— 8 — 



effects of hatching. The numbers of mackerel and whiting exhibit just the same 

 periodical changes which characterise the cod, and the maxima and minima of these 

 species are still more pronounced. And these fish have never been artificially propagated_ 



A glance at Fig. 2 also shows, that we find exactly similar variations in the 

 numbers of cod, mackerel and whiting, sold at the Christiania Fish Market from districts 

 outside Drobak. 



The statistics relating to flatfish inside Dr0bak deal only with so small quantities 

 for each year, that they are almost valueless. But considering the figures as they are, 

 a continued decrease cannot be made out. From an average of about 5000 Kilos in 

 the seventies the qantity marketed has declined. From 1890 to 1898 on the average 

 700 Kilo were sold. In the years 1899 — 1906 however the sale averaged 1300 Kilos. 



Whatever the reasons for these periodical and strangely coincident variations in the 

 quantities of different species may be, it is at all events sure, that these statistics 

 contain nothing to indicate that there are reasons for the variation in the numbers of 

 the cod, which do not exist in the case of the other species. 



As our knowledge of the fife and conditions of sea fish and especially our knowledge 

 of the cod gradually increased, doubts have arisen with regard to the theoretical basis 

 for the justification of sea-hatcheries. Thus in the year 1900 Dr. J. Hjort and the present 

 author published a book "Fishing Experiments in Noi'wegian Fiords" ^. 



In this book we set forth some general views on fishery questions, among others 

 on the artificial hatching of sea fish. 



Our views were founded on investigations carried out for a couple of years in the 

 Christiania Fjord, along the south coast and in the Trondhjem Fjord. With small 

 townets we fished for the pelagic eggs. We investigated the occurrence of littoral fry 

 with fine-meshed seines, and also endeavoured to study the main features of the current 

 system of these waters. 



As a result of these investigations we pointed out, that as regards the hatching 

 question the following facts were evidently of the greatest importance. The eggs and 

 larvae of most saltwater fish lloat in the upper water-layers and are conveyed by currents 

 from one place to another. We found that the currents in these fjords, which were 

 examined by us, carried great masses of eggs towards the ocean. In this fact we thought 

 we found the explanation of the peculiar fact, that the infant fry of fishes with pelagic 

 eggs was found in early summer to be very scarce in the fjords examined, while at the 

 coast and in the skiaergaard they proved to be abundant. In autumn considerable 

 quantities of littoral fry were to be caught in the same localities which during spring 

 had proved to be so poor. We explained this as an immigration, active or passive. 



These results, according to our opinion, threw new light on several old and 

 important fishery questions. As I have mentioned, the generally accepted theory of the 

 time was, that each little fjord had its own local tribe of fish which spent the whole of 

 its life there. Our results however seemed to us to show, that the fishes undoubtedly 

 must have a much wider area of distribution as long as the ova and larval stages were 

 bound to follow the movements of the water, movements which were known to imply 

 large areas in the fjords and along the coast. 



' Report on Norwegian Fishery and Marine Investigations. Vol. I. 1900. 



