Náttúrufræðingurinn - 1949, Blaðsíða 54

46
N ÁTTÚRUFRÆBIN GURINN
hreinan stofn, lékk ég sendar 100 kvarnir frá Norður-Noregi, en
norski stofninn er, eins og kunnugt er, ómengaður vorgotssíldar-
stofn. 96 sýndu örugglega þau einkenni, sem hér hafa verið talin
greina vorgotssíld l'rá sumargotssíld, 2 voru skemmdar, en á 2 getur
leikið vafi, til hvors stofns á að telja þær eftir kvörnunum. Frekari
rannsóknir verða nú gerðar á þessum einkennum.
SUMMARY
Tlie Herring Otolith as a Guide to Race
Reference is made to various drawbacks connected with the methods usually em-
ployed in distinguishing seasonal races of herring, i. e.
a. Determination of the degree of maturity of the sexual organs.
h. C.ountings of merestic characteristics, cspecially of vertelrrae and keeled scales.
It is concluded that thcsc methods are iuadequate wlien young herrings are heing
delt witli and may he misfeading as regards older herring, éspecially during late
sitmmer, when il is difficult to distinguish maturity stages III and VIII.
Becausc of the shortcomings mentioned an attempt was made lo use tlie si/e of thc
herring when the first vvinter ring is formed, as a guidc to racc. Summer spawning
herring should he of greater size at this stage. Fig. I shows that the measurements have
a two-pcaked curve. However, the overlapping is so great that it is ohvious that the
method is not applicahle for this purposc.
On the other hand, very promising rcsults emerged fioin a study of ihc otoliths.
Characteristic differences in the struture of the center are explained as due lo
different seasonal growtli conditions during larval life. The otoliths showing an opaque
center are regarded as belonging lo the spring spawning population, while tlie otoliths
of the summer spawning population have a hyaline, more transparent area appearing
as a depression in the center of the otolith. Tliis characteristic does not seem to alter
during the life of tlic heiring. Thus the opaque center corresponds lo the stimmer
zones formed duriiig a period of a rapid growtli, while the hyaline center corresponds
to the winterzones formed in autumn and winter when growtli is slow. I'lie figures
sliow typical examþles of tliis difference.
By courtesy of Mr. Th. Rasmussen and Mr. Olav Aasen, 100 otolilhs were received
from a pure spring spawning population from Norwegian waters. The hulk of tliese
ololiths are of thc typc figured in fig. 3. Some liave, however, a very small hyalinc
central area.
It is hoped that further investigations on the samples taken in February 1948 in
Hvalfjörður and on more samples from Norwegian waters will clarify the extent of
variation in tliis characteristic.