FISHERY BULLETIN: VOL. 78, NO. 3 



METHODS 



In 1974 and 1975, 3,063 lobsters (55-176 mm CD 

 were tagged and released at five general locations 

 off the Rhode Island coast and on the adjacent 

 continental shelf (Figure 1). 



Lobsters were tagged using the sphyrion anchor 

 tag(Scarratt andElson 1965). The tag consisted of 

 an encoded yellow plastic tube (2 mm in diameter) 

 attached to a stainless steel anchor by a monofila- 

 ment thread. The anchor was inserted with a 

 hypodermic needle into the right or left dorsal 

 extensor muscle of the lobster through the mem- 

 brane posterior to the margin of the carapace. 

 Carapace length, sex, molt status, and physical 

 condition were recorded for each tagged lobster. 

 We obtained lobsters used in tagging experiments 

 directly aboard commercial lobster vessels. 

 Lobsters were tagged at sea and released as close 

 to the point of capture as possible. However, on 20 

 December 1974, 231 lobsters captured on the mid- 

 continental shelf (Midshelf) were released on Cox 

 Ledge. This displacement ( =60 km) was necessary 



to avoid several foreign trawlers which moved into 

 the area during tagging operations. 



Rewards of $2 for the return of the tag alone and 

 $5 for the return of the lobster and tag were paid. 

 Information on the date and location of capture 

 were requested for each recapture. The study was 

 publicized through the local news media, posters 

 describing the study distributed to shellfish deal- 

 ers, and personal contact with fishermen. 



For detailed evaluation of directional compo- 

 nents of movement we followed the approach of 

 Saila and Flowers (1968). The specific test statis- 

 tics and directional components computed were 



Mean vector angle 



= arc tan 



Lir cos ej 



Mean square dispersion coefficient (km^/d) 



-4 [^ 



r^ ( Vr cos e)^ + ( Vr sin O)^ 

 t It 



] 



North-south directional 

 component (km/d) 



V = 



^r cos 9 



NARRAGANSEtT BAY 



^ SAKONNET RIVER 



RHODE ISLAND 

 SOUND 



^' 



o 



cox lEDCE 



MIDSHELF O 



Figure l . — Location of tagging sites for American lobster in the 

 coastal waters of Rhode Island and on the adjacent continental 

 shelf 



East-west directional 

 component (km/d) 



Rayleigh test statistic 



y., _ ^r sin 6 



Z = RVn 



where R = [{^ sin 6)2 + ( V cos 9)2] 

 n = number of individuals 

 9 = direction of travel from an arbitrary 

 reference point 

 t = time in days from release 

 r = straight line distance (km) of travel. 



All angles are presented as deviations from true 

 north (°T). The Rayleigh test is a test for uniform 

 concentration of points around a circle of unit 

 radius (Batschalet 1965). 



The mean square dispersion coefficient is a mea- 

 sure of undirected or random movement based on 

 diffusion theory (Beverton and Holt 1957; Jones 

 1959, 1966). The dispersion coefficient is a com- 

 pound parameter dependent on both rate of travel 

 and the mean distance travelled without di- 

 rectional change (Jones 1959). The quantities V 

 and V indicate directional or nonrandom compo- 

 nents of movement. These parameters measure 

 the mean rate of group movement of tagged indi- 

 viduals in the north-south and east-west planes. 



772 



