1 



21 Nov. (initial release) 



2 



22 Nov. 



3 



23 Nov. 



4 



24 Nov. 



5 



25 Nov. (end of radio track) 



6 



6 Dec. (recontact) 



7 



7 Dec. (end 2nd track) 



8 



10 Dec. (recontact) 



Figure 4. — Cruise track of chartered purse seiner Queen Mary while 

 tracking movement of school of radiotagged spotted dolphins, Sten- 

 ella attenuata, in November-December 1971. Heavy lines represent 

 portions of the cruise track when radio contact was maintained with 

 the school. The lines represent movements of the vessel, not necessar- 

 ily the exact route of the radio-tagged animals. 



fore completion of the net circle. After the set, A and D 

 were followed until 2200 when they separated. Male D 

 was followed, with a faint signal in the background from 

 A, until 1020 on 24 November (set 5). Net distance trav- 

 eled in this 24-h period was 69 n.mi., but actual distance 

 traveled was about 110 n.mi. (Fig. 4). At this time, A and 

 D had reconverged, but the set was made on the portion 

 of the school containing D. Animal D again eluded cap- 

 ture in the seine. A and D rejoined after the set and were 

 followed until 0700 on 25 November when the track was 

 terminated because of an approaching storm. Net dis- 

 tance traveled during this 22-h period was approxi- 

 mately 75 n.mi. The school had doubled back and was 

 heading north on almost exactly the same path it had fol- 

 lowed south 3 days before. Total net distance traveled 

 during the 110 h of the 5-day radiotrack was only about 

 75 n.mi., about one-fourth of the actual distance trav- 

 eled. Maximum distance between any two points on the 

 track was about 160 n.mi. 



On 6 December, 11 days and approximately 285 n.mi. 

 distance from termination of the first track, signals from 

 both of the males (A and D) were picked up at 1255 and 

 followed until 0750 on 7 December when strong signals 

 were received from A in a school of <30 spotted dol- 

 phins. The school was chased to allow close approach and 

 a good estimate of size, but no net set was made, and the 

 school was not further followed. Net distance traveled 

 during this 19-h second radiotrack was about 75 n.mi. 

 Three days later, on 10 December, at 0925, signals were 

 again received from A and D, and, this time, also from 



the female C, which had not been heard from since sepa- 

 rating from the males on 23 November. The males and 

 females were again segregated within the school. The 

 school was not set on or followed after this recontact, and 

 the research cruise ended shortly thereafter. Net distance 

 traveled by the school between initial release and last 

 contact (19 days) was 357 n.mi. (19 n.mi./day, south- 

 southeast). 



RESULTS AND DISCUSSION 



Of 3,712 tags released from 1969 through 1976, 104 had 

 been returned as of 1 January 1977 (Tables 3, 4). Tags 

 were recovered only from spotted dolphins (97) and spin- 

 ner dolphins (7). Time at liberty ranged from 1 h and 40 

 min to 1,478 days for S. attenuata and from 15 h and 48 

 min to 776 days for S. longirostris. Minimum distance 

 traveled (distance between release and recovery loca- 

 tions) ranged from 7 to 582 n.mi. for S. attenuata (Fig. 5) 

 and 12 to 275 n.mi. for S. longirostris (Fig. 6). Details of 

 returns are presented in Tables 4, 5. Returns are suffi- 

 cient for the spotted dolphin to allow some analyses 

 based on these and on the results of radiotagging. 



Short-Term Movements 



Twenty-six tagged spotted dolphins were recaptured 

 within 2 days (48 h) after release (Fig. 7). Longer term re- 

 coveries were not included in the analysis because of the 

 increasing potential for bias caused by the animals 

 doubling back on themselves (see results of radiotagging 

 experiment above). A linear regression line fitted to the 

 data has a slope indicating an average movement rate of 

 about 1.2 n.mi./h (about 30 n.mi./day). 



The results of the radiotagging experiment indicate 

 daily movement rates of similar scale (Fig. 4), yielding 

 estimates of net daily travel rate ranging from 5 to 89 

 n.mi. and an average of 54 n.mi./day (Table 6), as com- 

 pared with the estimate of about 30 n.mi./day based on 

 short-term tag returns. The former can be assumed to be 

 less affected by the "doubling back" factor. 



Long-Term Movements 



A plot of minimum distance traveled on time at liberty 

 for all tag returns shows maximum movement of 500 to 

 600 n.mi. (Fig. 8). The data may have a periodic com- 

 ponent. Average minimum distance traveled is 100 n.mi. 

 for 10- to 50-day returns (n = 21) and 274 n.mi. for 50- to 

 200-day returns (n = 12) but only 93 n.mi. for 200- to 400- 

 day returns (n = 15). A major question in interpreting 

 these results is that of recovery effort. Tags are recov- 

 ered during the fishing operation. Was there signi- 

 ficantly more fishing effort in areas <200 n.mi. from 

 areas in which tags were released 200 to 400 days earlier 

 than in areas more than 200 n.mi. from areas of release? 

 In other words, could the data reflect periodic fishing ef- 

 fort rather than periodic movement of dolphins? In an at- 

 tempt to settle this question, we examined, for each of 

 the 50- to 200-day returns (12) and each of the 200- to 



