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Assessing losses due to depredation

This study assesses losses due to depredation in fishing operations using a grid-based approach and comparing catch rates. The preliminary results show that losses in Crozet and Kerguelen are 30% and 5% respectively. Another method involving grenadier as a confirmatory measure is also presented. The study also explores the impact of different proportions of toothfish and grenadier on the overall losses.

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Assessing losses due to depredation

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  1. Assessing losses due to depredation N. Gasco, P. Tixier, C. Guinet

  2. Can we count what’s left on the line? This is the exception

  3. Depredation is highly variable in space So we use a grid to take this into account: 0,2° grid The common method consists in comparing catch rates First published in 2006 for Crozet and Kerguelen

  4. comparing catch rates ABSENCE 300 g/hook 100 g/hook Catch rate decrease: 200g/hook Losses: 200g/hook X 1 000 000 hooks (in presence) = 200 tons

  5. Assessing losses: comparing catch rates For each case: For each cell: and and + Total amount of fish lost

  6. Preliminary results: Overall: CROZET 30% and KERGUELEN 5% N. Gasco, P. Tixier, G. Duhamel, C. Guinet, CCAMLR Science, In press

  7. Second method to confirm results through grenadier • A wide spread bycatch • They don’t seem to be affected by depredation N. Gasco, P. Tixier, G. Duhamel, C. Guinet, CCAMLR Science, In press

  8. Second method to confirm results through grenadier If the proportion between toothfish and grenadier is half and half in absence of whales 50% 50% N. Gasco, P. Tixier, G. Duhamel, C. Guinet, CCAMLR Science, In press

  9. Second method to confirm results through grenadier 50% 50% If take half of the toothfish but no grenadier 67% x x x x x 33% N. Gasco, P. Tixier, G. Duhamel, C. Guinet, CCAMLR Science, In press

  10. Second method to confirm results through grenadier 67% 50% 50% How many toothfish are missing to go from: To: 33% x x x x x Assess the number of fish lost to N. Gasco, P. Tixier, G. Duhamel, C. Guinet, CCAMLR Science, In press

  11. Comparing methods We calculated the losses with the grenadier method using a 0.2° size grid Results we compared with the same cells with the CPUE method using number (instead of weight) N. Gasco, P. Tixier, G. Duhamel, C. Guinet, CCAMLR Science, In press

  12. Comparing methods CPUE Method Grenadier Method -The grenadier method supports the results obtained by the cpue method - it only works if there are enough grenadier N. Gasco, P. Tixier, G. Duhamel, C. Guinet, CCAMLR Science, In press

  13. Acknowledgements CEBC - CNRS Fundings and Partnership Terres Australes et Antarctiques Françaises Armements de pêche à la légine réunionais Muséum National d’Histoire Naturelle de Paris Coordinators Dr Christophe Guinet Pr. Guy Duhamel Thierry Clot Data Collection Fishery observers and field workers of Possession Island – special thanks to Nicolas Gasco Help in analyses M. Authier, M. Viviant, C. Barbraud, D. Pardo, D. Pinaud, J. Vacquie Garcia, T. Jeaniard Dudot, P.Monestiez Photographers AUBERT Jean Luc; BARRETT-LENNARD Lance; BEILLOEIL; BELBEYC'H Bruno; BERTHET Philippe; BERTRAND Geoffrey; BLANCHARD Pierrick; BOITEAU Christophe; BONNET Joël; BOST Charles-André; BURLE Marie-Hélène; CARCAILLET Christopher; CARDOT Gilles; CHEVRIER Claude; DE STEPHANIS Renaud; DERVAUX Antoine; DESMARET Rolland; DESPIN Bernard; DONDELINGER Caroline; DOREMUS Ghislain; DUFRENE Rémy; FERNANDEZ Eric; FOURNIER Jean-Charles; GASCO Nicolas GAUTHIER-CLERC Michel; GOUEDARD Yvon; GUINET Christophe; HANDRICH Yves; HANUISE Nicolas; HOARAU Eric; LANGUENOU Roger; LE CORRE Yann; LEGRAN Jérôme; LEMARCHAN Christian; LEQUETTE Benoît; LERIDON Jean; LEROUX Eric; LESCAROUX Jean-Michel; LOUBON Maxime; MAISON Jérome; MANGIN Stéphane; MANILEVE Patrick; MARECHAL Pierre; MELLEE Jean-Luc; MOURIES Jacques; NOORKHAN Alain; NOYAN Patrick; PAULIN Rémy; PAWLOWSKI Frédéric; PERROT Yohann; PETER Jean; RIDOUX Vincent; RINGOT Frédéric; SCHWEBEL Luc; SORIN Dominique; STENBERGER Ludovic;THERON Franck; TIXIER Paul; VERLAND Henri; VERMANDE Hugues; VILLEMIN Catherine; WEIMERSKIRCH Henri

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