What is a finnock?
Finnock (otherwise locally named whitling, herling, school peal, harvesters etc) are small sea trout in their first year after smolt migration, often found in the estuaries or lower areas of rivers. They do not necessarily remain faithful to their natal areas at this stage, instead they range widely up and down coasts, moving into and out of fresh water with the tides. Often congregating at “choke points” around estuaries, they are highly vulnerable to excessive angling pressure, as well as natural predation. Many of these attractive and energetic fish may over-winter in fresh water while still immature, making only limited growth until they return to the sea properly in spring. Why they do this and lose potential growing time utilising richer marine feeding is unknown. It seems unlikely to be an avoidance response to osmotic problems because salinity tolerance trials have shown that even small post-smolt sea trout have no apparent problems coping with full-strength seawater, in summer or winter. While finnock are characteristic of the rivers further north, the prolific sea trout rivers of south-east Scotland and north-east England largely lack this early-returning itinerant form. [The term “Whitling” is also used on the River Till in Northumberland, a lower tributary of the Tweed. Here it refers to small sea trout, mostly of 1+ sea winters]. Tagging has shown that many of the post-smolt trout from the Rivers Tweed and Coquet move down the North Sea and remain there during winter, taking full advantage of the rich potential for feeding. These further-travelling, faster-growing sea trout appeared historically in netting catches off the Northumberland and Yorkshire coasts, then East Anglia, Holland and Denmark, before returning to their native rivers to spawn. The erratic movements of finnock between rivers in general and the extensive migrations of sea trout in the southern North Sea indicate significant mixing of stocks during the marine phase, raising complex issues for their conservation and fishery management.