Publications des scientifiques de l'IRD

Receveur A., Menkès Christophe, Allain V., Lebourges Dhaussy Anne, Nerini D., Mangeas Morgan, Ménard Frédéric. (2020). Seasonal and spatial variability in the vertical distribution of pelagic forage fauna in the Southwest Pacific. Deep-Sea Research Part II : Topical Studies in Oceanography, 175, 104655 [16 p.]. ISSN 0967-0645.

Titre du document
Seasonal and spatial variability in the vertical distribution of pelagic forage fauna in the Southwest Pacific
Année de publication
2020
Type de document
Article référencé dans le Web of Science WOS:000554017400002
Auteurs
Receveur A., Menkès Christophe, Allain V., Lebourges Dhaussy Anne, Nerini D., Mangeas Morgan, Ménard Frédéric
Source
Deep-Sea Research Part II : Topical Studies in Oceanography, 2020, 175, 104655 [16 p.] ISSN 0967-0645
Acoustic data are an invaluable source of information for characterizing the distribution and abundance of mid-trophic level organisms (MTLOs) in the ocean. These organisms play a key role in the ecosystem as prey of top predators and as predators of lower trophic level organisms, as well as in carbon export from the surface into deeper waters. This study used 38 kHz-EK60 acoustic echosounder data from six cruises spanning 2011-2017 to explore the seasonal and spatial variability in the vertical distribution of MTLOs' from 10 to 600 m in the New Caledonian (South Pacific) Exclusive Economic Zone. A total of 16715 acoustic vertical profiles of acoustic backscattering strength were clustered into homogeneous groups. Two small shallow scattering layers (SSLs) between 0 and 100 m, and one large deep scattering layer (DSL) at around 550 m depth, characterized the mean vertical distribution of MTLOs. A machine-learning model (eXtreme Gradient tree Boosting algorithm, XGBoost) was fitted to explain the acoustic profile clusters with environmental variables as predictors. Sun inclination was the most important factor in structuring the vertical profile shapes due to the diel vertical migration signal, followed by the mean oxygen value of the top 600 m. Bathymetry, euphotic depth, 0-600 m mean temperature and SST were the next most significant variables. Isotherm depth, surface chlorophylDa, wind, and mean salinity had a lower influence on the shape of the vertical profiles. The model was then used to construct vertical echograms at the scale of the New Caledonian EEZ, showing an accuracy up to 87% in cross validation. Across the EEZ, the shape of vertical acoustic profiles were comparable, though layer echo intensities varied spatially with a marked north-south gradient that remained relatively constant seasonally. The vertically-averaged acoustic values were characterized by a maximum to the south of the EEZ in summer, mainly driven by high oxygen values as well as shallow euphotic depth. We also estimated a migrant proportion between day DSL and night SSL of about 78%. Our methodology offers a promising approach for analyzing the control of the environment on the vertical distribution of MTLOs for other oceanic provinces, while also providing a framework to investigate the corresponding trophic interactions between MTLOs and their predators feeding at different depths and times. Moreover, our findings stress the need to consolidate knowledge on species composition to optimize acoustic data interpretation.
Plan de classement
Limnologie physique / Océanographie physique [032] ; Ecologie, systèmes aquatiques [036]
Description Géographique
NOUVELLE CALEDONIE ; PACIFIQUE
Localisation
Fonds IRD [F B010079388]
Identifiant IRD
fdi:010079388
Contact