@inproceedings{fdi:010065858, title = {{P}referred habitat of tropical tuna species in the {E}astern {A}tlantic and {W}estern {I}ndian {O}ceans : a comparative analysis between {FAD}-associated and free-swimming schools}, author = {{D}ruon, {J}.{N}. and {C}hassot, {E}mmanuel and {F}loch, {L}aurent and {M}aufroy, {A}lexandra}, editor = {}, language = {{ENG}}, abstract = {{A}n ecological niche modelling ({ENM}) approach was developed to describe the suitable habitat of skipjack ({SKJ}) and juvenile yellowfin ({YFT}) tuna in the {T}ropical {A}tlantic and {W}est {I}ndian {O}ceans. {T}he environmental envelop of the potential habitat in each ocean was defined using occurrence data independently of the fishing mode and derived from purse seine fishing sets of the {F}rench fleet during 1997-2014. {D}aily satellite-derived chlorophyll-a content ({CHL}) and fronts ({CHL} gradient) were used as a proxy for food availability while circulation model derived-sea surface temperature, salinity, height anomaly, current and oxygen as well as the mixed layer depth contributed to identify the physical suitable conditions of each species. {O}nly the cluster that showed no {CHL} front was excluded for the parameterization in order to enhance the favourable feeding habitat. {I}n a second step, the distances of both the free swimming schools ({FSC}) and schools associated with drifting {F}ishing {A}ggregating {D}evices ({FAD}s) to the closest potential habitat were computed and compared. {T}he results highlighted (i) high spatial seasonality of both the simulated feeding habitat and tuna populations in the {I}ndian {O}cean compared to the tropical {A}tlantic, (ii) major differences between both oceans regarding the distance of {FAD} catches to the potential habitat with median values above 200 km in the {A}tlantic and below 16 km in the {I}ndian {O}cean, while equivalent distances for {FSC} were observed for both species and areas (below 2 km and 43 km respectively) in agreement with stomach content analysis, (iii) an increased rate of {FAD} fishing operations in the decade from 2003 to 2013 (up to about 70% in the {A}tlantic and 96% in the {I}ndian {O}cean) occurring mostly in poor environments in the tropical {A}tlantic while frequently in relatively productive waters in the {I}ndian {O}cean (except east of 58°{N}) as well as an overall 300% increase of juvenile {YFT} presence in both ocean sets and (iv) a recent intensification of fishing effort from {M}arch to {M}ay in the {M}ozambique {C}hannel in agreement with an increase of favourable habitat, while no effort of that fleet occurred in the open waters off the {G}abon upwelling (from 1°{N} to 5°{S} and {E}ast of 17°{W}) from {M}ay to {S}eptember where favourable habitat was enhanced by the model. {I}n all cases the seasonal maximum number of fishing sets corresponded to the minimum extent of potential habitat, which commonly varied by 30% from year to year. {O}verall, this comparative analysis emphasizes the strong attraction of tropical tuna species to floating objects although feeding opportunities may vary considerably depending on hydrographic regimes and on the dynamics of productive habitats.}, keywords = {{OCEAN} {INDIEN} ; {ATLANTIQUE}}, numero = {{IOTC}-2015-{WPTT}17-31}, pages = {23}, booktitle = {17{\`e}me groupe de travail sur les thons tropicaux}, year = {2015}, URL = {https://www.documentation.ird.fr/hor/fdi:010065858}, }