seems to take place when temperatures are 

 between 7° and 10". Thompson (1943) con- 

 cluded that the relatively fast growth and 

 maturity of the North Sea and Baltic cod 

 is due to the temperatures in these areas, 

 which are higher than in the Northwest 

 Atlantic, but this is not borne out in the 

 case of the closely related haddock. 



Growth is related to feeding and 

 metabolism in general. With regard to 

 feeding there may be two effects, the tem- 

 perature in relation to the food organisms, 

 as discussed by Hjort (1914), or tempera- 

 ture acting directly on the cod. Grenfell 

 (1910) states that cod will not feed in 

 water below 1.1°, and this is in fair agree- 

 ment with McKenzie's findings that below 

 this temperature they eat only sparingly. 

 McKenzie (1934a, 1934c, 1935) kept records 

 of the feeding of cod in tanks and con- 

 cluded that temperature has marked effects, 

 most feeding being done between 2.2° and 

 15.5°. In the high part of this range, a 

 drop in temperature caused an increase in 

 feeding, while in the lower part an advance 

 in temperature did the same. Cod of all 

 sizes fed rarely below 0" , but small cod 

 fed up to 20". In addition, the sizes of 

 the pieces of food accepted varied with 

 temperature changes by a factor as large as 

 four, larger bites being taken in warmer 

 water . 



At the lower extremes it seems likely 

 that the metabolic rate is affected. Mc- 

 Kenzie notes (1935) that at -0.6° the fish 

 swim very slowly and their respiratory rate 

 is much reduced. 



In further experiments published in 

 1938, McKenzie found that the fish actually 

 seemed to have difficulty in swallowing 

 when the temperature reached 1.1°, and that 

 below this the cod apparently could not 

 open their mouths to full gape. 



In the natural environment, however, 

 Lucas and Wimpenny (1953) found small cod 

 feeding below 2*, although the optimum feed- 

 ing temperature for small fish has been given 

 as between 12" and 18" (Anonymous 1835a). 



Schmidt (1929) speculated that the 

 number of vertebrae, which increases as the 

 water becomes cooler as mentioned above, 

 might be related to the amount of food 

 available rather than to the water tempera- 

 ture per se. 



We are indebted primarily to McKenzie 

 for our knowledge of the feeding habits of 

 cod with respect to temperature. Summariz- 

 ing his observations and bearing in mind 

 the necessarily intimate relation between 

 feeding and anabolism, we may conclude that 

 cod feed regularly from about 2° to 15°. 

 This is, of course, an oversimplification, 

 because of the strong evidence that differ- 

 ent sizes of cod have different optima 

 within the general range, smaller fish tend- 

 ing to feed at higher temperatures. 



But as McKenzie (1934c) points out, 

 this range should be kept in mind when con- 

 sidering results from hook and line fishing 

 as indications of abundance and distribu- 

 tion. 



DISTRIBUTION AND ABUNDANCE 

 OF MATURE FISH 



Temperature 



The effect of temperature on the 

 distribution and abundance of the mature 

 cod has long been a subject for study and 

 also a matter of no little controversy. 

 There have been those who would define 

 "cod water" exclusively, Rodriguez M. and 

 Rojo L. (1955), for instance, who say that 

 on the Grand Bank it is water with tem- 

 peratures from 2° to 4°, and Huntsman (1925) 

 who cites 4.4° to 7.2°. But some authors 

 (Anonymous 1935b, McKay 1934) have denied 

 the existence of such an absolute entity. 



Of particular interest is the West 

 Greenland area, where cod were abundance 

 from 1810 to 1823, then scarce until re- 

 cent years when they have reappeared in 

 enormous numbers. In the Disko Bay area, 

 for example, cod were rare in the 1920's, 

 but lately 30 percent of the total catch 

 has been taken on the banks nearby. Taning 

 (1949, 1953) believes these changes are 

 associated with warming of the waters in 

 the early 19th century and again recently. 



Lundbeck (1954) describes a change 

 in distribution of cod in the Barents Sea 

 which correlates with an increase in depth 

 of the 0° layer. His rationale is that 

 bottom areas which were formerly too cold 

 have become habitable through this change. 



Hjort seems to have been too re- 

 strictive when he wrote (1914) that the 



