are periodically covered with sand. This sand 

 tends to kill off many of the attached animals 

 and plants. The edge of the bar is a particu- 

 larly favorable zone for the setting of wool 

 sponges and is the area the spongers work 

 most intensively. Toward the central portion 

 of the bars or where individual sharp- sided 

 rocks are to be found, the surface of the rock 

 is covered with a heavy population of sponges 

 and other types of attached animal and plant 

 life. 



Sponging Bars in Relation to 

 Surrounding Bottom 



Contrary to the ordinary concept of sub- 

 marine rocky outcroppings, many sponging 

 bars are not above the general level of the 

 surrounding bottom but actually anywhere from 

 a few inches to as much as 6 feet lower. This 

 phenomenon is of considerable assistance to the 

 sponge fishermen. In deeper or slightly murky 

 water where it is impossible to locate a bar 

 visually, sounding leads are used. In most 

 cases the sand sample brought up by the soaped- 

 end of the lead gives the necessary informa- 

 tion about the closeness of a rock outcropping. 

 In many cases, however, a sudden deepening 

 of the water is indicative of the presence of a 

 bar in the immediate area; and if two sounding 

 leads are being used, a deeper sounding on 

 one side is sufficient indication to tell on which 

 side of the boat the bar is to be found. 



A series of echo sounding recordings was 

 obtained in the upper Gulf. These recordings 

 show graphically and in condensed form the 

 bottom contours near the sponge or fish bars. 



Figure 13 shows five selected sonic record- 

 ings of the bottom contour. Figure 13a is the 

 tracing of echoes off a fairly flat bottom, taken 

 while we moved from the shore towards deeper 

 water. The grassy bottom with the soft under- 

 lying fine sediment material gave an echo that 

 caused a wide recording on the tracing. In the 

 center portion of the recording, the echo trace 

 is narrow, thus indicating hard bottom. This 

 rocky bar was unusually flat, and very little 

 plant or animal life of any kind was to be found 

 on this bar area. 



In the second tracing three bar areas are 

 shown (fig. 13b). On the extreme left is a 

 tracing of high rock. 



The next three tracings of bars in deeper 

 water show the effect of the softer sediments 

 found at these depths in the area southeast of 

 Piney Point. A much thicker line is made by 

 the echoes off these softer sediments covered 

 with marine vegetation. In the central portion 

 of the third tracing, a very rough rocky bar 

 is indicated by the jagged thinner tracing fig. 

 13c. On the fourth tracing a rough rocky bar 

 is recorded (fig. 13d). The last recording 

 shows most clearly the edges of the bar in 

 the central portion of the tracing. These bars 

 were 4 to 5 feet below the general level of the 

 bottom. 



I consulted a number of oceanographers, who 

 agreed with me that the bars lying below the 

 general level of the bottom remain free of silt 

 only because of wave action. Over open bottom 

 the heavy growth of eelgrass and other marine 

 plants and the flatness of the bottom offer very 

 little resistance to the movement of the water 

 so that little turbulence is developed. During 

 diving I observed that the water among the bases 

 of the plants moved little if at all with the 

 motion of the waves. Over the rocky bars, 

 however, the many larger growths of coral, 

 sponges, and other bottom animals, as well as 

 the irregularities of the bar itself, create 

 considerable turbulence during the passage of 

 the waves. 



Examination of many bars leads to the con- 

 clusion that during long periods of calm weather 

 the bars are gradually encroached upon by the 

 finer sediments normally held in place by the 

 mat roots and rhizomes of marine vegetation. 

 Eelgrass is known for its role as a sediment 

 trap. During heavy wave activity from storms 

 or the passage of hurricanes through the Gulf 

 as observed in October 1956, turbulence over 

 the bar areas results in the uprooting of 

 quantities of marine plants and the shifting of 

 large amounts of sediment, as a result, some 

 parts of the bar areas are uncovered while 

 others are laden with sediment. 



Sediment Distribution Across the 

 Bar 



The bar areas support not only sponges, but 

 also populations of animals and plants that 

 form calcareous shells or skeletons. Most 



33 



