378 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



The work upon the temperature and salinity showed that the 

 waters in this district increased in salinity with depth. The increase 

 took place much more rapidly at about the level of the edge of the 

 continental shelf. The adult halibut spawns on these edges ap- 

 parently just within the layer of denser water, in depths of about 

 150 fathoms, and its young, hatching and drifting as transparent 

 larvae, are carried by the currents in this denser water until the time 

 metamorphosis approaches. At that time the young rise into the 

 lighter surface water and into the more rapid currents there. It is 

 still unknown just how far the young are carried. In the surface 

 water they presumably drift inshore as well as alongshore, because 

 shortly afterAvards the young are found in shallow water and indeed 

 along the beach. 



Nothing in this early life history indicates that the young fish 

 drift far enough to get out of the coastwise currents. The silk 

 nets took them in great numbers immediately outside of the 1,000- 

 fathom line and in but scattered numbers farther at sea. The direc- 

 tion of the currents and the distribution of the eggs and larvae were 

 such as to make us certain that the young from the grounds of the 

 Gulf of Alaska, however much they might contribute to banks fur- 

 ther westward, could not contribute to those to the southward along 

 the coasts of British Columbia and the State of Washington. 



The picture is not yet a precise one. It is known only in its gen- 

 eral features. The currents in deep water perhaps move much more 

 slowly than we at present believe, and even in the upper layer of 

 water it is entirely possible that the drift is such as to carry the 

 young inshore rather than any greater distances along the coast or 

 seaward. Tliese are points which must be cleared up by further 

 research. The work of the Commission has not yet been completed. 



Spread broadcast in the sea as the eggs of the halibut are, it is 

 understandable why such gTeat numbers of them are produced. 

 Although the halibut does not usually mature until about its twelfth 

 year, nevertheless when it does mature it produces a great number 

 of eggs. The eggs are large, but the fish is also large. A 12-year- 

 old female may produce 200,000 to 500,000 eggs, depending upon its 

 weight, a 20-year-old female may produce between 1,100,000 and 

 2,750,000, w^hile some the the larger and older fish have been known 

 to produce as many as 3,500,000. That number of eggs would seem 

 more than a female could carry, but careful studies have shown that 

 only small numbers are ripe at any one time. Before the last stage 

 of ripening the eggs measured were approximately half a millimeter 

 in diameter, but just before shedding became translucent and large 

 and when shed averaged 3.25 millimeters. 



