28 U. S. BUREAU OF FISHERIES 



be distinguished but were found to vary somewhat in the position 

 of their upper and lower boundaries as well as in the richness of the 

 distinct animal communities characterizing them. Temperature, 

 light, and pressure appear to be the most important physical limiting 

 factors. As all life in the lower levels ultimately depends for food upon 

 organisms that descend from the surface waters, collections from even 

 the deeper zones in such areas as the Gulf Stream and about the Gala- 

 pagos Islands, where an abundance of surface life exists, were exceed- 

 ingly rich. Conversely, in barren areas like the Sargasso Sea, where 

 the surface fauna is scanty, the intermediate levels are very sparsely 

 inhabited ; in fact, so scarce was the animal life that it was at times 

 impossible to determine faunal limits. Although poor in species, 

 the zone yielding the largest hauls was situated just below the depth 

 to which surface animals descend in the daytime. This hitherto un- 

 recognized zone, between 400 and 700 meters, is now named the 

 "transition zone," as it comprises the zone of transition from daylight 

 to darkness. It adjoins the lower part of the "silver zone," recently 

 used in classifying the vertical distribution of fishes lying within the 

 limits of 150 to 500 meters. Below 2,000 meters and above the bottom 

 community, there appears to be a region (recorded first by the 

 United States fisheries steamer Albatross) visited only by scattering 

 forms or falling dead bodies. Although this theory has at times been 

 attacked, the Arcturus collections substantiate in every respect the 

 observations of Mr. Agassiz for those particular regions traversed. 



Enormous schools of tuna observed between Mariato Point and 

 Cocos Island from May 11 to June 3 were apparently making their 

 annual migration. A brief report on them has been submitted to 

 the bureau. 



Progress has been made in working up the data collected during 

 the hydrographic and biological survey of Chesapeake Bay, and it is 

 anticipated that the final report will be completed within a compar- 

 atively short time. 



The study of the currents, temperatures, etc.. in Massachusetts 

 Bay has already been mentioned in the discussion of the investigations 

 of the early life of the cod, pollock, and haddock. A report on cer- 

 tain phases of this investigation was prepared and submitted by 

 Richard Parmenter, temporary assistant. 



The comprehensive investigation of the oceanography of the Gulf 

 of Maine, which has been conducted for a number of years by Dr. 

 H. B. Bigelow, of the Museum of Comparative Zoology, Harvard 

 University, is nearly completed. The section dealing with the fishes 

 has been published already, that dealing with the plankton is in the 

 hands of the printer, and the section dealing with the physical ocean- 

 ography is in an advanced stage of preparation. 



In cooperation with the Bureau of Lighthouses, water temperatures 

 have been taken at a number of selected stations along the Atlantic 

 coast. 



ECOLOGY OF FRESH-WATER LAKES 



During the summer of 1925 limnological observations were made 

 on some 50 lakes in northern Wisconsin by Dr. Chancey Juday of 

 the State Geological and Natural History Survey. Most of these 

 lakes are situated in Vilas County and range in area from 3 to 1,500 



