Toothed whale and shark depredation indicators: A case study from the Reunion Island and Seychelles pelagic longline fisheries.
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. Theref...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Public Library of Science (PLoS)
2018-01-01
|
| Series: | PLoS ONE |
| Online Access: | http://europepmc.org/articles/PMC6086455?pdf=render |
| _version_ | 1819126044720889856 |
|---|---|
| author | Njaratiana Rabearisoa Philippe S Sabarros Evgeny V Romanov Vincent Lucas Pascal Bach |
| author_facet | Njaratiana Rabearisoa Philippe S Sabarros Evgeny V Romanov Vincent Lucas Pascal Bach |
| author_sort | Njaratiana Rabearisoa |
| collection | DOAJ |
| description | 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 worldwide. |
| first_indexed | 2024-12-22T07:49:47Z |
| format | Article |
| id | doaj.art-e61ce0e2d8874157bf19009787bdc020 |
| institution | Directory Open Access Journal |
| issn | 1932-6203 |
| language | English |
| last_indexed | 2024-12-22T07:49:47Z |
| publishDate | 2018-01-01 |
| publisher | Public Library of Science (PLoS) |
| record_format | Article |
| series | PLoS ONE |
| spelling | doaj.art-e61ce0e2d8874157bf19009787bdc0202022-12-21T18:33:32ZengPublic Library of Science (PLoS)PLoS ONE1932-62032018-01-01138e020203710.1371/journal.pone.0202037Toothed whale and shark depredation indicators: A case study from the Reunion Island and Seychelles pelagic longline fisheries.Njaratiana RabearisoaPhilippe S SabarrosEvgeny V RomanovVincent LucasPascal BachDepredation 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 worldwide.http://europepmc.org/articles/PMC6086455?pdf=render |
| spellingShingle | Njaratiana Rabearisoa Philippe S Sabarros Evgeny V Romanov Vincent Lucas Pascal Bach Toothed whale and shark depredation indicators: A case study from the Reunion Island and Seychelles pelagic longline fisheries. PLoS ONE |
| title | Toothed whale and shark depredation indicators: A case study from the Reunion Island and Seychelles pelagic longline fisheries. |
| title_full | Toothed whale and shark depredation indicators: A case study from the Reunion Island and Seychelles pelagic longline fisheries. |
| title_fullStr | Toothed whale and shark depredation indicators: A case study from the Reunion Island and Seychelles pelagic longline fisheries. |
| title_full_unstemmed | Toothed whale and shark depredation indicators: A case study from the Reunion Island and Seychelles pelagic longline fisheries. |
| title_short | Toothed whale and shark depredation indicators: A case study from the Reunion Island and Seychelles pelagic longline fisheries. |
| title_sort | toothed whale and shark depredation indicators a case study from the reunion island and seychelles pelagic longline fisheries |
| url | http://europepmc.org/articles/PMC6086455?pdf=render |
| work_keys_str_mv | AT njaratianarabearisoa toothedwhaleandsharkdepredationindicatorsacasestudyfromthereunionislandandseychellespelagiclonglinefisheries AT philippessabarros toothedwhaleandsharkdepredationindicatorsacasestudyfromthereunionislandandseychellespelagiclonglinefisheries AT evgenyvromanov toothedwhaleandsharkdepredationindicatorsacasestudyfromthereunionislandandseychellespelagiclonglinefisheries AT vincentlucas toothedwhaleandsharkdepredationindicatorsacasestudyfromthereunionislandandseychellespelagiclonglinefisheries AT pascalbach toothedwhaleandsharkdepredationindicatorsacasestudyfromthereunionislandandseychellespelagiclonglinefisheries |