The Danish fisheries c.1450-1800. Medieval and early modern ...

and the North Sea in the west was breached by a flood in 1624 and 1825. We know that the
fish catches went up in the years immediately after the second breach, and that may also have
happened in the 1620s. However, by 1630 and 1832 the fisheries were reported to be much
depressed. The herring, which was accustomed to brackish water, was probably severely
reduced with the intrusion of salt water. In the 1630s, the dune barrier was built up by the
natural sand drift along the North Sea coast, and the herring stock regained strength. 34 The
process would perhaps have repeated itself in the nineteenth century had it not been for
dredging and coastal works to keep the fiord open. The decadal cycle of the fishery which
may be detected from the 1670-1750 series may also wholly be explained as a biological
pattern, while the depression of the Limfjord fishery in the late eighteenth century may partly
be explained as an economic result of overwhelming Bohuslen exports in the 1760s, but we
should note the long-term decline which had begun already by the 1730s.
The periodicity of the Bohuslen herring implies that environmental forcing was the
major underlying factor, while it has been argued above that the sudden cessation of the
fishery in 1590 was have been linked to market factors. The alternating cycles of North
European pelagic stocks seem to be correllated to the North Atlantic Oscillation, and the
historical data for the Bohuslen herring stock is one of the best examples of this correllation.
The most probable explanation, which parallels the experience from the nineteenth-century
herring fishery on the same resource, 35 is that the herring shoals preferred spawning grounds
outside the reach of the inshore fishermen. If, because of a change in salt concentration,
spawning suddenly took place in the middle of the Skagerrak rather than in the sheltered
archipelago of Bohuslen, the shorebound Danish and Norwegian fishermen may have found it
impossible to catch the herring. In order to go deep-sea fishing they would have needed
34 Danske Magazin 3:4, 329-332.
35 See Holm, Kystfolk, chapter 7.