76 



continuing study (by all available methods) of ocean currents as 

 carriers of eggs and larvae; and of the length of time during which 

 these latter drift at the mercy of the current; information which, 

 again, can only be gained at sea. 



At first sight it might seem that the question "how" best to 

 vest the crop'would be purely economic, not biologic. Actually, 

 _ ^ ^,. _ ^_, ^^„„^„„ Thus, different 



epth- 



se 

 xo ine sux'iace, axiu m amuu i^n v»ca oihtj. , the pound— ne u or weir oi^-Ly 

 close to the shore-line, and only during the warm months if ice forms 

 during the winter; hook and line only where fish are feeding, etc. 

 'Vhether the grounds, depths or seasons, so determined by the method 

 adopted, are wise from the standpoint qf conservation, or the reverse, 

 can be settled only by knowledge of the life history of the particular 

 fish. 



For these same reasons, statistics of the amount of fish caught _ 

 may give a wholly erroneous picture of the abundance of the species 

 in the sea. ^hen the purse seiners report "no mackerel", for example, 

 it may merely mean that the fish are keeping down deeper in the water; 

 when otter-trawlers report "few cod" the latter may simply have con- 

 centrated on the rougher bottom where the trawlers do not fish. 

 Similarly, the reported landings, as classified by localities, _may 

 give e false im.pression of the regional abundance of the fish in the 

 sea, unless the actual locality of the capture is stated, which it 

 has seldom been possible to do except in a very loose way. 



"How to fish" has another biological aspect that cannot be 

 neglected: namely the effect that the fishery may have on enemy- 

 species that are caught incidentally, or on species upon which the 

 commercial fishes prey. Any method that will take and destroy large 

 numbers of destructive species may actually benefit the primary object 

 of the fishery, in spite of the draft that fishing makes on the 

 latter. In North American waters this applies especially to the 

 destruction of the Tog fish, of Skates, and of the Goose, - or Monk 

 fish. But off other coasts, where the last two are used for food, 

 the relationship is different. To destroy annually several hundred 

 million Menhaden, as is done to supply the demand for fisn oil and 

 for fertilizer, may seriously lessen the food supply for the Blue 

 fish, and so react against the latter. But the lives of so many 

 Menhaden are saved whenever a Blue fish ie caught that the death of 

 the latter may be economic gain. The interrelationships of aifferent- 

 species, as food or enemies, is thus a vital factor in the situatiocr 

 to disentangle this skein falls directly within the province of the 

 oceanic biologist. 



Ever since man first cast line into the sea> "can we broaden ov\ 

 fishing grounds?" has been a live question. With the passage of the 

 years one new fishing bank has been developed after another, and no 

 one can dispute thst the discovery of new grounds and of new bodier 

 of fish from which no toll has previously been taken, is so much pure 

 grain. Every fisheries bureau is therefore interested in testing the 

 possibilities of unfished parts of the sea by actual fishing 



