@inproceedings{fdi:010078275,
  title = {{M}icronektonic acoustic density variations in {G}uinea {C}urrent {L}arge {M}arine {E}cosystem continental shelf from 1999 to 2006 [r{\'e}sum{\'e} de poster]},
  author = {{K}ouassi, {A}.{M}. and {B}ehagle, {N}olwenn and {K}on{\'e}, {V}. and {P}errot, {Y}annick and {T}iedemann, {M}. and {M}ouget, {A}nne and {M}igayrou, {C}. and {K}rakstad, {J}.{O}. and {K}anga, {D}.{K}. and {K}ouadio, {B}. and {D}iogoul, {N}. and {B}rehmer, {P}atrice},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he {G}uinea {C}urrent {L}arge {M}arine {E}cosystem ({GCLME}) extends from {B}issagos {I}sland ({G}uinea {B}issau) in the north (11°{N}, 16°{W}) to {C}ape {L}opez ({G}abon) in the south (0°{S}, 8°{E}) and includes the study zone, from 4°{N}, 8°{W} to 6°{N}, 3°{E}. {A}coustic data were recorded with a 38 k{H}z echosounder, from 10 to 500 m depth over 7 surveys, 6 were selected here, totalling 16 618 nmi from 1999 to 2006. {T}o get homogenous data, (i) only off-upwelling season surveys ({A}pril to {S}eptember) were studied and (ii) only continental shelf data were considered (10-150 m). {T}he mean volume backscattering strength ({S}v in d{B}) was used as a micronektonic biomass proxy to assess its spatial inter-annual variability. {D}iel transition periods were removed from analyses to avoid micronektonic density changes bias due to diel vertical migrations. {D}ata were echointegrated at a spatial resolution of 0,1 nmi*1 m depth using {M}atecho tool ({P}errot et al., 2018). (i) {O}n horizontal dimension, the variability in annual micronektonic densities was assessed using the mean {S}v value for each 0,1 nmi {E}lementary {S}ample {U}nit ({ESU}). (ii) {O}n vertical dimension, the water column variation (%) filled by micronektonic acoustic layer (filling rate) across years was estimated using a linear regression and the change of micronektonic spatial structure between day and night was assessed using the mean {S}v value for each 1 m depth step. {GCLME} have a narrow continental shelf vs. other {A}frican {A}tlantic {LME}s. {N}o significant change of micronektonic biomass proxy has been observed from 1999 to 2006 in this study ({F}ig. 1). {A}s expected, a difference is observed in the vertical micronektonic acoustic density between day and night ({F}ig. 3). {H}owever, there is a paradoxical process, indeed there is an increase in {S}v during nighttime. {T}wo hypotheses are proposed: (i) the increase in density could be explained by an offshore horizontal diel migration or (ii) a very high contribution of the micronektonic density occurring in surface (0-10 m) is suspected, which corresponds to the blind zone of the research vessel. {A}ccording to the new descriptor “water column filling rate”, a significant change in the system is reported. {I}ndeed there is an increase in five years. {F}uture investigations should focus on this interesting phenomenon, which could be link to an effect of global change. {W}e have to take care that such increase could also inform on a major change in the trophic web in this part of the {GCLME}. {T}hese findings can be interpreted as an early warning signal and encourage for future study.},
  keywords = {{AFRIQUE} {CENTRALE} ; {GUINEE} {BISSAU} ; {GABON} ; {ATLANTIQUE} ; {BISSAGOS} {ILE} ; {LOPEZ} {CAP}},
  numero = {},
  pages = {144--145},
  booktitle = {{I}nternational conference {ICAWA} 2017 and 2018 : extended book of abstract : the {AWA} project : ecosystem approach to the management of fisheries and the marine environment in {W}est {A}frican waters},
  year = {2019},
  ISBN = {978-9553602-0-06},
  URL = {https://www.documentation.ird.fr/hor/fdi:010078275},
}