14 



latter, thus taking the character of stationary fjord fish, another 

 and larger part move further and further out on the ocean hanks 

 and the large edge towards the deep of the arctic sea, whence they 

 then return ripe for propagation. At this period they deliver their 

 tribute to the Lofoten fisheries, but the greater part of those that 

 escape the fishing tackle, return, after having spawned, to their 

 oceanic life. After the Lofoten fisheries there is usually the 

 "skraapfiske", which is most successful in Vesteraalen, for instance 

 at Gaukvsero. This seems to indicate that the fish-masses on returning 

 from Lofoten move northward. Even late in the summer some 

 stray specimens of the Lofoten cod may be caught, and these have 

 as a rule an emaciated appearance. 



The principal features of the life of the cod, as stated above, 

 may be modified in different ways. Mr. Saes gives instances of 

 this in his report for 1870. In the month of June the sand eel 

 (ammodytes tobianus) draw near the shores in order to spawn. 

 Consequently masses of cod, small and large, pursue it. By opening 

 the stomachs of cods taken. Sabs found that the contents almost 

 exclusively consisted of ammodytes, especially at the beginning of 

 the migration of the latter fish. Afterwards, when young herrings 

 appeared in numbers in the same places, the sand eel was refused, 

 and cod, as well as green cod, were found crammed with young 

 herrings. 



On the basis of Mr. Sabs's investigations and materials, pro- 

 fessor CoLLETT*) has given the following measures for the young 

 of the ocean cod: 



V, month old, total length 7 — 8 mm. 



1 - - ,: „ 12 



2 - - „ „ 15-20 „ 



3 - - „ „ 30-40 „ 



4 - - „ „ 54-60 ,. 



5 " )i )i ' ^ n 



6-7 — - „ „ 120-1.30 „ 



8— 9 — - „ „ about 195 „ 



9—10 — - „ ,. „ 240 „ 



12 — - „ „ 400—500 „ 



In the summer following on their hatching the cod, at least 

 a great part of them, are supposed to move out upon the outer 

 banks, in order to return, at three years of age, ripe for 

 propagation. For ocean cod ripe for propagation, Collett (1. c), 

 puts the length at 660 — 700 mm., while of the fjord cod the smallest 

 individuals ripe for propagation have the length of 350 — 400 mm. 

 A few times I have undertaken measurements of young cod caught 

 close to the Biological Station. On August 26th, 1895, the aquarium 

 was supplied with a number of young cod whose length was found 

 to average about 80 mm. On September 15th they all died from 

 want of air as the conduit had been choked. In the mean time 

 they had been well fed on mytilus edulis, and the following sizes 

 were found: 104, 88, 87, 93, 85, 85, 98, 97 mm., average about 

 90 mm. In 20 days the growth was consequently about 10 mm. 

 For another and larger lot, the feeding of which had been less regular 

 on account of the greater number, the increase during the same 

 time averaged 6 mm. This observation from the aquarium, however. 



*) Professor Collett, Norges Fiske, p. 104—107. 



cannot of course be directly applied to the relations in free nature. 

 This fry that on August 26th had an average length of 80 mm. 

 were of course belonging to the progeny of the year, after the 

 normal spawning time. At the beginning of June of the following 

 year a few shoals of young cod were seen near the station building, 

 some of which were caught and had a length of 140 — 215 mm. 

 These could not belong to the hatch of the year, but at the same 

 time they were also rather too small to be in their second year. 

 Even supposing that the spawning had taken place in the month 

 of February, they were still too large to be of the fry of the year; 

 if however we suppose the spawning to have taken place in May, 

 this fry would have been one year old, and even under that sup- 

 position they differed rather much from the normal size that pro- 

 fessor Sabs has found for the one year old progeny of the ocean 

 cod in Lofoten. In another part of the coast, in the harbour of 

 Larvik, I undertook, Nov. 25th, 1896, some measurements of small 

 cods. The length was here 190—200 mm., which very well agrees 

 with the measures given by Sabs for the corresponding stages of 

 development from Lofoten. The stomach was crammed with am- 

 phipods (e. g. gammarus) and decapods (e. g. crangon vulgaris). 



The majority of the fry of fishes is obliged to live on plancton 

 organisms, and while some continue plancton eaters all their life 

 (e. g. herring, sprat, &c.), there are others that, after eating nothing 

 but plancton during the first part of their life, later on change to 

 a mixed food of plancton and necton. The green cod (gadus virens) 

 is no doubt such a one, probably the mackerel too. Further, 

 there are some that rather soon leave off feeding on plancton, the 

 place of this food being taken by the rich crustacean fauna of the 

 littoral region. This is the case of the cod, and Sabs has shown 

 that for the Lofoten cod the change is made when the young have 

 reached the length of 60 — 60 nmi. That the young green-cod 

 continue feeding almost exclusively on plancton until they are at 

 least one year old, seems to me evident from the observations I 

 have made; though more about this later on. This circumstance 

 also explains the difference existing between the fry of cod and that 

 of green-cod in the choice of their staying place. At the periods 

 during which sufficient food is found in the surface layers, the 

 green-cod fry stay at shallow places (m small bays and in har- 

 bours), while they move into deeper water in the typical winter 

 months, when the plancton is extremely scarce in the upper layers. 



As for the grown-up fish (cod, green-cod, &c.), I have in the 

 following tried to give a somewhat detailed description of their 

 feeding conditions. 



The food of the cod. 



The celebrated knower of fishes, ^Ir. Kboybb, writes about 

 the cod that it may, on account of its voracity, be regarded as 

 the enemy of nearly all sea animals that it can master. It is 

 however of considerable interest to see what turns up in its stomach 

 in different places and at different times. I have therefore examined 

 a great number of cod stomachs. The conditions under which the 

 cod feeds in our waters have of course been investigated before, 

 especially by the professors Collett and Sabs. In "Meddelelser 

 om Norges fiske i aarene 1875—78", p. 65, Collett writes: "The 

 animal forms that contribute the chief food for the larger individuals. 



