2 THE IMPOVERISHMENT OF THE SEA. 



case, even great lluctuations in the annual produce of the latter fisheries 

 scarcely excite surprise, but a fairly constant yield is tacitly expected 

 of the bottom fisheries, when the same apparatus is employed, owing to 

 the oreater uniformity in the conditions of life on the sea-floor. 



It is probable, however, that the extent to which the stock of fish 

 on the sea-bottom depends upon variable elements, largely influenced 

 by the weather, is not fully appreciated even by the experienced 

 fisherman. The reproduction even of bottom fishes is profoundly 

 affected by the conditions of temperature, wind, and salinity pre- 

 vailing at the surface and inshore during the breeding season,* since 

 the majority of sea-fishes produce pelagic eggs, and many of them pass 

 their early youth inshore. Temperature affects both the duration of 

 the period of incubation and the rate of growth, directly by its action 

 upon the metabolism of the fish, and indirectly by its influence on 

 the growth and multiplication of lower organisms available as food. 

 Changes in salinity may kill the larvae, stunt their growth, or create an 

 impassable barrier to fishes on migration. Unfavourable winds during 

 the spawning seasons may drive millions of eggs and larvre to a 

 premature death. Even if the local weather, during any given term of 

 years, be admitted to have shown no marked abnormality, it is always 

 possible that weather changes of great magnitude beyond the region of 

 the fishing grounds may so divert the great ocean drifts from their 

 usual courses as to modify appreciably the normal distribution of 

 temperature and other factors within the region. The recent hydro- 

 graphic researches of Dickson, Pettersson, and others show that 

 considerable importance must be attached to this factor in any 

 determination of the physical influences at work in the North Sea 

 basin. It is all the more regrettable that there exists no permanent 

 organisation in this country which is adequately equipped for the 

 task of investigating the state of the sea from year to year, and 

 that such temperature data as are collected at coast stations and on 

 board ships are not summarised and published as regularly (if not 

 so frequently) as the observations made through the Meteorological 

 Office upon the state of the atmosphere. Water-temperature, salinity, 

 and the movements of great water-masses have relations to the fisheries 

 which are at least as intimate as the relations to agriculture of air- 

 temperature, rain, and the course of the air-currents. 



These considerations show the necessity of caution in comparing the 

 results of the fisheries in particular years, or for short terms of years ; 

 and considerable latitude must be allowed for temporary fluctuations 

 attributable to the effects of the weather, even if, with our present 



• Tlic tcnijicrature of tlic (leepcr water oirsliore immediately prior to tlic l)reediiig 

 season must also allect the mctaboli.sm of fishes, and probably, therefore, their fecundity. 



