NOTE Lozano-Alvarez et al.: Occurrence and seasonal variations of Panulirus argus 



dent populations of P. argus has been suggested in the 

 Bahamas (Kanciruk and Herrnkind, 1978; Herrnkind 

 and Lipcius, 1989) and the Dry Tortugas (Davis, 1974). 



In contrast, the greater abundance of lobsters on 

 the shelf during the winter, in addition to their 

 smaller mean size and recently molted carapaces, 

 indicates a recent recruitment of subadult lobsters 

 to the deep habitat. The recruits likely originated in 

 the bay, from where they exited in pulses, as sug- 

 gested by the large number of lobsters caught in two 

 fishings (Table 1). These two fishings were conducted 

 immediately after the passage of two severe cold 

 fronts. Offshore movements of P. argus associated 

 with cold fronts have been documented in other parts 

 of the Caribbean and Florida (Herrnkind, 1980). 

 Moreover, catches increase notably in winter in the 

 deep fishery off Isla Mujeres, whereas catches from 

 more shallow areas, such as Bahia de la Ascension 

 and Banco Chinchorro (Fig. 1A) decline at that time 

 of year (Lozano-Alvarez, 1992). However, lobsters 

 moving along the coast (Davis, 1979; Gregory and 

 Labisky, 1986; Fonteles-Filho and Correa-Ivo, 1980; 

 Herrnkind, 1980) could also account for the greater 

 abundance found on the shelf. Some lobsters tagged 

 in Bahia de la Ascension were recovered at locations 

 several kilometers to the north and south of the bay 

 (Lozano-Alvarez et al. 1991a). The extent of these 

 movements along the offshore depth contours re- 

 mains unknown, and warrants further investigation. 



In contrast to the sex-ratio in our shelf samples, 

 females outnumbered males in offshore P. argus popu- 

 lations in Florida (Davis, 1974; Lyons et al, 1981; Hunt 

 et al., 1991M. Although in the Mexican Caribbean the 

 reproductive season spans from March to November, 

 with significant peaks in August-September (Fuentes- 

 Castellanos, 1988), fully mature females, particularly 

 those bearing eggs, were very scarce in our shelf 

 samples. However, considerable evidence exists sug- 

 gesting that traps fail to sample gravid females in 

 several species of spiny lobsters (Herrnkind, 1980). We 

 believe that gravid females were underestimated in 

 our shelf samples owing to the availability of natural 

 shelter. 



The distribution of lobsters in and outside Bahia 

 de la Ascension seems to conform to the known size- 

 related distribution of P. argus, that is to say juve- 

 niles inhabite shallow habitats (lagoons, bays) and 



1 Hunt. J. H., T. R. Matthews, D. Forcucci, B. S. Hedin, and R. D. 

 Bertelsen. 1991. Management implications of trends in the popula- 

 tion dynamics of the Caribbean spiny lobster. Panulirus argus, at 

 Looe Key National Marine Sanctuary. Final Rep., NOAA Office of 

 Ocean and Coastal Resource Management, Sanctuary Programs Div., 

 Contract 50-DGNC-6-00093, 81 p. 



adults dwelling on deeper reef habitats. However, 

 some large adult lobsters were found in the bay and 

 shallow adjacent reefs (Fig. 2A, Table 5). This fact 

 suggests that some adult lobsters return to inshore 

 habitats after their ontogenetic migration to deeper 

 habitats. Inshore movements of large P. argus have 

 been documented in Antigua and Barbuda (Peacock, 

 1974), Brazil (Fonteles-Filho and Correa-Ivo, 1980) 

 and Florida (Gregory and Labisky, 1986; Hunt et al., 

 1991). Hunt et al. (1991) suggested that these in- 

 shore movements are controlled by changes in behav- 

 ior associated with reproduction. 



The P. argus population in Bahia de la Ascension 

 and adjacent offshore areas is highly dynamic. Fishing 

 pressure on juveniles in the bay and near shallow reefs 

 is heavy (Lozano-Alvarez, 1992), but the closed season 

 is strictly observed, and no lobster fishing is conducted 

 offshore. Developing an alternative trap fishery off 

 Bahia de la Ascension would be impractical and costly, 

 because of the narrowness of the shelf, the complex 

 morphology of the bottom, the strong currents encoun- 

 tered in the zone, and the small and variable CPUE of 

 legal-sized lobsters obtained (Lozano-Alvarez and 

 Negrete-Soto, 1991). Consequently, the fishery will con- 

 tinue to be focused on the small-sized lobsters in the 

 shallow areas. 



Despite heavy fishing in the bay, we found evidence 

 of a winter offshore migration. Lozano-Alvarez (1992) 

 estimated a high emigration rate from the bay through- 

 out the year, so other offshore recruitment pulses may 

 occur at other times of the year (e.g., the closed sea- 

 son). Because of their large sizes, the resident females 

 on the shelf outside the bay have high indices of egg 

 productivity (Fonseca, 1990), and spawn more than 

 once in the reproductive season (Lipcius, 1986). Thus, 

 the unfished deep habitat outside the bay may bear 

 importance as a refugium in space (Campbell, 1989; 

 Caddy, 1990) for reproductive lobsters. 



Other deep, currently unfished lobster areas were 

 found offshore from Puerto Morelos (Lozano-Alvarez 

 et al., 1991b) and probably exist elsewhere along the 

 coast of Quintana Roo, particularly on the narrow shelf 

 from Puerto Morelos to Xcalak (see Fig. 1A), and in 

 many other areas of the Caribbean as well (e.g. Cuba, 

 Gonzalez et al., 1990). Their existence might serve to 

 mitigate, through the production of larvae, the pres- 

 sure exerted on more heavily fished stocks. We pro- 

 pose that the deep habitats on the shelf outside Bahia 

 de la Ascension should be left undisturbed as a nucleus 

 of protected spawning stock, regardless of the unknown 

 final destination of the larvae. We similarly encourage 

 the protection of other deep, currently unfished areas 

 throughout the Caribbean, as a means to preserve 

 groups of reproductive lobsters that contribute larvae 

 to the regional pool. 



