Along the mudflats on the South Essex coast an aerial survey identified a massive complex of wooden fish-traps, comprising up to 13,000 timber posts, located ½ a mile out to sea. A more detailed investigation carried out by boat has revealed a dozen lines of timber - some of them more than half a mile long- in the Blackwater estuary, 15 miles south of Colchester, dating from the 7th to 10th centuries AD. The timbers were the uprights of wattle fences, the complex containing up to 100,000 square feet or 30,500 square metres of fencing, some of which still survives.
The fences - laid out in a series of V-shapes - were used to funnel the outgoing tide, and its fish, into nets at the apexes. They would have yielded several hundred thousand fish per year: far too many to supply a single community, suggesting that the trapping was carried out for commercial purposes. The fish would have been salted, dried and, presumably, sold to communities in south-east England. It is not known who maintained these traps but, just seven miles away is Bradwell-on-Sea, where one of Englands earliest monasteries stands, founded in 654 AD. Across the Thames estuary from the Blackwater lies the estuary of the River Medway with similar terrain features. Along the Medway estuary, although no extensive finds such has been found on the Blackwater, references to 'fish factories' are included in the Domesday Book. One wonders! 12
It is likely that the trap was flat bottomed to allow it to lie on the river or sea bed without rolling with the current or tide. For eels it would need to be baited with a dead fish, this would attract the carnivorous eel into the funnel and once inside, they would find it difficult to escape. Single chambered traps may also have been used by the early medieval fisherman; these would have been something akin to the salmon putchers used earlier this century in Scotland and on the Severn River. The main advantage of these traps was that smaller fish could be caught, there was little danger of the fish swimming away from them as in the case with a net and they were relatively easy to maintain.
The traps themselves would be made from willow 'withies' that had been cultivated for at least three years. Today there are withy beds in the Southwest that produce willow withies in white, buff and brown. White withies are produced by stripping the bark away, the buff has been boiled with its bark on and then the bark then removed and the browns are the withies complete with bark. In the early medieval period the majority of the basket work was functional and there was no need to add extra work to the making of fish traps and baskets: brown withies would have been the most common. To weave the withies they would need to be soaked so as to make them pliable, they would need to be left to soak overnight to enable the surface water to penetrate to the pith of each withy.