In the commercial area there is an 

 obvious shifting of the population 

 structure toward the small size 

 individuals as commercial size lob- 

 sters are harvested. In the Nation- 

 al Monument, population structure 

 shifts toward the middle, the most 

 frequent size classes being those of 

 harvestable length. 



Direct evidence of residency 

 comes from the results of tagged 

 juveniles and adults. Of all the 

 lobsters tagged, released, and 

 returned, none were reported from 

 outside the Dry Tortugas area. By 

 comparison, lobsters released in 

 Biscayne Bay were found all through- 

 out the Keys. Preharvest standing 

 crop of P. arqus is estimated at 

 58.3 kg/ha. 



Subsequent to initial monitor- 

 ing, sport harvesting was allowed 

 for one season (8 months). During 

 the following season (16 months) 

 harvesting was again prohibited as 

 the spiny lobster population was 

 assessed for impacts. Immediately 

 following the harvest season, moni- 

 toring revealed a 58% reduction in 

 catch rate and only 42% of the 

 preharvest lair occupancy density. 

 The population in the control area 

 remained essentially unchanged. 

 After one year the catch rate re- 

 turned to 78% of its preharvest 

 value while lair occupancy density 

 returned to 71% of its original 

 level. Apparently a number of years 

 may be required for the population 

 to return to preharvest levels. 



Similar evidence of commercial 

 fishery impacts comes from Warner et 

 al. (1976). Before the season the 

 mean carapace length of lobsters 

 near Key West was 77.5 mm (3 in) and 

 modal length 74.5 mm (2.9 in). 

 After the fishing season opened mean 

 and modal length dropped to 72.9 and 

 68.5 mm (2.8 and 2.6 in) respective- 

 ly. Figure 61 summarizes the ef- 



fects of differing degrees of fish- 

 ing intensity on lobster population 

 distributions in the Florida Keys. 



z 



LU 



o 



LU 

 Q. 



Legal Limit 



▼ 



Lower Florida Keys 

 1975-76 

 n : 2,666 

 x:. 72.9mm 



40 

 30 

 20 



10 

 



Ft. Jefferson Dry Tortugas 

 1973 

 n = 812 

 x ;101 mm 



25 35 45 55 65 75 85 95 100 105 115 125 135 145 155 

 CARAPACE LENGTH Imml 



Figure 61. Length frequency dis- 

 tributions of Panulirus 

 arqus in three areas of 

 the Keys (adapted from 

 Warner et al. 1976). 



Davis (1977) suggests that the 

 present legal limit of 76.2 mm (3 

 in) allows the taking of many female 

 lobsters that have not yet reached 

 sexual maturity. This may suppress 

 the productivity of a resident popu- 

 lation in the Keys. The premature 

 cropping of local spawning potential 

 may also lend artifical support to 

 the Carribean import theory. Warner 

 et al. (1976) take this idea one 

 step further and suggest that such 

 removal may constitute a genetic 

 selection pressure favoring smaller 

 females that develop reproductive 

 capacity at a younger age. 



More recently, Lyons et al. 

 (1981) documented similar effects on 

 the lobster population in the upper 

 and middle Keys. Mean and modal 



208 



