178 KEPORT OF COMMISSIONER OF FISH AND FISHERIES. 



of lierrings, aud that, therefore, after the breeze lias gone down there 

 will be good fishing in those waters. 



2G. Among the hydrological causes the temperature of the icafcr doubt- 

 less, next to the ciuTents of the sea, exercises the greatest influence on 

 the herrings. V There is good reason to suppose that the herrings prefer 

 a certain even temperature of the water, and thst they consequently 

 avoid too warm or too cold water. This degree of temperature, however, 

 differs greatly according to the different locations, fisheries, and races of 

 herrings. The fishing for spawning herrings is, for example, on the east 

 coast of Scotland going on at a season of the year when the temperatm-e 

 of the water is very high (from the middle of July till the middle of Sep- 

 tember), or very low (January to March). The observations of the Scotch 

 and Dutch Meteorological Societies made during the Scotch and Dutch 

 summer herring-fisheries have sliown that the temperature of the water 

 most favorable to these fisheries is about 13'^ C. (55.4<^ F.). During the 

 Scotch winter-fisheries, however, the temperature of the water ranges 

 from 4*^.5 to 5^.5 0. (40.1° to 41.9° F.), ancj during the Norwegian spring 

 herring-fisheries it only ranged from 3° to 4^ C. (37.4° to 30.2° F.). But 

 our observations are still so incomplete and relate so exclusively to tlie 

 spawning-herrings, that it is impossible to say anything with absolute 

 certainty excepting the fact that the herrings, when the temperature of 

 the surface waters is either too high or too low, go to deeper waters. I 

 But as the changes in the temperature of the water are chiefly caused 

 by the much better known and more fully-observed temperature of the 

 aiir and by the currents of the sea, we refer the reader to what has been 

 said above (13 and 22) regarding their influence on the herrings. It will 

 be clear that the former has a more decided influence during summer and 

 the latter during winter. 



As has been mentioned above (18), the agitation produced in the 

 water by strong wind is favorable to fishing, by mixing the upper and 

 lower layers of the water and by thus equahzing its temperature. 



The ]>reference shown by the herrings for an even temjierature of the 

 water, has led to attempts to explain thereby the apparent irregularity 

 in the occurrence of the herrings. 



27. It is well known, from olden times, that the formation of ice on the 

 sea has an influence on the herrings and the herring-fisheries, although 

 we do not possess suflicient observations on this point to form any cer- 

 tain scientific opinion. From Professor EdltincVs observations regarding 

 the formation of ice in the sea, we know that the formation of bottom- 

 ice will drive the herrings away. It is more than a mere supposition 

 that the formation of bottom-ice not only drives the herrings away but 

 also destroys their eggs and young ones, and on those coasts — for in- 

 stance, of the Baltic — where ice is frequent in winter, the herrings do 

 not spawn during that season. It is likewise well known that on the 

 coast of Canada much floating ice keeps the herrings and other fish away 

 from the coast. On the coast of Bohusliin, however, it has been observed 



