Figure 7.1.1. Individual target strength (TS) from 38 kHz data collected during
a 1997 field study in the Gulf of Maine. The TS distribution centered at -62
dB was mainly from euphausiids, while the TS distribution centered at -37
dB was contributed primarily from Atlantic herring. The higher TS measurements
were most likely blue sharks that were observed feeding on herring, or from
possibly cod and haddock near bottom.
Figure 7.1.2. Individual target strength (TS) data collected around (5 nmi
before and after) and during a midwater trawl deployment that captured predominantly
(more than 95% of catch) Atlantic herring during the 2000 Atlantic Herring
Hydroacoustic Survey. Mean TS for this distribution is -42.3 dB, however further
analyses are required to separate TS values that are not from herring.
Figure 7.1.3. About 98% of the filtered potential false individual target
strength measurements (narrow bars) were removed from the unfiltered (wide
bars) in-situ 38 kHz target strength measurements collected during the 1997
Bioacoustic Study. The multifrequency (38 and 120 kHz) filtering algorithm
to remove potential false individual targets is described in Demer et al.
(1999).
Figure 7.1.4. About 99% of the filtered potential false individual target
strength measurements (narrow bars) were removed from the unfiltered (wide
bars) in-situ 120 kHz target strength measurements collected during the 1997
Bioacoustic Study. The multifrequency (38 and 120 kHz) filtering algorithm
to remove potential false individual targets is described in Demer et al.
(1999).