On the basis of a concentration of effort 

 equivalent to a fleet of 68 diving boats certain 

 conclusions may be reached. When the take per 

 unit of effort is below 2,400 pounds per year 

 (the 1940-47 average), it should be a clear 

 indication that overfishing is taking place and 

 harvesting is retarding the natural replacement 

 of sponges. The very slow increase in return 

 per unit of effort during the past 6 years sup- 

 ports this contention. 



Average return per unit per year of effort 

 during the years 1951-57 was about 1,500 

 pounds. This indicates a concentration of 

 sponges on the bottom of about 10 per acre in 

 the area worked. This concentration is far too 

 low to bring about any substantial increase in 

 the number of sponges within a short period of 

 time. Line C in figure 21 suggests that a mini- 

 mum of 24 sponges per acre on the sponging 

 area is close to the lowest concentration neces- 

 sary for rapid natural repopulation of the beds. 



As concentrations of sponges in the present 

 growing area increase, bringing more of the 

 area into economic production, and additional 

 sponging area is added, the fishing effort will 

 be spread more thinly over the sponging 

 grounds. This is based on the assumption and 

 expectation that the sponging fleet will not in- 

 crease in size because of the limited number of 

 available sponging boats and experienced 

 sponge fishermen. Less concentrated sponging 

 will allow the sponges to increase in size, and 

 the larval producing potential will rise con- 

 siderably. As a result, concentrations of 

 sponges on the bottom may be expected to in- 

 crease more and more rapidly. 



Probable Sponge Distribution in 5 

 and 10 Years from 1957 



By using what we now know about the re- 

 productive cycle of the sponge, the growth 

 rate, the rate of dispersion, and the current 

 pattern, it is possible to make an estimate of 

 the probable direction and rate of expansion of 

 the wool sponging grounds during the next 5 

 and 10 years. Several features of the expected 

 future distribution are of considerable interest. 



Because of the slowness of the eddy circula- 

 tion, seaward extension of the sponging grounds 



all along the western coast from Tarpon 

 Springs to Steinhatchee will be slow indeed. 

 Most, if not all, of the spread into deeper 

 water will have to be by way of an extension 

 of the sponge producing area into the deeper 

 water from the northern eddy, south of Car- 

 rabelle. 



The most interesting evidence of extension 

 of the sponging area by this northern eddy was 

 gathered on the July 1957 exploratory trip. 

 Five half-hour dives were made at approxi- 

 mately 3-1/2 mile intervals in 50 feet of water 

 directly south of the mouth of the St. Marks 

 River, Stations XXIII and XXIV a, b, c, and 

 d (see fig. 10). The wool sponges collected or 

 seen were as follows: 



Station XXIII - None 



Station XXIV a - Only 2 wool sponges less 



than 2" in diameter. 

 Station XXIV b - 11 wool sponges under 



5", 3 over 5". 

 Station XXIV c - 8 wool sponges under 5", 



7 over 5". 

 Station XXIV d - 4 wool sponges under 5", 



5 over 5". 



No wool sponges were found west of these 

 stations; and although the evidence is limited, 

 the steady change in the ratio of small sponges 

 to large sponges is indicative of wool sponge 

 dispersion to the west of this area. 



Once the wool sponges are dispersed as far 

 west as Carrabelle, the meandering southward 

 current running counter to the shore current 

 will be primarily responsible for extension into 

 the deep-water zones. 



The only possible exception to the above pat- 

 tern may be the seaward circulation of water 

 in the area of the sandy zone off the Suwannee 

 River. A boatload of 12- to 14-inch wool sponges 

 was taken in the fall of 1956 on the southern 

 side of this sand area in 55 feet of water. This 

 would indicate that a small area in this region 

 was unaffected by the disease in 1947 and may 

 have been effective in spreading the wool 

 sponges seaward since that time. It was im- 

 possible to explore this area completely as 

 the area beyond the 60-foot depth was re- 

 stricted by the U.S. Air Force as a target range. 



64 



