1914] Sumner, et al.: Physical Conditions in San Francisco Bay 5 
task of accurately portraying the principal life conditions to which 
organisms in general are subjected in San Francisco Bay. This work 
is the necessary preliminary to any investigation of the more special 
problems relating to this or that fishery industry. Furthermore, our 
experience has already made it evident that no satisfactory study of 
these problems can be attempted without the expenditure of much 
time and of expert labor on the part of a number of persons through- 
out a period of several vears. Any investigation less thorough than 
this would necessarily be superficial, and would probably involve a 
waste of time and of money. 
The decline of the oyster industry, in particular, demands a thor- 
oughgoing investigation on the part of competent experts, who should 
be detailed for this duty alone. According to Statistical Bulletin 
no. 289 of the United States Bureau of Fisheries (‘‘Oyster Industry 
of the Pacifie Coast States, 1912’’), the yield of oysters in California 
(ehiefly San Francisco Bay) has fallen from 420,000 bushels, valued 
at $867,000, in 1899, to 68,037 bushels, valued at $280,344, in 1912. 
A great diversity of opinion is expressed by those chiefly interested 
as to the cause of this disastrous decline, but all agree that the matter 
ought to be seriously investigated. 
While the present report does not claim to make any direct con- 
tribution to a solution of this problem, we are of the opinion that the 
physical data which we offer herewith will have to be fully reckoned 
with by those who undertake the task. Indeed, any investigation 
which is not based upon an adequate knowledge of these data may 
be dismissed as futile. 
An account of the methods employed in the course of our hydro- 
eraphie observations will be deferred to the following chapter. Those 
which were followed in the dredging and the plankton work will, 
however, be recorded briefly forthwith. 
At the dredging stations of the regular series we made use of one 
or more of the following types of apparatus: 
(1) The beam trawl. This was either of the Tanner or the Agassiz 
type, and varied in beam length from 3 to 12 feet (0.9 to 3.7 meters). 
(2) A special improvement of the Tanner trawl, to which we have 
given the name of ‘‘sledge trawl’’ (plate 8). It was found that the 
narrow iron runners of an ordinary beam trawl sank so deeply into 
the soft bottom of certain regions of the bay that the net speedily 
filled with mud and was landed with great difficulty, if at all. Not 
infrequently the bag burst just before leaving the water, so that the 
