Deepwater Chondrichthyans: Biodiversity, Life History & Fisheries

Despite the widespread recognition of the vulnerability of deepwater chondrichthyan fishes (sharks, batoids and holocephalans) to overfishing and their potential inability to recover from depletion, there is a lack of a concise overview of the present status of knowledge concerning the biodiversity and life history of this group. This report provides a global review of this data, together with fisheries information in order to provide a sound summary to inform future research, conservation and management directions.

For the purposes of this project, deepwater chondrichthyans have been defined as those sharks, rays and holocephalans whose distribution is predominantly at, are restricted to, or spend the majority of their lifecycle at, depths below 200m. This depth is generally recognised as the continental and insular shelf edge, and therefore, deepwater species are those occurring on or over the continental and insular slopes and beyond, including the abyssal plains and oceanic seamounts.

Of the global chondrichthyan fauna (1193 species), 581 species are considered to be deepwater (48.7% of the global total). The deepwater fauna is divided between 278 sharks (55.8% of global), 257 batoids (39.8% of global) and 46 holocephalans (93.9% of global). The bulk of the deepwater shark fauna is attributable to the squaloid dogfishes (Order Squaliformes) and scyliorhinid catsharks (Order Carcharhiniformes, Family Scyliorhinidae), together comprising 84.5% of deepsea sharks. Three families of skates (Arhynchobatidae, Rajidae and Anacanthobatidae) dominate the deepwater batoid fauna, together comprising 89.9% of deepsea batoids. A full annotated checklist of deepwater chondrichthyans is incorporated into the report.