FISHERY BULLETIN: VOL. 83, NO. 2 



METHODS 



The experiment was designed to observe the 

 efficiency of shipboard survey operations by using 

 a helicopter to track dolphin schools before, dur- 

 ing, and after shipboard detection. This approach 

 was an enhancement of the design employed by Au 

 and Ferryman (1982) which focused only on the 

 behavior of the dolphins. A simulated survey op- 

 eration was included in the experiment for the 

 following reasons: 



1) It was not reasonable to assume that move- 

 ment of a dolphin school and the probability 

 of detecting it are unrelated (i.e., it may be 

 easier to see a school in full flight than one at 

 rest). Therefore, associated data on move- 

 ment and shipboard detection were collected 

 for each school. 



2) It was necessary to separate random move- 

 ment from directed movement toward or 

 away from the survey vessel. To do so unam- 

 biguously, the ship could not be directed to- 

 ward a school detected by the helicopter, but 

 rather had to continue searching along a 

 predetermined transect. 



were tracked for about an hour's time until one of 

 three events occurred: 1) the school passed 

 abeam of the ship; 2) the school passed beyond the 

 visual range of shipboard observers; or 3) the aer- 

 ial observers lost sight of the school and had to 

 terminate the track prematurely; in all of the 

 latter cases the presence of the animals was 

 obscured by deteriorating sea state. 



During a track, the helicopter was positioned 

 over the school at a minimum altitude of 1,200 ft 

 (370 m); the radar range and bearing to the 

 helicopter were determined from the approaching 

 survey vessel about every 4 min (an interval suffi- 

 cient to record the appropriate navigational data 

 and still provide continuity in the track). A tran- 

 sponder, mounted on the aircraft, facilitated accu- 

 rate radar measurements. In addition, OMEGA 

 navigation positions were recorded from dual sys- 

 tems aboard the helicopter and the ship. As the 

 track progressed, field notes were taken on visual 

 observations of school behavior and associated 

 birds and fish. The tracking altitude appeared to 



SHIP TRANSECT 



t 



From the experience gained on the 1982 survey 

 (Holt 1983), we expected 80% of the sighting cues 

 to be within 3 nmi of the transect line and <5 nmi 

 ahead of the vessel. Furthermore, the Au and Fer- 

 ryman observations on eight schools suggested 

 that dolphins may react to a ship 6 nmi away. With 

 these considerations and prior experience in mind, 

 the following field procedure was employed. 



The ship proceeded at 12 kn in a direction 

 selected so as to minimize glare from the sea sur- 

 face. Two observers maintained constant watch 

 through 25 power binoculars, mounted on the port 

 and starboard sides of the flying bridge (11m above 

 the water); search patterns extended from the bow 

 to the beam of the ship on each side. Records were 

 kept of searching effort and sighting details. With 

 the exception of selecting the transect direction, 

 these are the same methods employed during pre- 

 vious dolphin surveys (e.g.. Holt and Fowers 1982). 

 The helicopter searched a distance of 8 to 12 nmi 

 ahead of the ship and 2 nmi to either side of the 

 transect line, at right angles to the direction of the 

 ship's travel (Fig. 1). Search altitude was 1,200 ft 

 and speed was 60 kn. When a school was sighted by 

 the helicopter, shipboard radar tracking began. 

 The observers on the flying bridge were not aware 

 of a track in progress until its termination. Schools 



I HELICOPTE R PATH 



j-2 nm.-J 

 '8-12 



nm. 



SHIP 



Figure l. — Port and starboard search patterns (shaded areas) 

 and path of helicopter (sohd Hne) during transect (dashed line) 

 surveys for dolphins. 



188 



