Fish was an important element in the diets of the people of Viking Age Britain. Other than the odd times during the winter when the rivers or lakes froze, the sea and rivers were an abundant source of regular fresh food. There was no waiting for things to ripen, or grow to an age when they were large enough to slaughter. Even in winter, as long as the weather was favourable, you could still fish. The proximity of a site to water dictated how much was eaten in the community. In excavations from Hedeby in Northern Germany, where the site was on the shore of a low lying fjord, the fish bones excavated could be divided into three general categories - sea fish, fish that were at home in sea or fresh water and purely freshwater species - with at least 26 separate species recorded. Of the identified varieties of fish, there were large quantities of: Cod, Herring, Plaice and Garfish. From the brackish zone there were: Salmon, Sea Trout and Eels, and finally from the fresh water species were: Pike, Perch, Chubb and Carp.
The volume of each variety of fish works out like this:
Herring 38%, Perch 25%, Pike 11%, Carp 11%, Flatfish 7%, other 8%
Many of the fish identified, would today be regarded as not worth eating as they were either too bony, or taste far too much of mud. This was never a real problem for people of the period. Apart from fresh catches, fish, when caught in sufficient numbers were either air dried or smoked to preserve them. The kipper which is a filleted and smoked herring has been a part of peoples' diet for an exceedingly long time - certainly, smoking as a means of preservation was being used in the Iron age. After preserving, either the kippers or the air dried fish could be placed into barrels that were not water tight, called dry casks. The contents consisted of a layer of sawdust, salt and dried fish; then more sawdust, salt and so on until the cask is full, whereupon it was sealed. The fish inside, if kept dry, would last for months. Salt fish can still be bought today, although it needs soaking to get rid of the salt before it can be added to the cooking.
The Vikings had what we would call some very catholic tastes. One traditional recipe from Iceland is for Cod boiled in Whey. Another is for Greenland Shark that is buried for several months and uses the urea in the muscles to help rot down the flesh. I personally haven't gone any further into what they did with the remains as a meal as yet. The Anglo Saxons regarded dolphins and other porpoises as fish and therefore allowed their consumption during lent.
Not mentioned are shell fish, which were collected just as regularly as fish were caught. The habitats that shell fish live in have a huge bearing on their availability, as only a few places have mud flats that are ideal for Whelks, Cockles etc, whereas a lot of the Scandinavian coasts are rocky. Rocky coasts provide habitats for Limpets, Mussels and Oysters. Crabs, Lobsters and fresh water Crayfish were also fished for, however there is little evidence as to what kind of traps were used.
The build up of villages into towns had a direct effect upon the quality of the water, particularly where places were situated on rivers. Due to the primitive living conditions, and the use of open sewers, pollutants soon got into the water courses affecting water quality. One good example of this comes from Canterbury. The middens from the city around the 8th century are full of shells from fresh water oysters. As time went by and the population crept up, the subsequent increase in pollution levels caused the oyster population to crash and finally die out all together. The river Ouse in York suffered from similar problems associated with a growing population and inadequate sanitation and even by the eleventh century fish populations were being affected by pollutants in the water. Abundance was sometimes a problem too. In the Middle Ages, Salmon in the rivers Tyne and Tees were caught in huge numbers, so much so that they became a particular part of the diet of not just the rich, but the poor as well. Apprentices in a number of guilds complained of being fed Salmon too regularly.