Eggleston et al : Artificial shelters and survival of juvenile Panuhrus argus 



697 



JANUARY-1989 



BAY SITE 



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S 

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 o 



.10 

 .08 

 .06 

 .04 

 .02 

 O.OO- 



LOBSTER SIZE 



C3 SMALL 

 ENLARGE 



,! I 



m^ 



SHELTER 



NO SHELTER 



JANUARY-1989 



REEF SITE 



I 



.10 

 .08 

 .06 

 .04 

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 0.00 



SHELTER NO SHELTER 



SHELTER AVAILABILITY 



Figure 5 



Results of field tethering of Panulins argus at the 

 inner-bay and outer-bay sites during January 1989, 

 describing mortality as a function of lobster size (small 

 46-55mmCL; large 56-65mmCL) and shelter 

 availability (casita vs. no casita). Values are mean pro- 

 portional mortality ■ casita"' • d"' resulting from a 

 total of 18 lobsters tested. Vertical bars are ISE. 





H 



O 



cr 

 O 



Q. 

 O 



cr 



AUGUST-1989 



REEF SITE 



.10 

 .08 

 .06 

 .04 

 .02- 



0.00 



PTW 



DISTANCE FROM SHELTER (m) 



Ryan's Q multiple comparison test (Einot and Gabriel 1975) 

 as recommended by Day and Quinn (1989). 



Results 



Tethering experiments 



During January 1989, mortality of juvenile lobsters varied 

 significantly as a function of lobster size but not according 

 to site or shelter availability (i.e., tethered to casitas or 

 60-70 m away in seagrass) (Table la. Fig. 5). However, the 

 interaction effect of lobster size by shelter availability was 

 significant; this interaction effect was due to the significantly 

 higher mortality of small vs. large lobsters tethered in 

 seagrass, and by the significantly higher mortality of large 

 lobsters in casitas compared with those tethered in seagrass 

 (Table lb). 



At the outer-bay site in August 1989, mortality rates of 

 small juvenile lobsters varied significantly according to 

 distance from the casita (i.e., 0, 15, 30, and 70m away from 

 the casita) (Fig. 6; one-way ANOVA; F 5.89, df 3, P<0.02). 

 Lobsters suffered significantly higher mortality rates when 

 tethered 15 and 70 m away from casitas than when tethered 

 to casitas or 30m away from casitas (Fig. 6; Q Ryan's test, 

 experiment-wise error rate 0.05). 



Predator observations 



The visual census of potential lobster predators at the inner- 

 bay site during January 1989 indicated two predatory crab 

 species (stone crab Menippe mercenaria, and a portunid 

 Portunus spinimamcs) and two piscine predators (gray snap- 

 per Lutjanus griseus, and schoolmaster snapper L. apodus) 

 associated with the casitas (Table 2). No potential pred- 

 ators were observed in the vicinity of the no-casita stations. 

 Mixed schools of gray snapper and schoolmaster snapper 

 were typically found within 10 m of large casitas. Schools 

 associated with small and medium casitas were usually 

 located within 5 m of the casitas. Observed movements of 

 snappers were seldom more than 15-20m from the shelters. 

 Similarly, two snapper species predominated at the outer- 

 bay site during January 1989: mutton snapper L. analis and 

 yellowtail snapper Ocyurus chrysurus (Table 2). Casitas at 

 the outer-bay site also attracted octopus (Octopus spp.), 

 green moray eel Gymnothorax funebris, the stone crab 



Figure 6 



Results of field tethering of Panulirus argus at the 

 outer-bay site during August 1989, describing mortality 

 of small juvenile lobsters (46-5.5 mm CL) as a function 

 of distance from the casita (i.e., 0, 15, 30, and 70 m away 

 from the casita). Values are mean proportional mor- 

 tality ■ casita"' • d"' resulting from a total of 18 

 lobsters tested. Vertical bars are ISE. 



