The biology, ecology and conservation of elasmobranchs: recent advances and new frontiers.

The elasmobranchs (sharks, skates and rays) are cartilaginous fishes that are important predatory and scavenging species within aquatic ecosystems, and as living resources to human societies globally in cultural, economic, health, biodiversity and conservation contexts. There are over 900 extant species, including the world’s largest fish (the whale shark Rhincodon typus), that arose sometime during c. 400 million years of independent evolution, with the main living families having first appeared sometime between the Permian and Jurassic Periods (~250–150 million years ago). Extant elasmobranchs possess an intriguing set of biological characteristics, including, for example, larger brains than other ectothermic vertebrates (Northcutt, 1977), slow growth and late age at maturity (Cailliet & Goldman, 2004), internal fertilisation and female sperm storage (Metten, 1939; Feldheim et al., 2002), diverse reproductive modes including oviparity and viviparity (Dulvy & Reynolds, 1997), relatively low fecundity, and social systems with dominance hierarchies and segregation by sex and age (Wearmouth & Sims 2008; Mucientes et al., 2009).