Íslenskar landbúnaðarrannsóknir - 01.09.1978, Blaðsíða 132

130 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
TABLE 2.
Catch statistics for Laxá river 1974—1976.
Catch per rod
Number fishing - rods Catch per day
Fishing area 1974 1975 1976 1974 1975 1976
Geldingsey 3 295 o co 159 3.14 1.79 2.86
Arnarvatn 2 121 184 131 3.14 1.79 2.86
Geirastadir 2 309 228 118 3.36 2.59 2.07
Helluvad 3 263 398 326 2.17 2.87 3.20
Hofsstadir 3 439 359 367 2.78 2.43 2.87
Hofsstadaey 2 436 386 504 4.59 2.91 4.27
Brettingsst. 2 151 115 36 3.15 2.19 1.89
Hamar Upper section 2 113 116 131 2.46 2.39 2.70
combined 19 2,127 2,025 1,772 3.04 2.24 3.05
Ljótsst.-Audnir 2 72 126 39 1.80 2.00 1.22
Hólar-Árhólar 3 131 157 93 1.98 2.36 1.30
Audnir-Thverá 2 141 220 60 2.43 2.28 1.55
Árhv.-Kasthv. 2 222 129 114 4.04 1.56 1.70
Birningsstadir 3 286 197 100 3.14 1.57 1.29
Kasthv.-Presthv. Lower section 2 105 90 45 3.28 1.91 1.15
combined 14 957 919 451 2.80 1.91 1.39
trout and sticklebacks. A gillnet series of
seven nets with mesh sizes of 19.5—45.0
mm measured from knot to knot was used
in 1975 to collect samples ofchar. Length
and weight of each fish were taken,
otoliths were collected for aging, sex and
stage of maturation were recorded, and
stomachs were preserved for food
analysis. The stomach contents of fish
from certain length groups collected at
different times during the summer were
mixed and subsampled, expressed as total
volume percentages of each food item.
The length distribution of all char
caught in 1975 is depicted in Fig. 4. Table
5 contains the results of the age readings.
The oldest fish were 14 years old, but ag-
ing beyond that was difficult; some fish
might possibly have been older.
The char are fully recruited to the
gillnet sizes used at a length of 28 cm.
Each cm group usually contained 5 or 6
age groups. Since age readings were not it
proportion to the total number of fish
caught within each centimenter group the
age readings were multiplied by the in-
verse of the ratio between number of fish
aged and total number caught by the
gillnets for the respective length groups.
The total annual mortality could then be
determined from the age-frequency dis-
tribution, giving an estimate of 38% per
year.
The lake was lightly fished until 1975,
but since then it has been fished inten-
sively in order to improve the size and
quality ofthefish. Priorto 1975 theannual
catch was about 2000 fish. When traps