Íslenskar landbúnaðarrannsóknir - 01.09.1978, Page 130

128 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
Fig. 1. Percentage distribution of the catches of brown trout in Laxá by length groups.
show the same sharp decline as seen for
the total catches, while there is an upsw-
ing in the upper section for the year 1976,
probably because there was a good year
class which now is being recruited. But the
net conclusion can be only that fishing at
the present time is too intensive, especially
in the lower section. Not only is the catch
per unit of effort declining, but the older
age groups are disappearing. Some re-
striction is therefore indicated.
BROWN TROUT IN VEIDIVÖTN
The Veidivötn are lakes situated in a vol-
canic area of south-central Iceland, 570 m
above sea level. They form a row of water-
filled explosion craters surrounded by vol-
canic ash. Few of the lakes have any outlet
or inlet. The bottom of those that do are
filled with volcanic ash or sand, with little
or no gravel, and the spawning conditions
are very poor. Only one lake, Stóra
Fossvatn, has adequate spawning areas.
Growth expressed by back-calculated
lengths is listed in Table 3 a and b for nine
lakes in the Veidivötn area, and for com-
parison the back-calculated lengths for six
other lakes are listed. In general the trout
keep on growing for a long series of years.
The largest and oldest fish was caught in
Snjóölduvatn. It measured 81 cm and
weighed approximately 5 kg and was de-
termined to be 14 years old. The lakes in
this area display a better growth than seen
in the other six lakes, with the exception
og Apavatn, where growth is faster than
anywhere else.