IMIS

Recent anthropogenic pressures including overfishing, climate change and habitat destruction have directly caused the global extinction of several marine species including chondrichthyans (sharks, skates, rays and chimeras). Overall chondrichthyan extinction risk is substantially higher than for most other vertebrates, due to their typical ëK strategistí life history characteristics; slow growth, late age of sexual maturity, low fecundity, long life spans and well-developed offspring making them vulnerable to over exploitation and average global exploitation rates often exceed the rebound rates for many species. In many ecosystems elasmobranchs (sharks, skates and rays) fulfil the role of top level predators, the loss of predators often risks wider ecosystem degradation and can act as a herald for marked changes within ecosystems. Therefore, improved management of elasmobranch populations is needed urgently to ensure the future stability and recovery of marine ecosystems with functional top predators. Despite the wide-ranging behaviour of some elasmobranchs, it has been shown that many species make use of the same areas repeatedly either in the form of site fidelity or residency. The incorporation of such behaviours into the management plans for mobile species may allow for strategies such as Marine Protected Areas to be used. There is evidence that spurdog (Squalus acanthias) displays seasonal residency within a Scottish loch, Loch Etive, a sea loch on the west coast of Scotland, however, the extent to which this occurs between age and sex classes occurs. This was investigated using a static acoustic array and internally implanted acoustic tags on a range of age and sex classes.