Lozano-Alvarez et al.: Fishery, growth, and movements of Panulirus argus 



87 



of 689 females were found with re- 

 mains of empty egg capsules and/or 

 eroded spermatophores. In both 

 years, all of the females that showed 

 signs of reproductive activity were 

 caught on the edge of the reef 

 (zones II and V, Fig. lb). No other 

 evidence of reproductive activity 

 was observed. 



Discussion 



A decline of CPUE from the begin- 

 ning until the end of the fishing sea- 

 son has been reported for other 

 Panulirus argus fisheries (Warner 

 et al. 1977, Lyons et al. 1981). How- 

 ever, in the fishery of Bahia de la 

 Ascensi6n, the decline from the first 

 month of the season to the second 

 is sharp. Eggleston et al. (1990) sug- 

 gest that casitas enhance survivor- 

 ship of juvenile lobsters by pro- 

 tecting them from their predators, 

 hence increasing lobster production. 

 Thus, during the closed season, in 

 the absence of fishing mortality, it 

 is possible that the aggregation 

 effect of casitas on juvenile lob- 

 sters, in conjunction with recruit- 

 ment by rapid growth, result in the 

 catch from a casita being greater 

 during the first month of the season 

 than during the remainder of the 

 season. 



The high level of recaptures during both the 1985-86 

 and 1986-87 seasons suggests a high level of fishing 

 mortality on the population in Bahia de la Ascension. 

 The failure to recapture any of the animals tagged in 

 1985 during the tagging program in 1986, and the fact 

 that only four were recaptured during the fishing 

 season in 1986-87, may reflect tag loss, high natural 

 mortality, or a strong emigration from the bay. The 

 latter is supported by the movements of the recaptured 

 lobsters. 



We could not separate fishing mortality from natural 

 mortality because there appeared to be both recruit- 

 ment by growth of small lobsters throughout the season 

 as well as immigration onto the casitas from other 

 areas. This is sustained by the monthly size composi- 

 tion of the catch by the fishery (Fig. 2). Those catches 

 showed a nearly constant size distribution, with a mode 

 near the minimum size limit, indicating recruitment by 

 growth to the fishery throughout the fishing season. 



(a) 



^1 } Punta 

 Pajaros 



(c) 



(b) 



(d) 



Figure 1 1 



Recorded movements of Panulirus argus tagged in sampling zones II, III, IV, and 

 VI in Bahia de la Ascension, 1986-87. Shaded areas denote sampling zones; arrows 

 indicate direction of movements and arrowheads the sites of recapture. Numbers in- 

 dicate lobsters that moved in each direction from denoted sampling zone. 



The estimates of the growth parameters by the 

 Fabens' method showed great variability (Table 2a), 

 which could be interpreted in two ways: (1) Lobster 

 growth differed greatly interanually, or (2) the pro- 

 cedure yielded unreliable estimates. Palmer et al. 

 (1988) suggested that the Fabens method does not ex- 

 plicitly model individual variability in growth (e.g., Fig. 

 8), and that it produces inconsistent estimates of the 

 asymptote of growth. 



Alternatively, the maximum likelihood estimates of 

 the mean curves did not show great variability, so both 

 years could be pooled to obtain a final set of param- 

 eters. The reasonableness of the estimated parameters 

 was further confirmed by the fact that P. argus can 

 attain sizes much larger than the asymptotic sizes 

 estimated from the Fabens method (Sutcliffe 1957, 

 Munro 1974, Olsen and Koblic 1975, Farrugio 1975). 

 However, the tagged lobsters were mostly juveniles 

 and young adults as further demonstrated by the lack 



