FISHERY BULLETIN: VOL. 80. NO. 2 



directions of swimming, by small increments, so 

 that the distance between the school and the 

 ship's projected track tended to increase contin- 

 uously with time. The schools were either 

 already proceeding on courses directed away 

 from the ship when first sighted or made sharp 

 course changes away from the vessel soon after. 

 Several schools were moving off at relatively 

 high speed when first seen. All the schools were 

 evidently avoiding the ship. The behavior that 

 indicated avoidance is summarized in Table 2 

 for each school. It appeared that avoidance be- 

 havior sometimes had begun when the school 

 was still 6 or more nautical miles away from 

 the ship. 



Sufficient positioning data were collected 

 from six of these schools to prepare diagrams of 

 their movement relative to the approaching ship 

 (Figs. 3, 4). The first school, school 1, is not 

 plotted because frequent course changes by the 

 ship during its tracking made relative move- 



FlGURE 3.— Relative movement plots of five schools (nos. 2, 3, 4, 

 6, 7), showing the apparent motion as seen by a shipboard 

 observer. Dotted lines are by dead reckoning. 



ment difficult to portray. The path of relative 

 movement of any of these schools, drawn by 

 connecting the sequential series of radar fixes of 

 the school as the ship moved forward, does not 



Table 1.— continued. 



School Species 



Date and 

 position 



Local 

 time 

 (h) 



Initial 



Range 



(nmi) 



Speed 

 (kn) 



School' 

 size 



Behavior relative to distance from ship 2 



0953 



Stenella 

 attenuata 



12-3-76 

 ca. 

 °31'N 

 °30'Wj 



1032 



/ 9°31'N \ 

 \110°30'wJ 



Stenella 

 attenuata 



+ 

 Stenella 

 longirostris 



I 10°00'N \ 

 \110°30'W / 



1440 



Stenella 

 coeruleoalba 



12-2-76 

 r 10°27'N 1 

 ,110°01'W< 



1420 



At 2.5 mi individuals begin to bunch up; school in form of large arc with 

 some scattered animals on the sides; birds no longer feeding 



At 1 6 mi school is again scattered. Within 5 mi parts of school breaking 

 away from ship's path; birds rafting nearby. 



5.8 ca 2 6 300 Initially seen with many birds ahead and to right of school. School 



speed is ca. 2.6 kn. 

 At 3.3 mi school changes course sharply away from ship and speed accel- 

 erates. Animals running with compact ranks at rear of school; few birds 



over school now. 

 At 3.0 mi school running smoothly at ca. 8.4 kn. 

 At 2.2 mi individuals appear confused, going in various directions within 



oval shaped school 

 At 2.0 mi a group temporarily heads toward ship before reversing 



course; school speed is 9 3 kn. 

 At 06 mi many circuitous movements seen among small subgroups 



School passes to ship's left; all individuals uniformly running from ship 



at 8-9 kn; birds rafting ahead 

 Ship turns toward school at ca. 0.5 mi; school splits ahead of ship at 



ca 200 m; each dolphin species goes to different side of ship 



6.9 ca. 10.0 40 School initially seen as running, oval mass moving off at ca 10 kn with 



much splashing. 

 At 6.5 mi school is in 2 groups moving smoothly in arc with little splashing 

 At 5.7 mi school is in 2 groups moving smoothly at 8 5 kn 

 At 5.1 mi school is composed of a dense and a scattered section, many 

 direction changes among subgroups School speed is down to 7 kn 

 At 4.5 mi school is scattered; composed of 3 large groups; many direction 



changes seen; speed is ca. 90 kn again 

 Between 3.5 and 4.0 mi school speed decreases to 7.6 kn then increases to 

 9 3 kn as school begins passing to ship>'s left. 

 36 8.8 150 Initially swimming smoothly at ca. 8.8 kn with little splashing, scat- 



tered individuals at rear of school. 

 At ca. 3.0 mi school still holding similar course with speed of ca. 7.0 



kn; 50-70 birds over school 

 At 2.4 mi ship changes course and school also changes course and in- 

 creases speed; birds scattered over the scattered school. 

 At 1.4 mi school running smoothly in loose groups, going ca 6.0 kn 

 At <1.0 mi smoothly running school is scattered by ship. 



9 65 A leaping, loosely aggregated school at 9 mi 



At 0.7 mi school running with increasing speed as ship turns toward school 

 At 1/4 mi school forming an arc ahead of ship 



Estimated from aircraft, 

 distances and behavior from radar ranging and bearing, interpolation of movement trajectories, and field notes. Distances in nautical miles. 



374 



