Occurrence and seasonal variations 

 of spiny lobsters, Panulirus argus 

 (Latreille), on the shelf outside Bahia 

 de la Ascension, Mexico 



Enrique Lozano-Alvarez 

 Patricia Briones-Fourzan 

 Fernando Negrete-Soto 



Universidad Nacional Autonoma de Mexico 



Instituto de Ciencias del Mar y Limnologia, Estacion "Puerto Morelos" 



Ap Postal I 152. Cancun, Q.R 77500 Mexico 



The spiny lobster, Panulirus argus, 

 is one of the most valuable fishery 

 resources on the Mexican Caribbean 

 coast (Secretaria de Pesca, 1987). 

 Lobsters are caught with traps and 

 tangle nets, as well as by SCUBA 

 diving, only on the shelf around Isla 

 Mujeres and Isla Contoy (Fig. 1A), 

 at significantly greater depths than 

 elsewhere on the coast (Seijo et al. 

 1991). From Puerto Morelos to 

 Xcalak, where the continental shelf 

 is extremely narrow, lobsters are 

 captured mainly by skin diving in 

 the shallow coral reef and lagoon 

 areas (Lozano-Alvarez et al. 1991a). 

 In Bahia de la Ascension (Fig. 

 IB), the fishery for P. argus is based 

 on the use of artificial shelters, 

 called "casitas." Casitas are de- 

 ployed on the bottom and the lob- 

 sters sheltering beneath them are 

 caught by skin-diving fishermen. 

 Both casitas and the fishing method 

 are thoroughly described elsewhere 

 (Lozano-Alvarez et al. 1989, 1991a; 

 Briones et al. in press). Casitas are 

 installed only within the bay, but 

 some fishermen also skin dive for 

 lobsters in the shallow coral reefs 

 adjacent to the bay. No lobster 

 fishing is conducted on the coastal 

 shelf outside the bay deeper than 

 15 m. Only the tails are used. Tails 

 are graded according to weight, 

 packed in 10-pound (4.65 kg) boxes, 

 and frozen. Fishing regulations in- 

 clude a minimum size limit of 13.5 



cm tail length (=74 mm carapace 

 length, CD, a prohibition on the 

 catching of egg-bearing females, and 

 a closed season from 1 March to 30 

 June. 



In 1985-87, results from a tag- 

 ging program showed that the spiny 

 lobster population within the bay 

 comprised mostly juveniles and su- 

 badults (Lozano-Alvarez et al. 

 1991a). Growth of lobsters in the 

 bay was fast, and they moved from 

 the bay area towards the coral reefs 

 as they grew. No evidence of repro- 

 ductive activity in bay lobsters was 

 found (Lozano-Alvarez et al. 1991a). 

 Size of onset of sexual maturity is 

 =80 mm CL, but females do not be- 

 come fully mature until approxi- 

 mately 90mm CL (Fonseca, 1990). 

 This raised the hypothesis of the 

 existence of the reproductive seg- 

 ment of the population on the shelf 

 outside the coral reef, at greater, 

 currently unfished depths. Lozano- 

 Alvarez et al. (1991a) stressed the 

 need to test this hypothesis for fu- 

 ture management plans. 



In this paper, we present evidence 

 of the occurrence of adult reproduc- 

 tive P. argus on the continental shelf 

 outside Bahia de la Ascension, and 

 discuss seasonal variations in abun- 

 dance and some biological aspects 

 of this segment of the population, 

 as well as its potential importance 

 as a refugium in space. The fisheries 

 aspects of the study were published 



elsewhere (Lozano-Alvarez and 

 Negrete-Soto, 1991). 



Methods 



Bahia de la Ascension (Fig. IB) 

 is a large (=740 km 2 ) and shallow 

 (<6m deep) bay, bordered by man- 

 groves and grass swamps. A sub- 

 stantial part of the bottom of the 

 bay is covered with seagrass 

 (mainly Thalassia testudinum) and 

 dense aggregations of red and green 

 algae (Briones et al., in press). A 

 coral reef tract exists along its 

 mouth, protecting the inner waters 

 of the bay from wave surge. The 

 bay is a nursery area for P. argus 

 (Lozano-Alvarez et al. 1991a). 



Fishing operations for spiny lob- 

 sters were carried out on the conti- 

 nental shelf outside the coral reef 

 tract (Fig. IB) during two different 

 seasons, summer ( 11 July-10 Sep- 

 tember 1989, six fishings), and win- 

 ter ( 14 November 1989-27 Febru- 

 ary 1990, five fishings). Standard 

 lobster traps of the kind used by 

 fishermen at Isla Mujeres were set. 

 The traps were rectangular, mea- 

 suring 121 X 91 X 40cm. The 

 frame, built with 12-mm diameter 

 rod, was covered with plastic coated 

 galvanized wire mesh (5 X 2.5cm), 

 and an entrance was left on one of 

 the small sides. Traps were baited 

 with cow hide. 



A maximum of 39 traps was in- 

 stalled in any fishing operation, in 

 lines parallel to the coral reef. The 

 continental shelf in front of the bay 

 is narrow, not exceeding 4 km from 

 the coast. Complex reefs exist in 

 this area at depths of <10m and 

 from 30 to 40 m (Jordan-Dahlgren 

 et al., in press). After 40 to 60m 

 the slope becomes very steep, rap- 

 idly reaching depths in excess of 

 400 m. Echosounding was used to 



Manuscript accepted 17 May 1993. 

 Fishery Bulletin, U.S. 91:808-815 ( 1993) 



