Náttúrufræðingurinn - 1952, Side 28

74
NÁTTÚRUFRÆÐINGURINN
sýna, að við höfum möguleika til þess að geta sagt fyrir um allar
meiriháttar sveiflur í stœrð stofnsins.
Takmark fiskirannsókna almennt er að kynnast sem bezt lífi fisks-
ins og því umhverfi, sem áhrif hefur á lífshætti hans. Þessi fróðleik-
ur verður svo fyrr eða síðar útgerðinni að gagni.
Sá árangur, sem hér hefur verið gerður að umtalsefni, er ótvírætt
spor í rétta átt, og má þakka það hinum miklu og samhangandi gögn-
um, er við höfum yfir að ráða. Ég vil þó taka fram, að hér er ekki
um neinar endanlegar niðurstöður að ræða. Fiskurinn er á ferð og
flugi og sífelldum breytingum undirorpinn. Okkur er því nauðsyn-
legt að vera vel á verði og gefa gaum hinum minnstu breytingum,
er raska þeirri mynd, sem við höfum á þessu augnabliki. Slíkt verður
ekki gert nema með áframhaldandi rannsóknum, og þær mega ekki
stöðvast, þráðurinn má aldrei slitna.
ABSTRACT
In this paper the author deals with a few results of recent investigations on the Ice-
landic stock of Cod.
During this century there has been a remarkable development of the Icelandic fish-
ing fleet. In 1913 it consisted of 13 motorboats liiggcr than 12 tons with a total tonnage
of 429, and 18 trawlers totalling 4257 tons. In 1950 there were 480 nrotorboats with a
total tonnage of 23.576 and 52 trawlers of 29.043 tons. Foreign fishing also has in-
creased greatly, f. inst. English trawlers made 1400 voyages to Icelandic fishing grounds
in 1907 but 3049 in 1931.
As shown in fig. 1 there have been two distinct maxima in the catch of cod since
1906, viz. 1930 and 1944. The one of 1930 is caused by the unusually strong yearclass of
1922 and the rise from 1938—44 is the yield of the yearclasses 1931—36. The output of
the different yearclasses 1920—36 at the age of 8—13 years is shown on fig. 4. The year-
class of 1922 has given abt. 705 thous. tons or 26% of these 17 yearclasses.
Data on the catch per-unit-of-effort are available since 1900, and some of these indi-
cate periodical variations, which mainly seem to be caused by the different strength of
the various yearclasses.
Fig. 3. shows the age-distributions of the spawning stock during the years 1928—50.
The most striking feature of the figure is the great fluctuations of the different year-
classes. The two yearclasses 1922 and 1924 together supplied aljout 72% of the total
Icelandic catch of cod during the period 1930 to 1937.
The material since 1928 has been examined with rcgard to the socalled spawning
zones and these have greatly extended our knowledge of the mature part of the stock
and also made possible cjualitative and quantitative predictions of the spawning stock
one year in advance. Fig. 5 shows the age distribution of the spawning stock in 1951
and it reveals some important aspects of the stock. The age at first spawning varies
lietween 4 and 14 years. There are 13 Spawning classes (fish becoming mature in the
same calender year) and as a rule the number in each spawning class is reduced by