82 



Fishery Bulletin 89(1), 1991 



50 100 50 100 50 100 50 100 

 Carapace length (mm) 



Figure 2 



Monthly size-frequency distribution of the commercial catch 

 (July 1985-February 1986) of Panulirus argus in Bahia de 

 la Ascensibn, obtained by converting tail weight (g) to carapace 

 length (mm). 



1981 



1982 



1983 



1985 



Figure 3 



CPUE (kg tails/boat day) of Panulirus argus for the fishing 

 seasons 1981-82 to 1985-86 in Bahia de la Ascensi6n (no data 

 available for January-March, 1986). 



Results 



Commercial catch and size composition 



The total catch of lobster tails in Bahia de la Ascen- 

 sion for 1985-86 was 42.5t, and for 1986-87, 63.0t. 

 The size composition of the commercial catch for July 

 1985-February 1986 is shown in Figure 2. Data for 

 March were insufficient and not included. There was 

 a mode around the minimum legal size throughout the 

 fishing season, except in July. 



The CPUE (catch/boat • day) data trends were similar 

 each year (Fig. 3). The highest CPUE occurred during 

 16 July-15 August, i.e., immediately after the open- 

 ing of the fishing season, followed by a sharp decline 

 over the next few months. This trend probably re- 

 flected both fishing and natural mortality, as well as 

 emigration. 



The values of F (fishing mortality), between 1.25 and 

 2.80, derived using a Leslie analysis (Leslie and Davis 

 1939) were highly influenced by the July data, which 

 were the annual peaks (Fig. 3), implying a different F 

 for that month. Therefore, the results of the analysis 

 were biased and could not be considered a good esti- 

 mate of mortality. 



Tagging results 



Of the total 3893 lobsters caught in 1985, 3470 were 

 large enough to be tagged (Fig. 4a). The male:female 



ratio of the captured population was 1.14:1, and that 

 of the tagged population was 1.13:1. Of the total 1403 

 lobsters caught during 1986, 1324 were tagged (Fig. 

 4b). The male:female ratios of both the captured and 

 tagged populations were 1.04:1. The size range of both 

 sexes was similar for both years. 



A total of 849 tagged lobsters were recaptured dur- 

 ing the 1985-86 fishing season (24.5% of total tagged 

 in 1985). None of the animals tagged in 1985 were 

 recaptured during the 1986 tagging period. However, 

 four lobsters tagged in 1985 were recaptured during 

 the 1986-87 fishing season. The male:female ratio of 

 recaptured animals was 1.14:1. Lobsters were recap- 

 tured in all sampling zones in the bay, as well as at some 

 localities outside of the bay. 



A total of 407 lobsters were recaptured during the 

 1986-87 fishing season (30.7% of total tagged in 1986); 

 the male:female ratio was 1.08:1. In this season, no 

 lobsters were recaptured outside the cooperative's 

 fishing grounds. 



In both fishing seasons, nearly all the recoveries 

 occurred during the first three months of the season 

 (e.g., Fig. 5). 



Population structure 



The mean CL (61.4mm, range 10. 2-142. 4mm) of lob- 

 sters caught in the Bay during 1985 was signifi- 

 cantly smaller (z test, Hoel 1976; z= 10.4, P<0.05) 

 than that of lobsters caught during 1986 (65.2 mm, 



