FOGARTY ET AL.: MOVEMENT OF AMERICAN LOBSTER OFF RHODE ISLAM) 



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0- 31- 61- 91- 121- ISl- 181- 211- 241- 2/1- JOI- 3jl- 361- j.390 

 30 60 90 120 150 180 210 240 270 300 330 360 390 

 DAYS AT LARGE 



FIGURE 8. — Distance travelled (x±l SE) as a function of time at 

 large for American lobster tagged and released on Cox Ledge, off 

 Rhode Island. Sample sizes are specified beside each mean with 

 an associated standard error. 



straight-line distance between release and recov- 

 ery sites indicated that these long distance mi- 

 grants travelled to the outer continental shelf 

 (Figure 9). 



Tagging experiments conducted on the outer 

 continental shelf revealed a shoal ward migration 

 in late spring and summer (Cooper and Uzmann 

 1971; Uzmann et al. 1977). The offshore migration 

 in late fall and winter observed in the present 

 study complements these findings and indicates a 

 seasonal interchange between areas. 



The mean vector angle for recovered tagged 

 lobsters was 154.8°(T) at the Cox Ledge site and 

 Rayleigh tests indicated a nonuniform distribu- 

 tion of returns (Table 2). The north-south vector 

 component was substantially higher than the 

 east-west component for the first 180 d at large, 

 reflecting the strongly directed offshore move- 

 ment. The relative magnitude of the north-south 

 and east-west vector components were more 

 nearly equal for lobsters at large over 180 d, indi- 

 cating little directed movement. This is reflected 

 in the nonsignificant mean vector bearing for 

 lobsters at large between 181 and 270 d (Table 2). 



A two-way fixed factor analysis of variance was 

 used to examine the effects of size and sex on 

 distance travelled for lobsters tagged and released 

 on Cox Ledge. Lobsters were grouped by release 

 size («90, 91-100, 101-110, 111-120, 121-130, ^131 

 mm CL) and sex (male, female, ovigerous female) 

 and the data were transformed (log;.x+l) prior to 

 analysis. No significant differences (P<0.01) were 

 noted by size, sex, or the size-sex interaction. 



Figure 9. — Straight line distance between release and recap- 

 ture sites for American lobster tagged and released on Cox 

 Ledge, off Rhode Island. Release location is a composite of four 

 release sites on Cox Ledge. Total distance travelled is noted for 

 tracks which are truncated bv borders. 



Low return rates (n=29) for lobsters displaced 

 from the Midshelf site to Cox Ledge prevented 

 detailed analysis of movement patterns. The dis- 

 placed lobsters were treated independently of the 

 lobsters tagged and released on Cox Ledge at all 

 levels of analysis. The mean distance travelled for 

 lobsters transplanted from the Midshelf site to 

 Cox Ledge was 41.6 km with an average of 274.7 d 

 between release and recapture. The mean vector 

 bearing for Cox Ledge-Midshelf lobsters was 

 170.5°(T); however, the hypothesis of a uniform 

 distribution of return directions was not rejected 

 (P<0.01) when the data were subjected to a 

 Rayleigh test. 



Return rates for lobsters tagged and released on 

 the Midshelf fishing grounds were also low, pre- 

 venting detailed analysis. The mean distance 

 travelled for 34 recovered lobsters was 18.2 km and 



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