THE FAUNA OF THE CROUCH/ROACH ESTUARY 131
A Contribution to the Fauna of the
Crouch/Roach Estuary
By Alan Howard
Ministry of Agriculture, Fisheries and Food
Fisheries Laboratory, Remembrance Avenue,
Burnham-on-Crouch, Essex CM0 8HA
Introduction
The estuaries of the Essex rivers Crouch and Roach are comparatively
unspoilt, with a correspondingly diverse fauna. Recent plans for the con-
struction of an airport/seaport on Maplin Sands to be followed by wide-
spread urban development threatened to make radical changes in the area.
A study was therefore initiated to record the present fauna, from a combin-
ation of trawl and grab sampling sites, to give a basis for comparison if
the development occurred.
This threat of development in the area has since receded, and so identi-
fication of the animals obtained by grabbing has been postponed. However,
the trawl contents were identified on the boat or soon after collection and
so can be presented here.
The estuary can be considered as an extension of the sea reaching some
24 kilometres inland to Battlesbridge. Depth and width of the channel at
its mouth are approximately 13 metres and 2 kilometres respectively,
reducing to saltings at the head of the estuary. The normal tidal range in
the area is up to 6 metres. Routine records kept at the Burnham Laboratory
show that the average annual range of bottom water temperature is 1°C-
22°C, while the bottom salinities range from approximately 30‰ at the
mouth to 10‰ in the headwaters. There can be great variation in the salin-
ity of surface samples, especially when neap tides accompany a rain
deluge.
Method
The bottom fauna was sampled by a 4 metre shrimp beam trawl fitted
with two extra 'tickler chains'. This was towed with the tide between the
fixed points shown in Figure 1. The duration of each haul was approxi-
mately 30 minutes. Familiar animals were identified and counted, or
estimated by volume constants on the boat. The others were taken to the
laboratory for identification using the keys of Allen (1967) for decapod
crustaceans, Millar (1970) for ascidians and Wheeler (1969) for fish. The
Porifera were identified at the British Museum, while the Amphipods and
Pycnogonids have not been classified beyond their Order and Class
respectively. The survey was conducted four times during the autumn,
winter, spring and summer of 1973-1974. It was repeated during October
1974, to indicate the variability of the results from year to year.