FISHERY BULLETIN: VOL. 78. NO. 3 



Table 3. — Movement statistics for lobsters released prior to 1 July 1975 and recaptured prior to 1 September 1975 (spring-early 

 summer) and lobsters released after 1 July 1975 and recaptured prior to 1 September 1975 (late summer). Data are pooled over release 

 locations in Narragansett Bay, Rhode Island Sound, and the Sakonnet River. See Table 2 for explanation of symbols. 



"P<001 



crease in directional movement in this period. Es- 

 timates of the mean square dispersion coefficient 

 also increased in the late summer period, indicat- 

 ing a general increase in activity levels. The rela- 

 tive magnitude of the increase in random move- 

 ment (as measured by a'^) was less striking than 

 the increase in directed movement, however ( Table 

 3). 



A two-way fixed factor analysis of variance was 

 used to determine the effects of size and sex on 

 distance travelled for each inshore release loca- 

 tion. The three inshore sites differed slightly in 

 release periods (Table 1) and were therefore 

 treated independently to eliminate any possible 

 seasonal effects. Lobsters were categorized on the 

 basis of release size (^60, 61-70, 71-80, 81-90, >91 

 mm CD and sex (male, female, ovigerous female). 

 No significant differences (P<0.01) were noted by 

 size, sex, or the size-sex interaction at any of the 

 three release locations. The data were treated 

 with a logg (x+1) transform prior to analysis. 



Offshore Locations 



In contrast to lobsters tagged at coastal loca- 

 tions, those tagged and released on Cox Ledge 

 exhibited extensive movements. The mean dis- 

 tance travelled was 41.6 km and the average time 

 between release and recapture was 235.3 d. Re- 

 turn rates were relatively high for the first 30 d, 

 and subsequently increased for lobsters at large 

 over 240 d (Figure 6). Of 157 lobsters recovered 

 with adequate information to evaluate move- 

 ments, 117 nA.b'7c ) were recaptured within 60 km 

 of the release site (Figure 7). Examination of dis- 

 persal as a function of time at large indicated 

 large-scale movements within 60-120 d of libera- 

 tion while recoveries after 240 d were progres- 

 sively closer to the release site (Figure 8). Plots of 



530' 



D 



cox LEDGE N = 157 



3 COX LEDGE- MIDSHELF 

 N = 29 



r-r 



rki,.41 



61- 

 VO 



1^0 180 210 240 

 DAYS AT LARGE 



2 70 100 330 360 390 



Figure 6. — Number of tag returns for American lobster re- 

 leased on Cox Ledge and lobster displaced from the Midshelf 

 tagging site to Cox Ledge (Cox Ledge- Midshelf) as a function of 

 time at large, Rhode Island vicinity. 



80- 



(rt60' 



3 



LU 



a. 



UJ 



m 



20' 



[ 1 COX LEDGE N=157 



J COX LEDGE- MIDSHELF 

 N=29 



5 1-' 8f)l-' 'ODn' 120i-' )40l-' -.160 ' 

 80 100 120 MO 160 



100 120 140 



DISTANCE TRAVELLED (km) 



Figure 7. — Number of tag returns for American lobster re- 

 leased on Cox Ledge and lobster displaced from the Midshelf 

 tagging site to Cox Ledge (Cox Ledge-Midshelf) as a function of 

 distance travelled, Rhode Island vicinity. 



776 



