Sharks by-catch observed on bottom longlines fishery off the Kerguelen Islands in 2006–2016, with a focus on Etmopterus viator

Data collected by fishery observers aboard French deep-sea bottom longline vessels, targeting Patagonian toothfish (Dissostichus eleginoides), were examined to quantify and describe shark bycatch within the Kerguelen EEZ (northern part of the plateau). From 2006 to 2016, crew reported the total catches of the line and observers were asked to identify and count fish bycatch on 25% of the total fishing effort. A total of 26 203 longline hauls and more than 55 million hooks were checked by observers reporting 29 500 sharks. Four shark species were identified (Etmopterus viator, Somniosus antarcticus, Centroscymnus coelolepis and Lamna nasus) among which E. viator was numerically largely dominant (99%). An abundance index (number of shark per 1 000 hooks observed) was used to show bathymetric and geographical distributions and biological data were also analysed. There were marked differences between distributions of the shark bycatch species and their relative abundance. Length-frequency for E. viator showed a bimodal distribution characterizing a long-lived species and stopping growth of adults. The study also revealed females significantly taller than males and the deepest record of E. viator in Kerguelen waters and probably for the species.