Taylor and Hoenig- Growth per molt of Chionoecetes opilio from Newfoundland 



755 



707 



5 10 15 20 25 



MOLT INCREMENT (mm) 

 Figure 2 



Frequency of occurrence of growtli increments for recaptures of 

 Chionoecetes opilio from Conception Bay. 



precise to within 3 mm (Restrepo 1989, Hunt and 

 Lyons 1986, Little 1972). If measurement errors oc- 

 cur at both the time of tagging and the time of re- 

 capture, then errors as large as 5 or 6 mm might be 

 encountered. 



Conception Bay 



We recovered 850 tagged animals from Conception 

 Bay. Of these, 751 had measured increases in size of 



3 mm or less; three had increases of 4-5 mm; the re- 

 maining 93 animals had increases of at least 6 mm (Fig. 

 2). None of the three animals with molt increments of 



4 or 5 mm were particularly small (premolt sizes: 92, 

 96, 99 mm). Consequently, these animals would not be 

 expected to have particularly small increments. Their 

 times at liberty were 325, 187, and 157 days, respec- 

 tively. We assume that the 93 animals with increments 

 of 6 mm or more molted at least once, and none of the 

 other animals molted. The average time at liberty for 

 animals which did not molt is under a year (x 322 

 days, median 251 days, range 6-1598 days; Fig. 3). 



The size at recapture of Conception Bay crabs which 

 molted was plotted against the size at tagging, and two 

 distinct linear clouds of points were apparent (Fig. 4). 

 The line indicating a 17% increase in size appears to 

 separate the two clouds nicely. A reasonable working 

 hypothesis is that the lower cloud consists of animals 

 which molted once, while the upper cloud consists of 

 animals which molted twice. One animal in the two-molt 

 group was at liberty for only 29 days and was tagged 

 and recaptured in a hard-shelled condition. Animals re- 

 main soft-slielled for 2-3 months after molting, and 

 soft-shelled animals cannot molt (Taylor et al. 1989). 



' 'y- m 



»: 



txlPxlf:<]k-;1r;^F:?lF:<lF?>l. 



D4fS AT LIBGRTy 



Figure 3 



Histograms of times at liberty for Conception Bay Ch itvioereti's npUio. 

 Upper figiire corresponds to tlie upper cloud of points in Figure 4. 

 i.e.. to animals believed to have molted twice. Middle figure corre- 

 sponds to the lower cloud in Figure 4. Lower figure corresponds to 

 recaptured animals which had not molted while at liberty. 



For this reason, this animal was eliminated from fur- 

 ther consideration. 



The times at liberty for 81 of the 92 Concepti(.)n Bay 

 animals which molted ranged from 18 to 1618 days. 

 (Exact times at liberty could not be determined for 1 1 

 animals.) However, the mean time at liberty for the 

 hypothesized two-molter group was approximately 

 twice as long as for the single-molter group (828 vs. 

 468 days) and there was little overlap in the distribu- 

 tions of time at liberty for the two groups (Fig. 3). 

 Animals which did not molt were at liberty for an 

 average of 322 days. Although there is little informa- 

 tion in the literature on intermolt periods for snow 

 crabs, it is believed that crabs approaching commer- 

 cial size molt once per year (Robichaud et al. 1989) and 



