This work describes results from two recent field programs exploring t
he feasibility of high-frequency, side-looking sonar systems for fish
detection in shallow waters. The first project in September 1995 was a
imed at detection of migratory salmon in the Fraser River near Mission
, British Columbia. Using a fixed installation of 100-kHz sidescans lo
oking transverse to the river flow from one bank, individual salmon ta
rgets were observed at ranges up to 200 m in waters 4-12 m deep. A sec
ond experiment in May 1996 sought to image spawning herring schools us
ing towed and azimuthally scanning 100 and 330 kHz sidescans in a shal
low marine region near Escuminac, New Brunswick. Herring schools were
successfully imaged at ranges up to 150 m in waters only 3-4 m deep. I
n both cases, the fish targets were identified and quantified against
a background of acoustic reverberation using manual recognition techni
ques. Example sonograms from both experiments will be discussed. In bo
th experiments the detection efficiency diminished with range due to i
nterference from surface and bottom boundary back-scattering. Occasion
al, strong interference from boat traffic and breaking-wave induced bu
bble layers drastically reduced fish detection capability. (C) 1998 El
sevier Science B.V.