Náttúrufræðingurinn

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Náttúrufræðingurinn - 01.04.1949, Blaðsíða 46

Náttúrufræðingurinn - 01.04.1949, Blaðsíða 46
46 NATTURUFRÆBINGURINN hreinan stofn, fékk 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 frá 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 The 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. b. Countings of inerestic characteristics, especiaUy of vertebrae and kceled scales. It is concluded that these mclhods are inadequate wlien yoiing herrings are being delt with and may be misleading as regards older herring, especially during late siunmer, wlien it is difficult to distinguish maturíty stages III and VIII. Because of tlie shortcomings mentioned an attempt was madc to use the size of the herring when the first wintcr ring is formed, as a guide to race. Summer spawning herring should be of grcater size at this stage. Fig. I shows that the measurements have a two-peaked curve. However, the overlapping is so great that it is obvious that the method is not ápplicable for tliis purpóse. On thc other hand, very promising results emerged fiom a study of the otoliths. Characteristic diffcrences in the struture of the center are explained as due to different seasonal growth conditions during larval life. The otoliths showing an opaque ccnter are regarded as belonging to the spring spawning population, while the otoliths oí the summer spawning population have a hyaline, niore transparent area appearing as a depression in the center of the Otolith. This characteristic does not seem to alter during the life of the herring. Thus the opaque center corresponds to the summer zones formed during a period of a rapid growlh, while the hyaline center corresponds to the winterzones formed in autumn and winter when growth is slow. Thc figures show typical examples of this difference. By courtesy of Mr. Th. Rasmussen and Mr. Olav Aasen, 100 otoliths were received from a pure spring spawning population from Norwegian waters. The bulk of these otoliths are of the type figured in fig. 3. Some have, however, a very small hyaline ccntral 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 this characteristic.

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