InteractIons of PatagonIan toothfIsh fIsherIes wIth kIller and sPerm whales In the crozet Islands exclusIve economIc zone: an assessment of dePredatIon levels and InsIghts on PossIble mItIgatIon strategIes

Abstract

Within the Crozet Islands Exclusive Economic Zone (EEZ), the Patagonian toothfish (Dissostichus eleginoides) longline fishery is exposed to high levels of depredation by killer (Orcinus orca) and sperm whales (Physeter macrocephalus). From 2003 to 2008, sperm whales alone, killer whales alone, and the two species co-occurring were observed on 32.6%, 18.6% and 23.4% respectively of the 4 289 hauled lines. It was estimated that a total of 571 tonnes (€4.8 million) of Patagonian toothfish were lost due to depredation by killer whales and both killer and sperm whales. Killer whales were found to be responsible for the largest part of this loss (>75%), while sperm whales had a lower impact (>25%). Photo-identification data revealed 35 killer whales belonging to four different pods were involved in 81.3% of the interactions. Significant variations of interaction rates with killer whales were detected between vessels suggesting the influence of operational factors on depredation. When killer whales were absent at the beginning of the line hauling process, short lines ( 40 n miles to prevent killer whales from finding them within a few hours. Although more data are still needed to better understand the way killer whales search and detect vessels, this study gives preliminary insights into possible mitigation solutions to the widespread depredation issue.