Can Historical Names & Fishers’ Knowledge Help to Reconstruct Lakes?

Reconstructing the historical distribution of local Brown trout populations is of great importance. Information of what has actually been lost and its causes is necessary for rebuilding natural lake ecosystems and recreational fisheries, as well as monitoring future changes. Older fishermen and local fishing right owners in 63 privately governed fishery management organizations (FMOs) in Northern Sweden were interviewed, focusing on current species distribution, stocking, introductions and extinctions in 1509 lakes. Names were collected for each lake from modern and historical maps. Historical archives concerning fish species distribution and stocking were also compiled. Brown trout lake candidates were surveyed with multimesh-sized gillnets or other methods. Observations of bottom substrate confirmed or ruled out existence of proper habitat conditions for spawning. Chemical, physical and biological anthropogenic impacts were assessed by archival data and limnological surveys over 20 years. Information gathered from a number of sources and methods allowed for comprehensive validation of lake name evidence and interviews. All data were temporally as well as geographically referenced and stored in a GIS-linked database. One third of all lakes with historical or present Brown trout populations had Rö, or other dialectal terms commonly used for brown trout, included in their names. By targeting Rö-lakes, there was a minimum of a 90% chance of finding an historically or currently present brown trout population, compared with 11% when lakes were randomly chosen. Lake names were shown to be strongly associated with details regarding the fish fauna as well as the habitat. This study is, to my knowledge, the first published attempt to employ lake-name evidence in investigating fish species distribution. The entire data supports the idea of long-term stable brown trout lake distribution under pre-industrial natural conditions. However, since the 1920’s, 27% of Rö-lake populations were found to have suffered permanent extinction (extinction rate >3 % per decade) mainly associated with fish introductions. Historical names, fishers’ knowledge and documentary evidence combined with limnological data proved powerful in revealing the past natural distribution, as well as initiating restoration of brown trout lakes in Northern Sweden.