All ami I'KRRYMAN: MOVEMENT AND SI'EEl) OF DOLl'HIN SCHOOLS 



000°, the school's swimming vector (OD) is 

 obtained by vector subtraction as shown. In this 

 case the swimming vector is 7.5 kn, heading 

 060°, and is the average swimming velocity be- 

 tween 0830 and 0845 h. Notice that the relative 

 motion line is defined by ranges and bearings 

 while the triangle at the center is composed of 

 speed vectors, where, for convenience, 10 kn is 

 defined as having magnitude to 2 on the mile 

 scale. 



RESULTS 



Figure 2.— Example of relative motion plot and calculation of 

 school swimming vector. 



relative motion between 0830 and 0845 h is 

 equivalent to a relative velocity vector of 9.1 kn 

 heading 134°. Projecting this vector (SD) onto 

 the ship's vector (OS), which is 10 kn heading 



Vessel Avoidance 



We were able to follow eight dolphin schools 

 with the ship and helicopter (Table 1). The 

 species were the spotted dolphin, the spinner 

 dolphin, and the striped dolphin, S. coeruleoalba. 

 All eight schools continuously adjusted their 



Table 1.— Summary of dolphin schools observed from helicopter. 



School Species 



Date and 

 position 



Local 



time 



(h) 



Initial 



Range 



(nmi) 



Speed 

 (kn) 



School' 

 size 



Behavior relative to distance from ship 2 



1 



Stenella 

 attenuata 



Stenella 

 attenuata 



I 10°00'N \ 

 V108°01'W/ 



/ 9°30'N \ 



\109°39'W/ 



0950 5.6 5.8 100 At 3.5 mi ship changes course and school increases speed to 8 3 kn. 



Between 1.9 and 2.6 mi school veers 40° to right across ship's path; 

 as ship's path is crossed, school alters course again to head directly 

 ahead of ship. At 2 mi school is in 2 groups running very purposefully 

 with little intraschool deviations. 



Cruising smoothly at 5-6 kn with little splashing during most of vessel 

 approach; strong evasive maneuvers at 100 m by group closest to ship. 



Two species incompletely mixed; many adults and juveniles in school. 

 0938 6.2 4.3 50 School initially "porpoising" gently as a loose aggregation, moving 



away to ship's right. 



At ca. 6.0 mi ship changes course; school veers 108° to left, acceler- 

 ating to 5.8 kn 



At ca. 5.0 mi school turns left again, still moving away at ca. 5.5 kn. 



At ca. 3.3 mi ship changes course and school accelerates to 6.3 kn 

 temporarily. 



Between 2.0 and 3.0 mi school turns more to left; still running smoothly 

 at 5.5 kn with little splashing. 



As ship passes 2.0 mi to right of school, it veers sharply left, con- 

 tinuing on almost opposite course as ship 



Individuals bunching up at 18 mi. At times school composed of 4 groups. 



At 1.5 mi school speed is 8.3 kn. 



At 9 mi school running smoothly ahead of ship; a portion breaks off to 

 right at ca. 100 m distance 

 0935 5 2 6 4 15 School initially seen under ca 100 feeding boobies (Sula sp .). moving 



away from ship 



At ca. 4.3 mi school accelerates to 7.8 kn then slows to 6.2 kn. 



At 3 5 mi school turning to right. 



Between 2 and 3.0 mi school swimming smoothly at ca. 5.0 kn; birds 

 flying, rafting, or diving; most working ahead of school; later they 

 form 2 large rafts behind school. 



By 1.5 mi school speed has increased to 7.2 kn. 



As school passes to left of ship at ca 1.5 mi, it accelerates to 13 kn 

 and veers to left. Birds have ceased feeding inside of 2 mi distance. 



School begins strong evasive maneuver at ca. 1/4 mi distance. 



323 6 2 3 8 350 Initially detected as bird target by radar 



Between 4 2 and 4 9 mi school changes course sharply away from ship, 



increasing speed to 4.6 kn, then slowing to 2.9 kn. 

 At 3.0 mi much splashing in running school; some long, flat leaps seen. 



School becoming more scattered Birds toward rear of school; later are 



scattered over school. 

 At ca 3 2 mi ship makes 90° turn to left; school veers 94° to left and 



increases speed; much running leaps seen; by 3.0 mi school speed is 6.5 



kn. 

 Between 2 5 and 3 mi main group in school turns toward ship; moments 



later they reverse their course again. 



373 



