52 



OYSTEB BOTTOMS IN MATAGORDA BAY. 



shown in the following table, the height being recorded in feet above 

 or below the plane of reference: 



Date. 



1905. 



January 



February 



March 



April 



Mav 



Average 



Average 



Lowest 



low tide. 



high tide. 



tide. 



Feet. 



Feet. 



Feet. 



0.00 



+0. 15 



-0.4 



+0.11 



+0.28 



-0.4 ! 



+0.64 



+0.78 



+0.2 1 



+0.92 



+1.15 



+0.4 



+1.43 



+1.65 



+1.0 | 



1 



tide. 



Feet. 

 +0.4 

 +0.7 

 + 1.4 

 +1.7 

 +2.1 



A curve showing the daily mean tide at the gage from January 

 20 to May 7, inclusive, is shown on plate x, facing page 00. 



Upon this question of the tides three important factors in oyster 

 production are dependent, namely, the production of currents, the 

 regulation of the density, and the exposure of the bottom. The first 

 two will be treated hereafter under their appropriate heads, but the 

 latter can properly be considered here. 



It is a matter of common knowledge that in many places, espe- 

 cially in the South, oysters are subject to daily exposure to the air, 

 and apparently suffer but little or not at all in consequence. When 

 the tide leaves them they close their shells, and retain within them 

 sufficient fluid to sustain the vital functions until they are again 

 covered, and this conservation of the necessary fluids can be sus- 

 tained for several weeks or, under some conditions, for months. 

 Eventually, however, in cases of prolonged exposure, the muscle 

 closing the shell must relax from sheer fatigue, the fluid escapes, and 

 the animal dies, as can be seen on examination of the shores and reef 

 crests of the bay. 



An inspection of the accompanying chart will show a fringe of 

 scattering oysters along practically the entire southeastern shore of 

 the bay above Tiger Island, and on the northwest shore above Stump 

 signal. During the summer months, when the tides are high, the 

 minute swimming fry derived from the spawning oysters in the 

 vicinity are carried by the currents into the shore waters, where they 

 settle down and attach to the shells and other firm bodies there found. 

 For some months after their attachment their environment remains 

 favorable and they flourish and grow, but with the advent of winter 

 the tides gradually drop away and they are left for longer and longer 

 periods exposed to the air and sun. Many of them have set in water 

 so shallow that they are left bare for a large part of December, 

 January, and February, when the tides are at their lowest; the 

 bottom on which they lie becomes seamed and cracked from the effects 

 of sun and wind, the oysters sicken, relax, and eventually die. 

 During March and April, when the scattering shore growths of the 

 upper bay were examined by the survey, a very large proportion of 

 the oysters were dead or dying ; few, if any, were of sufficient size for 



