eggs each were placed in hatching chambers with a volume of about 100 ml 

 (Fig. 9.2). These were kept in the hatching chamber system for 7-12 

 days. Two or three days after the appearance of hatched larvae in a 

 chamber, the contents were removed and preserved in 4% formaldehyde for 

 later examination. The temperature in the chamber system was between 10 

 and 14 C, corresponding to the in situ temperature for that time of 

 year. The oxygen content of the water in the hatching chambers was 

 almost saturated. 



9.3 Results 



The echo sounding surveys did not indicate any decrease or disappear- 

 ance of pelagic fish within the oil spill area. Furthermore, chemical 

 analysis of herring organs and whole fish showed no indication of oil 

 contamination (Boehm, pers. comm.). 



The frequency of spawning grounds was lower in the contaminated 



area than in the reference area (20%, n =20 and 45%, n =100). (Fig. 9.3 



2 2 



and 9.4). A x test was carried out (x = 3.3, d.f. = 1) and the result 



was found to be significant at the 7% level. 



There was no significant difference in the number of malformed 

 larvae. Only two larvae with enlarged areas anterior to the yolk sac 

 were found in two samples from the polluted area (picture, Linden, 1976). 



The hatching results are presented in Table 9.1. These are divided 

 into two columns, representing two different counting methods. The 

 first column (observed hatching) gives the percentage of hatched larvae. 

 The second column (theoretical hatching) gives the percentage of hatched 

 larvae plus the percentage of eggs with live nearly hatched larvae. The 

 hatching of eggs from one reference station, Jutskar, was unsuccessful. 

 This was probably due to a severe fungal infection, the causes of which 

 are unknown. As can be seen in Table 9.1, the average hatching success 

 was lower in the oil polluted areas. The hatching success of eggs from 

 Tistelholmen, the most affected area, was extremely poor, about 20% 

 (theoretical hatching). 



195 



