V) 

 Q 



I 60 



o 

 a. 



u. 

 o 



to 

 o 



Ui 

 (T 



o 



z 



5 40 

 o 



■I" 



■!■ 



HIGH TAKE BEFORE 1938 



MEAN TAKE BEFORE 1938 



!:°^1AKE BEFORE 1938 



i"i''±«^i«_^_„U 



36 



30 m 

 a. 



a: 



111 



24 a! 



in 

 u 



18 



30 40 50 60 68 70 



NUMBER OF DIVING BOAT UNITS 



Figure 21. —Levels of take per unit of effort. 



divided by 1,800 - the number of acres cov- 

 ered by one diving boat in 1 year) or 31 mature 

 sponges per acre (at a rate of 11 sponges per 

 pound). 



The difficulty in attempting to project the 

 return per unit of effort, as represented by 

 line A in figure 21, to a level of 20 boats or 

 less is in trying to determine the point below 

 which changes in the size of the sponging fleet 

 will not affect return per unit of effort. Theo- 

 retically any decrease in the number of boats 

 in the sponging fleet should result in a slight 

 increase in the average return per unit of 

 effort if they all work the same areas. Since 

 the boats move in a random pattern while work- 

 ing the sponge bars in any given area, some 

 bars will be worked more than once per year, 

 others only once, and some not at all. 



Before 1938 about 68 diving boat equivalents 

 were working the entire productive sponging 

 grounds. At the present time only one-third of 



the former area is producing sponges. In order 

 to have the same intensity of fishing on the 

 present area only 23 boat equivalents would 

 be required. With the present sponging fleet 

 of just under 17 boat equivalents the intensity 

 of fishing effort is below that of 1938 and about 

 equal to that of a 51-boat fleet working the 

 entire former sponging area. 



In region B, figure 21, the individual dots 

 indicate yearly returns per diving boat equiva- 

 lent; the circle, the average value; and the 

 line, the mean value over the 6-year period, 

 1951-56. This average take is much below the 

 very lowest return (line C) for the period 

 before 1938 and even below that of the average 

 take during 1940-47 when overfishing was 

 taking place. The best return per unit of effort, 

 however, was considerably higher than indi- 

 cated by the circle at B. The diving boat making 

 the best return in 1956 landed almost 2,200 

 pounds of sponges. 



63 



