the water during the pelagic egg and young 

 stages of the cod and the later yield of the 

 year class has often been described from 

 different areas. In Danish waters, Blegvad 

 (1926) notes that higher temperatures during 

 the time when the eggs and larvae are pelagic 

 is associated with higher year class yields. 

 This is confirmed by Jensen (1952a). Similar 

 findings are reported by Hermann (1951, 

 1953) for West Greenland, and Frost (1938) 

 for Newfoundland. On the other hand, A. 

 Dannevig (1947) says that the successful 

 1938 year class in the Transition Area is 

 associated with cooler water temperatures 

 than usual, the rationale being that spawn- 

 ing was delayed and the larval period cor- 

 responded better with the height of the 

 zooplankton cycle. Poulsen (1931), however, 

 states that the higher the temperature in 

 Danish waters, the more larvae he found, and 

 concludes that this is a reflection of the 

 availability of plariktonic food. 



A close association between the tem- 

 perature on Fylla Bank off West Greenland 

 and the later yield of the appropriate year 

 class has been reported (Hermann 1953; 

 Hachey, Hermann and Baily 1954). Here again 

 warmer years have produced better year 

 classes (fig. 1). 



Jensen (1929) found a similar rela- 

 tionship for Schultz* Ground in the Baltic, 



," 2" 3° 



BOTTOM TEMPERATURE IN JUNE 



--Relation between the temperature on ryi.a Dint nuX the field of i 



(Redrawn fron Hachey, Hermann ami Bailey 1954.1 



Teaperatures of recent years are narked by dotted I 



and Poulsen (1930) observed that the number 

 of larvae at Halskov Rev in the Belt and 

 Anholt Knob in the Kattegat increase as the 

 temperature increases when he compared 

 several years data, although he suspects 

 that the effect may be a secondary one, due 

 to the increased availability of plankton 

 as food for the larval fish in warmer years. 



Many laboratory experiments and direct 

 observations of the relations between eggs 

 and temperatures have been made. Fertiliza- 

 tion can take place as low as -2° (A. Dan- 

 nevig 1919) and probably at least up \o the 

 highest spawning temperatures recorde. , 12" 

 (McKenzie 1934b, Tremblay 1942). Observa- 

 tions have shown that eggs are fertilized 

 at 5.5° (Anonymous 1911) and as low as -1.7* 

 (Johansen and Krogh 1914), but eggs ferti- 

 lized at low extremes and kept at these 

 temperatures are unlikely to survive. Hen- 

 sen (1884) says that eggs die below -1.2°, 

 and Johansen and Krogh (1914) report little 

 or no development in eggs kept in tempera- 

 tures up to -1.2°, with only incomplete 

 development up to -0.3". They conclude that 

 the lower limit for full development lies 

 somewhere between -1° and 0°. These con- 

 clusions, however, are not entirely con- 

 sistent with the results of experiments 

 described below. 



The reports by Earll (1880) and H. 

 Dannevig (1895) seem to be the classics in 

 the study of time, temperature, and develop- 

 ment of cod eggs. (Table 1.) 



The results of the two experiments 

 agree very well with the exception of the 

 long periods at temperature below 0° . Even 

 this is not particularly disturbing when 

 it is considered that H. Dannevig's is an 

 extrapolated rather than observed figure 

 and that H. Dannevig himself comments on 

 the variable results obtained in this sort 

 of experiment. The temperatures given by 

 Br ice (1897) agree also, and those cited 

 by Hensen (1884) and Ryder (1886) differ 

 but little. 



Thompson (1943) is not specific about 

 temperatures for developing eggs, but he 

 infers that above 5 s is optimum, agreeing 

 with Brice (1897), who adds a top limit of 

 8.3". Johansen and Krogh (1914) have deduced 

 that cod eggs in the Baltic routinely devel- 

 op between 1° and 4° , and conclude inci- 

 dentally that Van't Hoff's theory that a 

 rise of lO* doubles the speed of chemical 



