stopped by very heavy rains and overcast 

 from the afternoon of September 30 to the 

 late afternoon of October 2 (fig. 7, page 

 47). Unhampered, the organisms increased 

 in numbers and spread to new areas. The 

 airborne toxin was causing extreme discom- 

 fort along several miles of beach. When 

 the weather cleared two more planes were 

 summoned and all four planes sprayed on 

 October 2, 3, and 4 (see figs. 8 and 9, 

 pages 48 and 49). 



By October 5 spraying from the north 

 and south had restricted the heavy infesta- 

 tions in the area from Cleeirwater Beach to 

 the north end of Honeymoon Island (fig. 10, 

 page 50). Two planes finished dusting the 

 heavily infested patches in this area (figs. 

 11 and 12, pages 51 and 52). The last 

 inshore patch was sprayed on October 8 (fig. 

 13, page 53). Water samples were taken 

 daily and coordinated with aerial observa- 

 tions of the affected section to quickly 

 indicate any signs of recurrence. 



Following the major spraying water 

 samples were taken farther offshore and the 

 October 8 samples showed high concentrations 

 8 miles off Belleair Beach and 10 miles 

 northwest of Anclote Key. Another inshore 

 concentration just off Honeymoon Island was 

 treated on October 9 with a light copper 

 sulfate spraying. The offshore concentra- 

 tions are beyond the practical range of the 

 small crop-dusting planes. Any far offshore 

 control by dusting must depend either on 

 multi-engine planes or vessels. 



The areas of high infestation on var- 

 ious dates during this outbreak stretched 

 along 32 miles of beaches from Anclote Key 

 on the north, south to the Don Ce-Sar Fed- 

 eral Center at St. Petersburg Beach (fig. 2, 

 page 42). The total area sprayed was appro- 

 ximately 16 square miles, or 10,240 acres. 

 The attempted rate of spraying was 20 pounds 

 per acre, and 210,000 pounds of copper 

 sulfate was used which gives a close appro- 

 ximation of the desired aimount . 



The number of fish killed by the red 

 tide cannot be estimated accurately, but 

 it would certainly total in the millions. 

 Thus a kill of one fish per square yard 

 equals about 5,000 per acre or approximately 

 50,000,000 in the estimated 10,240 acres 

 of water dusted. At times the numbers of 

 freshly killed fish greatly exceeded this 

 density in fair sized patches. However, due 



to the drifting action of the wind and the 

 convergence of currents along tidal inter- 

 faces the dead fish soon tend to form in 

 long dense windrows, making jiny accurate 

 tallies impossible. Furthermore, the fish, 

 such as mackerel, without swim bladders 

 Sink when killed. The fish killed were 

 preponderately much below commercial size, 

 and chiefly of no n- commercial species. 



The costs to October 9 for copper 

 sulfate, spraying, plane charter and vari- 

 ous miscellaneous items were approximately: 



Gulf Fishery Investigations' 



Research Funds $13,000 



State of Florida Red Tide 

 Emergency Fund .... 



TOTAL COST 



30,000 

 $43,000 



Examination of figures 14 to 18 

 (pages 54 and 56) shows that although the 

 spraying promptly reduced the organisms to 

 practically nothing in the areas sprayed, 

 the effects were not lasting. In a matter 

 of two weeks concentrations in 2 out of 5 

 localities had again reached fish-killing 

 proportions. Since the range in density 

 of G. breve required to kill fish varies 

 with the species of fish from a minimum of 

 about 250,000 to 500,000 or more per liter, 

 we have arbitrarily shown 250,000 per liter 

 as the killing concentration in the figure. 



SUMMARY 



This large-scale attempt at control 

 showed that : 



1. For areas close to land (up to 

 about 3 miles offshore) and in shallow 

 water (up to at least 30 feet) spraying of 

 copper sulfate crystals at about 20 pounds 

 to the acre will destroy the red tide 

 organisms. 



2. There is a high probability that 

 the organisms may again become numerous in 

 such a dusted area. On the basis of this 

 one experiment it appears that they might 

 rebuild within 10 to 14 days. 



3. The cost of this dusting was 

 about $4 per acre. On the basis of experi- 

 ence gained we believe this cost can be 

 readily reduced to $3 per acre. On the 



