'Royal College of Obstetricians & Gynaecologists (RCOG)'
Abstract
An application of a new automated fish counting device – the
Riverwatcher System (RW) – was used to monitor upstream
fish movements in a pool-and-weir fish pass in the River
Zeˆ zere, Portugal, for 141 days from June 2002 to May 2003.
Fish populations were also collected downstream using multimesh
gillnets (5 different mesh sizes ranging from 30 mm to
85 mm knot to knot; ratio between mesh sizes of about 1.30)
and electrofishing for comparison with fish records produced
by the RW. More than 3000 individual Iberian nase Chondrostoma
polylepis ascended the fish pass and moved through the
RW during the study period. However, only 18% of the
records produced by the RW contained silhouettes similar to
fish; no individual smaller than 15 cm TL was recorded by the
counter. Most seasonal movements (73.9%) occurred in spring
and were associated with reproduction. Displacements seemed
to occur independently of time of day. Water temperature
(range: 12–22 C) was the only significant environmental
variable (P < 0.01) influencing upstream movements of this
species. Further development of hardware and software will be
necessary to improve performance of the counter, particularly
in Mediterranean rivers, where more turbid waters and a
greater proportion of small-size species are presen