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Medientyp:
E-Artikel
Titel:
Exploitation and Conservation of the Thingvallavatn Catchment Area
Beteiligte:
Jónasson, Pétur M.
Erschienen:
Munksgaard International Publishers, Ltd., 1992
Erschienen in:Oikos
Sprache:
Englisch
ISSN:
0030-1299;
1600-0706
Entstehung:
Anmerkungen:
Beschreibung:
<p>Iceland was settled after AD 870. The fluctuations of the human population of the Thingvallavatn area are known since 1703. The catchment area is well suited and has been used for sheep farming for 1100 years. An increasing grazing pressure, especially during the last 200 years, is documented. The lake has been protected from large scale construction works until 1959. Commercial fishing began at the turn of the century and increased gradually. The fishing pressure, especially on large benthivorous and piscivorous arctic charr and brown trout, apparently peaked after the middle of the century. The fishing pressure on the planktivorous arctic charr for the local market increased moderately up to 1937, but then increased more rapidly due to the favourable prices offered by the canning industry to peak during the last half of this century. The planktivorous charr changed from being the cheapest fish on the local market to become a rare, expensive delicacy for the export market, which caused an 8-fold increase in fishery over a period of 100 years. The first material changes in the limnology of the lake occurred in 1959 after the establishment of the power plant at the outlet and damming of the lake The ecological effects of this construction are three-fold. First, from then on water-level fluctuations changed from a regular to an irregular pattern. Second, the dam prevented the brown trout population from spawning in the outlet river. The removal of a top predator in a ten thousand years old, well-balanced ecosystem was of profound influence. Now, thirty years later, the consequences are obvious: without access to its main spawning locality the brown trout gradually disappeared from the ecosystem. Third, almost the total population of the american black-fly Simulium vittatum Zett. disappeared from the outlet river Sog when the lake was dammed. Thus the Arctic charr populations lost their main food resource during early summer. Production of electric and geothermal power is at present and will remain the main economic use of the catchment area. Conservation has been going on since 1928. Approximately 25% of the catchment area is within the Thingvellir National Park, a part of which is fenced. The northernmost part of the catchment area has been protected from grazing since 1975.</p>