Fig 1.
Study area in the north-western Bay of Biscay (average depth: 110 m).
Table 1.
Echosounders settings.
Table 2.
Characteristics of the nets used for biological sampling.
Fig 2.
Pulse compressed Sv echograms recorded during net tows.
The vertical blackline separate data collected on May, 27th and 28th. Blue and red horizontal lines represent the boundaries of surface and deep sampled layers, respectively.
Table 3.
Scattering model parameters used for Fluid-like organisms.
SD: Standard Deviation.
Table 4.
Scattering model parameters used for Gas Bearing organisms.
Table 5.
Statistical distributions for the model parameters used in the uncertainty analysis.
μ: mean, SD: standard deviation, 5% and 95% quantiles of the distribution: Confidence Interval (0.05-0.95) the, L/2a: length/width ratio, L/a length/half-width ratio.
Table 6.
Composition and length of each layer main scatterers.
SD: Standard Deviation.
Fig 3.
EM clustering results for (a) the surface layer and (b) the deep layer.
Upper panels: echo-integration cells belongings to cluster; left of vertical black line: data collected on May, 27th, right of black line: data collected on May, 28th. Middle panel: net trajectories (black lines). Lower panel: median volume backscattering strength spectra at frequency f (Sv(f)) in the whole depth layer (red and blue curve with 25% and 75% quantiles confidence intervals) and in each cluster.
Fig 4.
Forward approach results: modeled frequency spectra (Sv(f)) are represented in the left column (Fig (a) for surface layer, (c) for deep layer). Coloured areas: confidence intervals (5th and 95th percentiles of uncertainty analysis results). Measured Sv(f) (red or blue lines) and predicted Sv(f) (black line) frequency spectra are represented in the right column, (Fig (b) for surface layer,(d) for deep layer). Coloured areas around measured Sv(f): confidence intervals (25th and 75th percentiles). Volume backscattering strength Sv level at 18, 38, 70, 120, 200 and 333 kHz and their 25th and 75th percentiles confidence intervals are represented by crosses.