THE BOTTOM FAUNA OF THE BLACKWATER ESTUARY 17
The procedures adopted by the surveys described herein were
basically those used in the earlier survey (see Barnes and Cough-
Ian, 1971). The use of a dredge, however, proved impossible, it
having been the practice during the past years for fishermen to
dump "rubbish" trawled on the adjacent fishing grounds into the
region near the barrier wall. After the first few attempts at
dredging resulted in gear fouled by scrap metal, further attempts
were abandoned. Faunal samples were obtained, therefore, en-
tirely by the use of a 0.lm2 van Veen grab. A 0.5m2 Baird grab
and a 5.0cm internal-diameter gravity corer, of barrel length
10m, were used on occasion to determine the nature of the sub-
strate. The grab frequently failed to close, or surfaced with
loads which could not be brought aboard as a result of the dump-
ing, but satisfactory samples were eventually obtained from all
stations.
A basic grid of twenty-four sampling points was used (Fig. 2).
Six of the points were situated outside the immediate vicinity of
the barrier wall and were used as approximate controls for the
remaining stations. Three of the six were sited about 300m to
the east of the eastern end of the wall and three a similar dis-
tance west of the western end. The central stations in each
Fig. 2. Sketch-map of the study area showing the grid of sampling
stations
group of three were in direct line with the wall, whilst the outer
stations were about 100m to the north and south of that axis
respectively.
The remaining eighteen stations were arranged in six lines
of three in parallel with the wall, three lines being to the north