283 
BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
unless the wind or currents were so strong as to carry it out of the 200-yard area. When 
the latter occurred, the ship was given enough headway to keep within the area. 
In order to supplement the information obtained from the plankton samples 
mentioned above, surface towings were taken with townets made of silk bolting 
cloth (No. 6 and No. 18 or 20) and a bottom towing with a similar No. 18 townet. 
The mouth of each surface net measured 30.5 cntimeters (1 foot) in diameter and that 
of the bottom net one-half meter in diameter. During the towing, which lasted 10 
minutes, the speed of the vessel was, as a rule, 2 knots. Samples obtained in this 
way were shipped to specialists for identification and in some cases for study from the 
point of view of distribution. The Copepoda, Medusae, and Sagittae were studied 
by Prof. C. B. Wilson, Dr. Henry B. Bigelow, and the author, respectively. Mr. 
Glassman and the author have undertaken a study of the distribution of the Mysidae. 
Most of the Crustaceae were sent to the United States National Museum, where they 
have been identified. 
A large beam trawl, whose runners were fitted with flat wooden shoes to prevent 
sinking in the mud, was used for the collection of fishes, sponges, ascidians, hydroids, 
bryozoans, and echinoderms. The duration of each trawling was 5 minutes; and the 
speed of the vessel was, as a rule, 3 knots. The fishes have been studied by Messrs. 
Hildebrand and Schroeder, the echinoderms by Dr. Hubert L. Clark, the ascidians by 
Dr. William G. Van Name, the bryozoans by Prof. Raymond C. Osburn, the hydroids 
by Prof. C. W. Hargitt, and the sponges by Prof. H. V. Wilson. 
Such animals as mollusks, annelids, holothurians, leeches, and many lower organ- 
isms which are found on the bottom or burrowing in the mud or sand, were captured 
either by the mud bag attached to the beam trawl or by the “orange-peel bucket.” 
The latter is a small commercial dredge that bites to a depth of about 0.5 meter, bring- 
ing up about 0.1 cubic meter of the bottom. The mollusks were sent for study to the 
National Museum, the annelids to Dr. A. L. Treadwell, the holothurians to Dr. 
Hubert Lyman Clark, and the leeches to Dr. J. P. Moore. 
SALINITY 
The determination of the salinity of a body of water is one of the necessary pro- 
cedures in a biological survey because the degree of salinity is believed to be a factor 
in determining the distribution of some of the animals and plants found in the water 
and because it is desirable to know how much the salinity varies from time to time. 
For this reason water samples were collected at each station visited, and their salinity 
determined by titration for chlorine, from which the salinity was calculated. 
The data on surface and bottom salinity and temperature will be discussed first, 
since many of the organisms collected and counted were taken at those levels. In 
this same part of the paper the vertical distribution of salinity and temperature will 
be taken up. After that, under the heading of seasonal distribution, data from inter- 
mediate waters will be compared at equivalent depths such as 20 and 30 meters. 
SURFACE SALINITY AT MOUTH AND HEAD 
The salinity of Chesapeake Bay, like that of other long bays and estuaries, grad- 
ually decreases, with very few exceptions, from the mouth to the head ; and the bay is 
known as a brackish body of water, although the failure, as a rule, of the fresh waters 
from the land and the saline waters of the sea to mix completely, and the variation in 
the volume of fresh and salt water entering the bay, result in different degrees of 
brackishness (Cowles, 1920). The surface data at the mouth of the bay show a vari- 
