216 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. 



mately connected with each other, it must also be supposed that the 

 regular changes of time and i)lace are likewise connected. The later 

 arrival of the herrings in a more northerly place than usual would indi- 

 cate the near end of a fishing-period in one case as an earlier arrival in 

 a more southern place in the other. 



65. The tavorable conditions on which the development of a great race 

 of herrings depends are only found on a coast which is near the open 

 sea. The great race of herrings which has periodically visited the coast 

 of Bohuslan can scarcely be supposed to have developed there (at least 

 not under conditions like the present), and the greater distance from the 

 sea (and more especially from the Polar currents with their abundance 

 of "herring-food") is doubtless the chief cause why the Bohuslan fishery- 

 periods are more distinct, shorter, and separated by longer intervals than, 

 for example, the fishery-periods of Western iNl^orway. The same cause 

 might also explain the fact that the sea-herrings for a number of years 

 came sooner to the western coast of ISTorway than to the coast of Bohus- 

 lan, and that the space of time between the earliest and the latest arri- 

 val of the herrings near the coast was so much greater during the last 

 Bohuslan than during the last West ISTorway fishery-j^eriod. 



Another cause of the relative shortness of the Bohuslan fishery-peri- 

 ods may be found in the circumstance that, as the herrings belonging 

 to the coast of Bohuslan spawn in spring, this season is the most suit- 

 able for spawning on this coast, whilst in the Kattegat, the Sound, and 

 the Belts autumn is the more favorable season. As the sea-herrings 

 which visited the coast of Bohuslan during the great fishery-periods 

 chiefly spawned in autumn, it must be supposed that during their visit 

 to the Skagerack they were compelled to spawn under comparatively 

 unfavorable conditions, especially as regards the newly hatched young 

 ones. This may, to some extent, have induced them to seek other spawn- 

 ing-places sooner than would have been the case otherwise. It is also 

 quite likely that the coast of Bohuslan, towards the end of the fishery- 

 period, when the herrings did not come in till December, was less invit- 

 ing (at least for those herrings which spawned during winter). This may 

 also have been caused by unfavorable weather. If, as Axel Boeck has 

 shown, a temperature of the water of + 3° 0. (37.4° F.) is not injurious to 

 the herrings, it does not follow that this is not the case with a lower tem- 

 perature accompanied by the formation of bottom ice. As most of the 

 spawning-i)laces on the coast of Bohuslan are located in shallow water, 

 the cold must produce far greater changes in the temperature of the 

 water than in the spawning-places on the western coast of ll^orway, which 

 are located in deeper waters and are exposed to a much more powerful 

 current of the sea with a far more even temperature. Too little atten- 

 tion seems to have been paid to the great injuries which several closely 

 following severe winters must have inflicted on the spawning-places of 

 the herrings. This unsuitableness of the coast of Bohuslan as a spawn- 



