HUNT ET AL.: EXPOSURE AND CONFINEMENT ON SPINY LOBSTERS 



posure periods up to 1 h resulted in corresponding 

 increases in mortality. Similar mortality has been 

 observed in the Western Australia spiny lobster 

 (Panulirus cygnus) fishery (Brown and Caputi 1983; 

 Brown et al. in press). In that fishery, undersize 

 lobsters are not used as bait but are often retained 

 aboard vessels for varying periods during the sort- 

 ing process. Tb test effects of that practice, Austral- 

 ian lobsters were tagged, held aboard vessels for 0, 

 Vi, V2, 1, and 2 h, and then released. Recapture rates 

 were markedly lower in exposed groups than in con- 

 trols. As in our experiments, results from exposure 

 times >1 h were similar to those of 1 h exposures. 



The greatest rate of mortality to Panulirus argus 

 in our tests occurred during the first week follow- 

 ing exposure (Fig. 2). Although physiological causes 

 of mortality have not been determined, several fac- 

 tors may be involved. Dehydration due to desicca- 

 tion may affect survival, but lobsters dampened at 

 V2 h intervals died at rates similar to those left un- 

 attended. One effect of exposure is to dry gills 

 (Anonymous 1980), which may result in respiratory 

 problems. Dehydration and gill damage may cause 

 mortality directly, but more likely are contributory 

 factors to physiological stress caused by buildup of 

 toxic compounds in the blood. Handling stress has 

 been demonstrated to cause temporary acidic con- 

 ditions in the blood of European lobsters, Homarus 

 vulgaris (McMahon et al. 1978). After reimmersion 

 in seawater, lobsters should rehydrate fairly quick- 

 ly, but effects of physiological stress are likely to 

 linger. 



Contrary to prior expectations, mortality rates of 

 dampened lobsters did not differ significantly from 

 those left unattended (dry). Dampening also failed 

 to enhance survival of the northern lobster, Homarus 

 americanus (McLeese 1965). McLeese suggested 



Table 3.— Results of Wilcoxon Two Sample Tests (Z 

 values) from comparisons of mean weekly (1-4) mor- 

 tality rates for various treatments at Florida Bay 

 (Bay) and Atlantic Reef (Ocean) locations. 



P *S 0.05; * * = P « 0.01 ; * * * = P < 0.001 . 



that a relationship existed between metabolic rate 

 and mortality. An increase in metabolic rate and con- 

 current more rapid depletion of reserves may have 

 offset advantages of increasing moisture by dampen- 

 ing during our experiments as well. 



Exposure was probably the principal cause of mor- 

 tality among bait lobsters during our tests in Florida 

 Bay. However, a small but distinctly greater level of 

 mortality among all lobsters, including controls dur- 

 ing weeks 1-3 and a marked increase in mortality 

 during week 4 at the ocean site, suggest that other 

 factors in addition to exposure were responsible for 

 mortalities there (Figs. 1, 2). When average mortality 

 rates of controls (Table 1) are subtracted from overall 

 average mortality rates of exposed lobsters, resul- 

 tant values (18.6%, Florida Bay; 18.3%, Atlantic 

 reefs) are nearly equal and probably represent the 

 rates of mortality actually ascribable to exposure at 

 each site Thus, effects of exposure were similar 

 regardless of where traps were placed. 



Mortality due to other effects related to confine- 

 ment evidently do vary depending upon locations 

 where traps are placed, especially if confinement 

 periods are lengthy. Increased mortality rates such 

 as those we observed during week 4 at the Atlantic 

 reef site may result from starvation. Lyons and Ken- 

 nedy (1981) presented evidence of weight loss and 

 starvation among lobsters confined at densities of 

 3 and 5/trap in Florida Bay for 8 wk. Rate of weight 

 loss increased during week 4 among lobsters at den- 

 sities of 5 but did not increase rapidly until week 6 

 among lobsters confined at densities of 3. Those tests 

 were conducted in the same portion of Florida Bay 

 where present exposure tests were conducted, an 

 area characterized by muddy sand overlain by sea- 

 grass beds. A disparity in available food organisms 

 between this area and that where oceanside tests 

 were conducted may explain differences in mortal- 

 ity during week 4. 



Seagrass beds in Florida Bay are lush and heavi- 

 ly covered with epibionts (J. H. Hunt, pers. obs.). 

 These epibionts serve as food for larger organisms 

 which in turn are appropriate food for Panulirus 

 argus. Snails in the genera such as Modulus, Turbo, 

 Astraea, and Cerithium and crabs in the genera 

 Mithrax and Pitho are abundant in these grass beds 

 and are frequently seen within or clinging to sides 

 of lobster traps. All of these also occur commonly 

 in stomach contents of P. argus in south Florida (W 

 G. Lyons, pers. obs.). At the ocean site, grass beds 

 are sparse and patchily distributed, and fewer 

 organisms enter traps from the surrounding sand. 

 It seems reasonable to suppose that the weight loss 

 observed to occur among lobsters confined near lush 



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