Fish Population and Behavior Revealed by Instantaneous Continental Shelf-Scale Imaging

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Science  03 Feb 2006:
Vol. 311, Issue 5761, pp. 660-663
DOI: 10.1126/science.1121756

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  1. Fig. 1.

    Two instantaneous areal density images of fish shoals near the continental shelf edge obtained by ocean acoustic waveguide remote sensing (OAWRS) at (A) 09:32 EDT, 14 May 2003, and (B) 08:38 EDT, 15 May 2003, each acquired within 40 s. νA is shown in color. The moored source (the white star) is the coordinate origin in all figures at 39.0563°N, 73.0365°W. The towed horizontal receiving array (the white diamond) has 2.6° azimuthal resolution at array broadside. The range resolution is 30 m after averaging (14). The forward propagation of sound masks imaging inside the gray ellipse surrounding the source and receiver. The positive vertical axis points north. Depth contours are indicated by dashed lines. In (A) and (B), the continental shelf edge begins at roughly the 100-m contour. (C) Spatial frequency spectra, based on scores of instantaneous OAWRS images of νA, for cases where a large shoal is present and only small scattered fish groups are present. A consistent spectral power law of spatial frequency to the –1.5 is observed.

  2. Fig. 2.

    A comparison of OAWRS with conventional fish-finding sonar (CFFS). (A to D) A sequence of instantaneous OAWRS areal density (fish/m2) images taken roughly 10 min apart, starting at 11:59:05 EDT on 14 May 2003, is shown. The color bar is the same as in Fig. 1. The corresponding CFFS transect is overlain in light blue, with the CFFS position for the given OAWRS image indicated by a circle. The white dashed line is the 100-m depth contour. (E) Range-depth profile of fish volumetric density (fish/m3) measured by CFFS along the transect shown in (A) to (D). White bars (in the lower black region below the sea floor) correspond to typical time-space points α, β, and γ, where both systems co-register dense fish groups [(A) to (C)]; the gray bar corresponds to point δ in (D), where neither system registers dense fish groups.

  3. Fig. 3.

    Evolution of a fish shoal from morning to evening from OAWRS imagery and a time series on 14 May 2003. (A to D) Four instantaneous OAWRS images or snapshots illustrating morning consolidation and afternoon fragmentation of the shoal. The color bar is the same as in Fig. 1. Vertical arrows indicate snapshot times. (E) A time series of population within the area shown in (A) to (D) for νA within each of the thresholds specified. Gaps in the time series are due to towed-array turns. (F) Area occupied by a consolidated shoal or its two largest fragments for νA > νshoal = 0.2 fish/m2. (G) The internal coherence area is the area within 1/e of the 2D autocorrelation peak of instantaneous OAWRS fish density within the shoal or fragment. The centroids of two particular population centers within the shoal are indicated by the circle and the triangle in (A) to (D). (H) Relative speeds between the centroids of the two population centers shown in (A) to (D), with mean (blue circle) and standard deviation (bars) shown for each track.