and 1165 mm and 0.31 year–1 for female R. porosus. Growth during the first year of life in relation to birth size was 80.3% for R. lalandii and 55% for R. porosus. Both species exhibit rapid growth, primarily in the first year of life. The growth estimates for R. lalandii and R. porosus are even faster than those reported in previous studies from tropical populations. This study estimated the age and growth parameters of two small coastal shark species for the first time in subtropical waters; unlike most sharks, both species exhibited very fast growth. Considering that these species are the most captured sharks in the study area, the results are crucial for fishery management and for the evaluation of the vulnerability status of the two species. [ABSTRACT FROM AUTHOR]

A drone was used to study the richness and behaviour of scavengers attracted to the carcass of a sperm whale (Physeter microcephalus) in Seychelles, Western Indian Ocean. Over 30 sharks of 3 species (tiger shark Galeocerdo cuvier , bull shark Carcharhinus leucas and tawny nurse shark Nebrius ferrugineus) were recorded scavenging on the carcass. Tiger sharks dominated the scavenging, but with no evidence of agonistic behaviours or hierarchy, and may have facilitated scavenging by other species. Drone use allowed the analysis of such behaviours without observer influence, providing new insights into communal scavenging events. For the first time, multiple tiger, bull and nurse sharks were all recorded feeding on the same sperm whale carcass. Moreover, the event was observed using a drone, meaning that the sharks were undisturbed by humans and exhibited natural behaviour. Contrary to expectation, there was no aggression between any of the sharks. Instead, they all fed calmly alongside each other during this communal scavenging event. [ABSTRACT FROM AUTHOR]

We report the first documented case of bicephaly in a chondrichthyan, the southern fiddler ray, Trygonorrhina dumerilii, in Australian waters. Females in the latter stages of pregnancy, as confirmed by ultrasound, were captured by hand in Swan Bay, Victoria (38.252°S, 144.616°E) in February 2013 and transported to aquaria. Up to 10 females gave birth in aquaria in early April 2013 to 11 neonates, one of which was a still-born, bicephalic neonate. Magnetic resonance imagery of the bicephalic neonate displayed the presence of two parallel vertebral columns running the entire length of the animal, diverging into two well formed heads. Morphological measurements were also made, comparing the bicephalic neonate to normal neonates. The cause of bicephaly is unknown, although congenital and environmental stressors during development may cause this condition. We present the first documented species of shark or ray in Australia to give birth to a two-headed offspring. Using magnetic resonance imagery (MRI), we found two parallel vertebral columns running the entire length of the offspring, diverging into two well formed heads. The cause of such births defects is unknown, although they may be linked to congenital and environmental stressors during embryonic development. [ABSTRACT FROM AUTHOR]