@inproceedings{fdi:010063743,
  title = {{S}kipjack tuna {CPUE} trends using alternative indices from the {F}rench purse seine logbooks},
  author = {{M}arsac, {F}rancis and {F}loch, {L}aurent},
  editor = {},
  language = {{ENG}},
  abstract = {{W}e used the {F}rench purse seine data to examine the trend of skipjack {CPUE}s for the period 1984-2013. {O}nly sets made on drifting objects (logs and fish aggregating devices –{FAD}s) are used in this analysis. {S}ensitivity tests were performed to evaluate the effect of the size of the core area in the north equatorial area (0-13{N}/45’70{E}) as well as effort minimal thresholds, on {CPUE} estimates (filtered nominal indices based on the catch per set). {N}o significant effect was noted suggesting that the north equatorial area, as a whole, is a pertinent skipjack core area. {A} standardization procedure was applied to datasets based on {CPUE}s aggregated by 1°longitude/0.33° latitude and by month, to which corresponding environmental data such as the depth of the mixed layer, the sea surface anomaly, the speed of the current and the chlorophyll concentration were added. {G}eneralized additive models ({GAM}s) were used to explore the shape of relationships with fishery-derived and environmental covariates, and undertake transformation in the dataset used by generalized linear models ({GLM}s). {S}even models with various assumptions were tested. {T}hey denote a clear skipjack {CPUE} decline since 2002, with a steeper rate of decline since 2009. {W}e suggest that the massive deployment of {FAD}s during the 1990s and the development of efficient {FAD} fishing tactics have likely contributed to such decline, as more than 60% of skipjack is caught on {FAD}s. {H}owever, environmental fluctuations are also at stake in such decline and notably the chlorophyll concentration which reflects the productivity level at the base of the food chain. {T}he surface chlorophyll concentration has been anomalously low in the {S}omali {B}asin since 2006 and this could lead to detrimental foraging conditions for the upper trophic levels, or trigger spatial shift of the population in search of more productive areas. {T}he biological and ecological processes associated to this decline would deserve more research. {H}owever, the fact that a sustained {CPUE} decline for skipjack has been occurring since 2002 could become a concern for the conservation of this stock.},
  keywords = {{PECHE} {THONIERE} ; {STOCK} ; {SENNEUR} ; {DISPOSITIF} {DE} {CONCENTRATION} {DES} {POISSONS} ; {EFFORT} {DE} {PECHE} ; {CAPTURE} ; {CHLOROPHYLLE} ; {VARIATION} {PLURIANNUELLE} ; {OCEAN} {INDIEN} ; {FRANCE}},
  numero = {{IOTC}-2014-{WPTT}16-41},
  pages = {32},
  booktitle = {16{\`e}me groupe de travail sur les thons tropicaux},
  year = {2014},
  URL = {https://www.documentation.ird.fr/hor/fdi:010063743},
}