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

Abstract

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 Smith 1828), 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 (c. 250–150 mya). 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 fertilization 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). In some respects, the behavioural, ecological and life-history strategies of elasmobranchs share certain characteristics that are arguably more similar to mammals and birds than other fishes. These include, for example, sex-biased dispersal (Pardini et al., 2001) and long-distance return migrations from foraging habitat to breeding grounds (Lea et al., 2015a). These attributes, in addition to other more unique features, have also made elasmobranchs important model organisms for developmental, biomedical and evolutionary research (Oulion et al., 2011). Furthermore, elasmobranchs occupy a very broad range of habitats worldwide and have a key role in the functioning of ecosystems (Heithaus et al., 2008). Taken together, this identifies elasmobranchs as an important group to study for advancing fundamental biological knowledge in key fields ranging from molecular genetics and genomics to physiology, and from behaviour to population and community ecology. Life-history traits such as slow growth, late maturity and low fecundity, however, make elasmobranchs less resilient to exploitation (Dulvy et al., 2014). Many sharks, skates and rays are highly valued worldwide by commercial fisheries, exploitation that has led to dramatic declines in the population levels of numerous species (Baum et al., 2003; Ferretti et al., 2010). There is particular concern that target and by-catch fisheries are depleting populations below sustainable levels where recovery may not be possible, or at best may be very slow, even if fishing pressure is removed (Field et al., 2009). An increasing number of elasmobranchs are being listed in the IUCN Red List of threatened species, with some larger species of greater economic value now being listed on the Convention of International Trade in Endangered Species (CITES) (Dulvy et al., 2014). The conservation of elasmobranch populations in the face of pressures such as the expansion of industrialized fisheries, the degradation or removal of habitats and, for many species, little or no management requires novel solutions for sustainable exploitation. These concerns about elasmobranch populations and the need for science to inform conservation measures provided the backdrop to the Fisheries Society of the British Isles (FSBI) Annual Symposium on the ‘Biology, ecology and conservation of elasmobranchs: recent advances and new frontiers’, that took place in Plymouth, U.K., from 27 to 31 July 2015. The key aim was to explore how new scientific and technological approaches, such as biotelemetry, robotics, reproductive physiology and genomics, can contribute to improved conservation. This special issue of the Journal of Fish Biology arises from this symposium. The city of Plymouth in the south-west of England in the U.K. was an inspired choice of location for this FSBI symposium because it has a long h