[MARMAM] New publication: Toothed whale and shark depredation indicators in the southwest Indian Ocean

Njaratiana Rabearisoa njaratiana.rabearisoa at ird.fr
Tue Aug 14 06:10:09 PDT 2018

Dear all,

We are pleased to announce the publication of the following article:
Rabearisoa, N., Sabarros, P.S., Romanov, E.V., Lucas, V., Bach, P., 
2018. Toothed whale and shark depredation indicators: A case study from 
the Reunion Island and Seychelles pelagic longline fisheries. PLOS ONE 
13, e0202037. https://doi.org/10.1371/journal.pone.0202037

Depredation in marine ecosystems is defined as the damage or removal of 
fish or bait from fishing gear by predators. Depredation raises concerns 
about the conservation of species involved, fisheries yield and 
profitability, and reference points based on stock assessment of 
depredated species. Therefore, the development of accurate indicators to 
assess the impact of depredation is needed. Both the Reunion Island and 
the Seychelles archipelago pelagic longline fisheries targeting 
swordfish (Xiphias gladius) and tuna (Thunnus spp.) are affected by 
depredation from toothed whales and pelagic sharks. In this study, we 
used fishery data collected between 2004 and 2015 to propose depredation 
indicators and to assess depredation levels in both fisheries. For both 
fisheries, the interaction rate (depredation occurrence) was 
significantly higher for shark compared to toothed whale depredation. 
However, when depredation occurred, toothed whale depredation impact was 
significantly higher than shark depredation impact, with higher 
depredation per unit effort (number of fish depredated per 1000 hooks) 
and damage rate (proportion of fish depredated per depredated set). The 
gross depredation rate in the Seychelles was 18.3%. A slight increase of 
the gross depredation rate was observed for the Reunion Island longline 
fleet from 2011 (4.1% in 2007–2010 and 4.4% in 2011–2015). Economic 
losses due to depredation were estimated by using these indicators and 
published official statistics. A loss of 0.09 EUR/hook due to 
depredation was estimated for the Reunion Island longline fleet, and 
0.86 EUR/hook for the Seychelles. These results suggest a southward 
decreasing toothed whale and shark depredation gradient in the southwest 
Indian Ocean. Seychelles depredation levels are among the highest 
observed in the world revealing this area as a “hotspot” of interaction 
between pelagic longline fisheries and toothed whales. This study also 
highlights the need for a set of depredation indicators to allow for a 
global comparison of depredation rates among various fishing grounds 

This is an open access publicationavailable from: 

Any request can be made to njaratiana.rabearisoa at ird.fr




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