CHAPTER 9: IMPACT OF OIL ON LOCAL FISH FAUNA 



(Sture Nellbring, Sture Hansson, Gunnar Aneer and Lars Westin) 



9.1 Introduction 



From earlier echo sounding surveys (Aneer et al., 1978) it is known 

 that pelagic fish (herring, Clupea harengus membras , L. and sprat, 

 Sprattus sprattus L.) are very abundant in the spill area during late 

 autumn and winter. It is also known that herring spawn in the archi- 

 pelago in the spring. In view of the not inconsiderable local com- 

 mercial fishery, the following questions were of interest after the 

 spill: Were the pelagic fish still present in the area and were the 

 fish contaminated by the oil? Did the oil affect the spawning grounds 

 and the hatching results (c.f. Linden, 1976)? 



9.2 Material and methods 



To investigate the occurrence of pelagic fish in the polluted area, 

 echo sounding surveys were carried out on four occasions (11 November 1977, 

 15 December 1977, 11 January 1978, and 12 April 1978). The survey 

 routes are illustrated in Fig. 9.1. 



Herring were caught with gill-nets or by trawling. Organs (gills, 

 stomachs) and whole fish from the reference and affected areas were 

 deep-frozen for oil analysis. 



In order to investigate spawning grounds, 100 randomly chosen 

 non-polluted stations and 20 polluted stations were visited in June 1978 

 (about seven months after the spill) by SCUBA divers to see if any 

 spawning had taken place. At each station, the divers investigated the 

 bottom from the shoreline down to a depth of about 10 m. 



At stations in the affected area where spawning had taken place and 

 at four non-polluted reference stations, egg samples were taken for 

 hatching in the laboratory. At each station two samples were taken by 

 cutting and removing sections of algae with attached roe. In the labor- 

 atory the two samples were mixed and ten sub-samples of about 50-100 



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