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Fishery Bulletin 89(1), 1991 



of an inflection point in their mean weekly growth rate. 

 Thus, the estimated parameters may reflect growth 

 rates of immature lobsters only, and those of repro- 

 ductive adults could change the last part of the curve 

 (Fig. 9). 



Lyons et al. (1981), utilizing a method that involved 

 mean growth rates obtained from several authors, 

 estimated an age of slightly more than two years after 

 settlement as postlarvae for P. argus measuring 76 mm 

 CL, allowing for a nine-month larval period. With our 

 maximum likelihood results, and considering the same 

 nine-month larval period, the estimated age for a 

 76 mm CL lobster would be 2.5 years. Munro (1974) 

 produced a growth curve for P. argus based on data 

 from 156 lobsters tagged and recaptured in Florida and 

 Belize. His estimated age of one year after settling as 

 postlarvae for lobsters measuring 45 mm CL agrees 

 closely with the estimate obtained in the present study 

 by the maximum likelihood approach. Peacock (1974) 

 tentatively estimated an age of one year for 50mm CL 

 P. argus, as did Eldred et al. (1972) and Witham et al. 

 (1968). 



Therefore, the maximum likelihood approach utilized 

 in this paper seems to have provided a useful set of 

 growth parameters for juvenile and young adult 

 P. argus, with the additional advantage of separating 

 growth data between males and females. 



The few signs of reproductive activity in female 

 lobsters near the reef, in conjunction with small cara- 

 pace length, indicated that the lobster population in 

 Bahi'a de la Ascension was probably composed mainly 

 of juveniles. Lyons et al. (1981) found little evidence 

 of mating activity of P. argus in the shallow Florida 

 Keys, and they stressed that almost 90% of the spawn- 

 ing occurred at their reef and deep-water stations. 

 Peacock (1974), Davis (1975), and Kanciruk and Herrn- 

 kind (1976) also reported an absence of reproductive 

 activity in shallow bank or lagoon areas. 



The movements demonstrated by the tagging pro- 

 gram indicate a displacement of lobsters from shallows 

 toward deeper habitats offshore. This was also sup- 

 ported by the analysis of the size composition by zones 

 (Figs. 7, 8; Table 1), which indicated that the lobsters 

 were smaller in the innermost sampling zones com- 

 pared with those caught near or on the reef. Buesa 

 (1970) and Cruz et al. (1986) suggested that juvenile 

 P. argus in Cuba live in protected areas with seagrass 

 beds and move towards the outer reefs as they grow. 

 Other authors that mention similar movements for 

 juvenile P. argus are Peacock (1974) in Barbuda, Olsen 

 and Koblic (1975) in the U.S. Virgin Islands, Warner 

 et al. (1977), Davis (1979), and Lyons et al. (1981) in 

 Florida. 



Although northern and southern movements were 

 made by lobsters which left the bay, southerly move- 



ments predominated. In a three-year study of move- 

 ments of P. argus in Biscayne Bay, Florida, Davis 

 (1979) found southerly movements of tagged lobsters 

 during the first year, northerly movements in the sec- 

 ond year, and both northerly and southerly displace- 

 ments during the third. He concluded that juvenile 

 lobsters from Biscayne Bay are recruited into virtual- 

 ly the entire Florida fishery. The extent of the move- 

 ments made through deeper water by the lobsters 

 tagged in Bahi'a de la Ascension— and their final 

 destination— is still unknown, because from Tulum to 

 Mahahual (Fig. la) lobsters are fished only in the bays 

 and on the shallow parts of the reef. A winter migra- 

 tion, similar to that which occurs at the northeastern 

 end of the Yucatan Peninsula (Kanciruk and Herrnkind 

 1978), may take place in deeper waters outside the cor- 

 al reef that runs across the front of the bay. 



Small size, rapid growth, movements toward the reef 

 areas, and lack of reproductive activity all serve as 

 evidence that the population of lobsters in Bahi'a de la 

 Ascension is composed of juveniles. We hypothesize the 

 existence of a population composed of reproductive 

 adults off the coral banks of Bahia de la Ascension, an 

 area that is not currently being fished. 



The existence of adult stocks outside of the bay and 

 the output of lobsters from the bay into offshore deeper 

 areas are issues that need to be assessed for future 

 management plans. In addition, although casitas may 

 provide critical refuge for juvenile lobsters from their 

 natural predators (Eggleston et al. 1990), the long-term 

 effects of the casitas on the lobster populations, as well 

 as on the benthic communities associated with sea- 

 grasses and on the stability and structure of the 

 seagrass beds themselves, remain to be determined 

 through future field studies. 



Acknowledgments 



We acknowledge the field assistance of MariCarmen 

 Martinez, Fernando Negrete, Gabriel Carrasco-Zanini, 

 Alfredo Velazquez, Juan Garcia, Edith Zarate, David 

 Ortega, Carlos Rico, Alejandro Torres, and Jorge 

 Simonin. The first three also helped with data process- 

 ing. Mark Palmer, David Gutierrez, Nick Caputi, and 

 Norm Hall gave mathematical advice. William G. 

 Lyons, Alan Campbell, and two anonymous reviewers 

 greatly improved the manuscript. The study was sup- 

 ported by Universidad Nacional Autonoma de Mexico, 

 CSIRO-Australia, and Consejo Nacional de Ciencia y 

 Tecnologia de Mexico (Joint Project No. 140134D202). 

 Scientific fishing permits extended by the Fisheries 

 Secretary of Mexico made this study possible. We also 

 express our thanks to the fishermen of the several 

 cooperatives that assisted the study, particularly the 

 "Pescadores de Vigia Chico." 



