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



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Discussion 



The impact of artificial shelters upon juvenile spiny 

 lobster survival varied both by lobster size and the 

 distance of unprotected lobsters from shelter. During 

 our January 1989 experiment, which emphasized the 

 effects of lobster size and shelter availability, large 

 lobsters (56-65 mm CL) survived better than small 

 lobsters (46-55 mm CL) in sparse-to-moderate-density 

 seagrass (Thalassia) 60m from casitas. Conversely, 

 small lobsters survived better than large lobsters when 



tethered beneath casitas. During our August 1989 ex- 

 periment, small lobsters survived better at casitas or 

 30 m away from casitas than 15 m or 70 m away. We 

 interpret these patterns in terms of the relative impor- 

 tance of shelter availability and body size upon lobster 

 survival, and then speculate on the influence of 

 artificial-shelter-associated predators and seagrass den- 

 sity relative to these patterns in lobster survival. 



We reemphasize that predation estimates based on 

 tethering are likely biased by the technique and may 

 not reflect natural predation rates. For example, 

 lobster dens which are normally abandoned at night 

 may become "traps" for tethered lobsters because they 

 cannot effectively flee and conspecifics are not available 

 to help detect and repel predators. However, preda- 

 tion rates on early juvenile Panulirus argus tethered 

 in open sand, seagrass, and algal habitats in Florida 

 Bay were similar both day and night (Herrnkind and 

 Butler 1986, Smith and Herrnkind 1992). Moreover, 

 most casita-associated predators are widely dispersed 

 among the seagrass flats at night in Bahia de la Ascen- 

 sion, Mexico (Eggleston et al. 1990). Thus, we feel that 

 the tethering technique is not only useful for compar- 

 ing relative rates of predation between different size- 

 classes of juvenile spiny lobster, but also for compar- 

 ing predation rates between representative benthic 

 habitats (e.g., crevices, algal clumps, seagrass). 



Results from our January 1989 experiment support 

 the hypothesis that large juvenile lobsters (56-65 mm 

 CL) attain a relative-size refuge from predation com- 

 pared with small juvenile lobsters (45-55 mm CL), and 

 that the relative importance of this size refuge varies 

 according to shelter availability. Increased predation 



