Cs. Rose et Ep. Nunnallee, A STUDY OF CHANGES IN GROUNDFISH TRAWL CATCHING EFFICIENCY DUE TO DIFFERENCES IN OPERATING WIDTH, AND MEASURES TO REDUCE WIDTH VARIATION, Fisheries research, 36(2-3), 1998, pp. 139-147
The influence of trawl width on the ability of a survey trawl to captu
re groundfish was tested by comparing catch rates between paired tows
with and without a constraint line that reduced the operating width of
the trawl. The vertical distribution of fish near and above the seafl
oor was recorded with an echo sounder to test for the incidence of fis
h diving into the path of the trawl during the tows. Arrowtooth flound
er (Atheresthes stomias), flathead sole (Hippoglossoides elassodon) an
d walleye pollock (Theragra chalcogramma) were captured at higher rate
s (fish per area swept) by a survey trawl fished in the restricted (na
rrow) configuration. The greatest difference occurred for pollock. The
difference in catch rates was consistent across size groups within ea
ch species. Correlations detected between catch rates of pollock and e
cho-integration values for targets well above the trawl height indicat
ed that some of these fish may have been diving from midwater into the
path of the trawl. Differences between the correlation patterns with
and without constraint lines indicate that the diving behavior may be
affected by the presence of the line. Published by Elsevier Science B.
V.