79 



growth, feeding habits, and migrations, makes it evident that the 

 fishery-industry is also coming to appreciate it. 



It is no reflection on science that only certain of the links 

 in the life chain are yet known for any single fish in the sea, for 

 every case is one of great complexity. Each investigation also 

 involves the life histories of all the species of plants and of 

 animals, that may either serve the fish in question as food in one 



ary would xcau. j.iuiu one tvuiuiai-'ii lUQ^ivcxcx oi.j.0.-^ r. uw uxis^ jiiu^ j. j-vj uj.^ ^ .^ j. j. ._> -^ *v 



on which it feeds in part; the latter may feed on young mackerel; the 

 mackerel on larval herring, the latter on shrimps; these last on 

 copepods; the copepods on unicellular pelagic plants; while the 

 existence of the latter depends on the supply of nutrient salts in 

 solution in the sea water. Whatever reacts favorably or unfavorably 

 on the one, will react likewise on all the rest. The most important 

 problem for every individual fish, as for every man and woman on land 

 is that of food. Consequently, the welfare of the minute creatures in 

 the sea on which young fishes feed, finally harking back (via their 

 own food) to such elemental matters as the salts in the sea, and the 

 ajLount of sunlight falling on the surface of the water, is a matter of 

 practical importance to fishermen, and so, in turn, to the purse of 

 the consumer. 



The study of the life history of any marine fish involves the 

 physiological state of the parent as determining the viability of the 

 eggs and sperm; temperature ajid salinity as governing the hatch; the 

 character of the eggs whether buoyant or not; the duration of incuba- 

 tion, and the drift of the water as governing their dispersal; as 

 well as the supply of food (unicellular plants or minute animals) 

 available when the little fishes hatch (this last is probably the 

 most vulnerable stage, and the one most vital link in the life chain). 

 The toll taken of the larvae by enemies is also important. Probably 

 these headings include the factors that chiefly govern the relative 

 success of reproduction from year to year; hence knowledge of these 

 is essential for understanding the annual fluctuations of the stock, 

 and it is about precisely these matters that we still remain in the 

 deepest darkness. 



The direction and duration of the involuntary migrations of the 

 larvae, their food, their rate of growth, and the age at which they 

 either take to the bottom or begin to direct their own journeys, is 

 one factor; wanderings of the older fish the other, that governs the 

 interchange of fish between different banks, and the degree to which 

 certain grounds serve as nurseries for others. This with the impor- 

 tance of temperature as a vital factor, makes the study of the ocean 

 currents perhaps the most important single item in fisheries research 

 Knowledge of such matters as the food and spawning habits, the rate c 

 growth, the dominance of particular year classes, the enemies, the 

 general distribution, and the optimum temperature and salinity for th 

 older fish, are equally essential for intelligent management of the 

 fishery. 



There is nothing fanciful or extreme in the foregoing: the whol 

 field must be covered if effective remedies are to be found for even 



