— 139 — .loii.s. SCHMIDT 



B. The species investigated, their spawning regions and the external conditions 



characterizing these 



I sliall liere give ii very brief description of the spawiiinj,' icffion of eaeh species dealt 

 with and ol' tiie limits witii rej^ard to depth, temperature and salinity within which spawn- 

 ing takes place. Lastly, the various species will be grouped together according to their 

 requirements during the spawning season with regard to tiie three outer factors mentioned. 



1. Polar cod {Gadus saïda Lep.) 

 This distinctly arctic species only spawns to a small extent within the regions invest- 

 igated by us and only in the coldest parts, namely the northern and eastern coasts of 

 Iceland. It is perhaps even restricted to the polar ice which appears on these coasts. Of 

 all the species this is the only one whose southern limit and not at the same time 

 the northern limit lies within the regions investigated. It does not belong in fact to the 

 Atlantic species, and its occurrence within these regions may be regarded as quite excep- 

 tional and depending upon the extremely abrupt changes in the hydrographical conditions 

 on the coasts of Iceland, perhaps also on the proximity of waters always filled with 

 polar ice. 



The spawning boundaries for this species are: 

 northern limit: north of the regions investigated; 

 southern limit: the cold parts of the Icelandic waters; 

 minimum temperature: ? 

 maximum temperature: at most ca. 2° — 3° ; 



principal spawning time: found spawning at N. Iceland in the beginning of 

 summer. 



2. Cod {Gadus callarias L.) 



Both the northern and southern boundaries lie within the regions investigated. Of 

 all our Atlantic gadoids the cod is the species which is able to spawn at the lowest temp- 

 erature and salinity \ and the range of variation in this respect, especially as regards the 

 salinity, is considerably greater than for |most of the other species. With regard to depth the 

 cod belongs to the species which can spawn in quite shallow water (less than 25 meters). 

 With exception of the cold parts of Iceland (cf. p. 121 — 22), the Bay of Biscay and partly 

 also the English Channel, cod fry are produced everywhere within the regions investigated, 

 in greatest quantities at S. and W. Iceland and the Faeroes, but also in quantities in the 

 North Sea and. on the Atlantic coasts of the British Isles, decreasing in quantity however 

 from north to south. (The cod also spawns in the Kattegat, Belt Sea and even in the Baltic). 

 The boundaries for the spawning are: 



northern limit: the warmer parts of the Icelandic waters; 



southern limit: the waters S. of Ireland and the Channel; 



minimum temperature: ca. 4° (3°— 4°, but little spawning under 4°); 



maximum temperature: ca. 9 — 9^2°; 



principal spawning time: spring. 



• Thus in the inner Danish waters and in the Baltic spawning takes place at a salinity of 20°/oo 

 or even far less. On the other hand it can also stand high salinities, as appears from our discovery of 

 cod eggs over the "new" bank W. of the Fferoe Bank (St. 62, 1905), where the salinity from the bottom 

 to the surface was 35-28— 35-29 »/oo. On the other hand no spawning seems to take place where the 

 salinity exceeds ca. 35-30 »/oo (Cf. St. 10, 11, 18, 1908j. 



18* 



