AU and l'KRKYMAN: MOVEMENT AND SPEED OF DOI.IMllN SCHOOLS 



TABLE 2. — Range and behavior when vessel avoidance was first seen. 



School number 



Species 



Range (nmi) 



Behavioral indication of vessel avoidance 



School rapidly swimming away from ship at 5.8 kn when first 



sighted from helicopter 

 As ship turned toward this school, the animals accelerated 



from 4.3 to 5 8 kn and turned away from the ship 

 School rapidly swimming away from ship at 6.4 kn when first 



sighted from helicopter. 

 School made sharp course change away from ship and ac- 

 celerated to 4.6 kn. 

 School turned away from ship and accelerated from 2.6 to 



8 4 kn. 

 School moving away from ship at high speed (ca. 10 kn) 



when first sighted from helicopter. 

 School moving away from ship at high speed (8.8 kn) when 



first sighted from helicopter 

 School leaping away from ship when first sighted from 



helicopter 



Figure 4. — Relative motion plot of school 5, showing its 

 apparent motion as seen by a shipboard observer. Small 

 arrows show actual school velocities at various distances. Note 

 heading reversal shown at 1.5 mi. 



represent the actual swimming directions of the 

 school, but rather the resultant of the swimming 

 velocity of the school and the movement of the 

 vessel. The ship's position remains at the center 

 of each diagram, and swimming direction is 

 depicted relative to the ship's heading, which is 

 toward the top of the page. The plots therefore 

 show the apparent motion of the schools as seen 

 by an observer aboard the ship. A break in the 

 relative motion line for a school represents a 

 course change by the ship. 



The relative movement of five schools (schools 

 2, 3, 4, 6, and 7) are depicted in Figure 3 where, 

 for clarity, swimming speed vectors and the 

 times of radar fixes are not included. It is 

 important to realize however, that along each 

 relative motion line the school is generally 

 swimming away from the oncoming ship. We 

 have extrapolated parts of the movements of 

 schools 2 and 3, based upon our observations of 

 their activity. The movement of each of the five 



schools is depicted as though moving relative to 

 the same ship heading (000°). These schools are 

 described in two groups. 



The first group (schools 2, 3, 4, and 6 in Figure 

 3) was initially located between 5 and 7 nmi from 

 the ship. After some initial adjustments in 

 heading, the schools' swimming directions re- 

 mained relatively constant. The resultant paths 

 of the dolphin schools thus veered from the track 

 line at a nearly constant angle after this initial 

 period. Assuming that the schools would remain 

 approximately on the same course and extending 

 their lines of relative movement, it appeared that 

 these schools would have passed no closer than 

 2.4 nmi from the ship, had it remained on the 

 same course. School 4 exhibited additional 

 notable behavior that is not shown in Figure 3. 

 When the school had passed abeam, the ship was 

 turned towards the school. Five minutes later, at 

 a range of about 2.5 nmi, a large section of the 

 school turned and headed toward the ship in a 

 tightly aggregated group. Within a minute this 

 section reversed course again and rejoined the 

 original school. 



The second group (schools 2, 3, and 7 in Figure 

 3) consists of schools that were between 2.6 and 

 3.7 nmi away, either when first sighted (school 7) 

 or after the ship had turned toward the school at 

 the end of an initial tracking period (schools 2 

 and 3). The lower and separated segments of the 

 latter schools' tracks represent the relative 

 movements after the ship had turned. These 

 schools were then within 0.4 nmi of the ship's 

 projected track. Even so schools 2 and 3 

 subsequently came no closer than 1.4 nmi to the 

 ship. School 7, by its initial projected trajectory, 

 would have come no closer than 1.5 nmi, but after 

 the ship turned toward it, its new resultant path 

 would have taken it about 0.7 nmi from the ship. 



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