58 SALMON AND TROUT PN ALASKA. 



months the surface temperatures var}^ between 55° and 60°, the 

 lower nearer the mouth. The surface densities depend almost wholly 

 upon the precipitation. During ordinar}^ weather the head of the 

 bay, from the pushing up of the dense bottom layers of water by the 

 tides, acquires about half the density of sea water; midway, on account 

 of the volume from the main stream from Yes Lake, the density is 

 reduced to about one-fourth that of sea water, increasing to one-third 

 or more as the mouth of the bay is approached. During freshets the 

 surface density is much reduced, the water becoming practically fresh 

 at times. The bottom temperatures vary from about 50° at the head 

 in 50 feet of water to 44° in 330 feet at the mouth, with corresponding 

 densities of about 1.018 — or nearly three-fourths the density of sea 

 water— to 1.0235, or closely approximating standard density. The 

 tows exhibit a very scant population of food forms in the upper bay, 

 "with a gradual increase as the mouth is approached and a sudden rise 

 upon entrance to the main channel outside. In the fresher waters 

 jellyfishes predominate; with increasing densitj^ and depth the crus- 

 taceans increase in number. 



This whole subject of the distribution of pelagic forms is of funda- 

 mental importance in the stud}^ of the sea habits of the salmon. With 

 the pelagic forms, of course, must be considered also the shore forms, 

 such, for instance, as the common amphipods (beach lice), which may 

 be found under stones at low water; perhaps, also, certain mollusks, 

 etc. The factors of temperature, density, light, depth of bottom, 

 proximity of shore, set and velocity of currents, influence of land 

 drainage, etc., require to be carefully studied. As yet nothing has 

 been attempted in Alaskan waters toward the solution of these 

 problems. 



It will be noted that the Karluk sockeyes taken in salt water in 

 June are of greater average size than those taken on subsequent dates 

 at the same place. Further, that the average size of the June spec- 

 imens is about t^^'ice that of the migrants from the Naha taken only 

 a few weeks earlier at Loring. If these Karluk sockeyes are 

 accounted yearlings of average size for the locality, which have left 

 the lake not earher than April, more likely in May, they either have 

 increased very rapidly in size since reaching salt water or were much 

 larger than Naha yearlings at the time of migration. But for the 

 uniformity of size it would seem more probable that the specimens 

 procured are the selected larger examples, the smaller escaping 

 through the meshes of the seine. There is the possibility that these 

 larger individuals were fry that reached salt water the previous sum- 

 mer, and that the absence of smaller specimens in the collections is 

 due merely to the escape of the fry and fingerling migrants of the 

 same season through the large meshes of the' seme. That year- 

 lings from Karluk Lake are larger than those of the same age from 

 the small lakes of Southeast Alaska may well be believed in view of. 



