Mv. Trevorrow et Rr. Claytor, DETECTION OF ATLANTIC HERRING (CLUPEA-HARENGUS) SCHOOLS IN SHALLOW WATERS USING HIGH-FREQUENCY SIDESCAN SONARS, Canadian journal of fisheries and aquatic sciences, 55(6), 1998, pp. 1419-1429
This work examines results from field trials in April and May 1996 exp
loring the feasibility for estimating spawning Atlantic herring (Clupe
a harengus) abundance using a 330-kHz sidescan sonar in a shallow coas
tal region near Escuminac, New Brunswick. Herring schools were observe
d using both towed and fixed-location, azimuthally scanning techniques
at ranges up to 100 m in water depths of 3-6 m. The schools were typi
cally linear in shape, with lengths of 100-280 m, thickness of 4-14 m,
and peak acoustic target strength near -12 dB. Using acoustic ray-tra
cing analysis, surface-and bottom-reflected multipaths from an ensembl
e of targets an shown to increase the echo amplitude and reverberation
time, producing large overestimates (4-27 times actual) in herring de
nsities when using echo-integration. Using the acoustic simulations to
compensate for this reflection focusing, average population densities
near 11.m(-3) were estimated, with the schools comprising 10 900 - 10
3 000 individuals. These total school sizes and densities were consist
ent with expectations for spawning herring.