NOAA Technical Memorandum NMFS 

FEBRUARY 1983 

REPORT OF PORPOISE EXPERIMENT TESTING 

DETECTION OF ON-TRACK SCHOOLS (PET DOTS), 

MARCH 7-APRIL 5, 1981 

Rennie S. Holt 

NOAA-TM-NMFS-SWFC-27 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

Southwest Fisheries Center 
NOAA Technical Memorandum NMFS 

The National Oceanic and Atmospheric Administration (NOAA), organized in 1970, has evolved 

into an agency which establishes national policies an manages and conserves our oceanic, coastal, and 

atmospheric resources. An organizational element within NOAA, the Office of Fisheries is responsible for fisheries policy and the direction of the National Marine Fisheries Service (NMFS). 

In addition to its formal publications, the NMFS uses the NOAA Technical Memorandum series to 

issue informal scientific and technical publications when complete formal review and editorial processing are not appropriate or feasible. Documents within this series, however, reflect sound professional 

work and may be referenced in the formal scientific and technical literature. 
COEITE N TS 

Page 

INTRODUCTION................... ..................................... 

OBJECTIVES... ....................................................... 

V AR I AB L E S ME AS U RED 

Sea State ....................................................... Sun Glare............ ........................................... Observer Performance........... ................................. 

STUDY AREA AND ITINERARY 

Area of Operation ............................................... Flight Schedule.. ............................................... 

PERSONNEL 

Scientific Party ................................................ Flight Crew.................................................,... 

1 

1 

2 

2 

3 

3 

3 

4 

4 

EQ U I PME N T 

Aircraft........................................................ 4 

Navigation Syste ................................................ 5 

Cameras............................ ............................. 5 

Binoculars ...................................................... 5 

Dye Markers........ ............................................. 5 

C1ock............................... ............................ 6 

DUTY STATIONS....................................................... 6 

OBSERVER TEAMS AND ROTATIOI~............................... .......... 7 

PROCEDURES 

Flight Procedures............................................... 7 

Search Procedures............................................... 8 

RESULTS............................................................. 10 

LITERATURE CITED.............................. ...................... 12 

APPENDIX I......................................................... 76 

APPENDIX II......................................................... 79 

i 
LIST OF TABLES 

Tab1 e Page 

1 Sea state conditions measured by the Beaufort 

scale (from Bowditch, 1966) ............................. 13 

2 Searching effort, sun position, Beaufort number, 

and observer positions during each leg of flights 

1 through 16. Observer and Beaufort number codes 

defined in text. Cloudy conditions denoted by '0' 

horizontal and vertical posi ti on. Zero Val ue for 

'speed KMIHR' denotes data not recorded ................. 14 

3 Searching effort, sun position, Beaufort number, and 

observer positions during each leg of flights 2 

through 16 occurring outside the study area. 

and Beaufort number codes defined in text. 

conditions denoted by '0' horizontal and vertical sun 

position. Zero value for 'speed KM/HR' denotes data not 

recorded..... ........................................... 28 

Observer 

Cloudy 

4 Dolphin schools, sun position, Beaufort number, 

observer detecting school and perpendicular distance, 

summarized by species codes, recorded duri ng f 1 i ghts 

1 through 16. School size estimates of zero denotes 

data not recorded. 

effort occurring outside the study area denoted 

by '*I .................................................. 31 

Schools detected during legs of 

ii 
Figure 

LIST OF FIGURES 

Page 

Vertical (top) and horizontal (bottom) sun 

positions. 

horizontal and vertical position ..................... 57 

Tracklines flown from the airplane during flights 

1 through 16 ......................................... 58 

Aerial survey transect record........................... 59 

Aerial survey sighting record........................... 60 

Tracklines flown in the study area during flight 2. 

61 

Tracklines flown in the study area during flight 3. 

62 

Tracklines flown in the study area during flight 4. 

63 

Tracklines flown in the study area during flight 5. 

64 

Tracklines flown in the study area during flight 6. 

65 

Tracklines flown in the study area during flight 7. 

66 

Tracklines flown in the study area during flight 8. 

67 

Tracklines flown in the study area during flight 9. 

68 

Tracklines flown in the study area during flight 10. 

69 

Tracklines flown in the study area during flight 11, 

70 

Tracklines flown in the study area during flight 12. 

71 

Tracklines flown in the study area during flight 13. 

72 

Tracklines flown in the study area during flight 14. 

73 

Tracklines flown in the study area during flight 15. 

74 

Tracklines flown in the study area during flight 16. 

75 

Trackl ines surveyed with good sea state conditions 

77 

Trackl i nes surveyed with poor sea state conditions 

78 

C1 oudy conditions denoted by zero 

Study area defined in text........................... 

Study area defined in text........................... 

Study area defined in text........................... 

Study area defined in text........................... 

Study area defined in text........................... 

Study area defined in text........................... 

Study area defined in text........................... 

Study area defined in text........................... 

Study area defined in text ........................... 

Study area defined in text........................... 

Study area defined in text........................... 

Study area defined in text........................... 

Study area defined in text........................... 

Study area defined in text.. ......................... 

Study area defined in text........................... 

(Beauforts 0-2) during Flights 2-16 .................. 

(Beauforts 3-6) during Flights 2-16 .................. 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

AI -1 

AI -2 

iii 
REPORT OF PORPOISE EXPERIMENT TESTING DETECTION 

OF ON-TRACK SCHOOLS (PET DOTS), MARCH 7-APRIL 5, 1981 

Rennie S. Hol t 

Southwest Fisheries Center 

National Marine Fisheries Service, NOAA 

La Jolla, California 92038 

INTRODUCTION 

The National Marine Fisheries Service (NMFS) has the responsibility of 

assessing the status of the porpoise stocks which are affected by the Eastern 

Tropical Pacific tuna purse seine fishery. Stock assessments rely on 

estimates of the present population size of the stocks. Population abundance 

estimates were made in 1975 (Smith 1975l, 1981) and 1979 (Holt and Powers, 

1982) using line transect methods. I conducted an experimental aerial survey 

in 1980 off the coast of Costa Rica to test several of the assumptions made in 

the use of line transect theory for estimating porpoise abundance with aerial 

survey data. This paper describes the experimental procedures and the data 

obtained in this survey. 

OBJ ECTI VES 

The primary objective of the experiment was to examine the effect of 

environmental factors and observer performance on line transect methods used 

for estimating density of dolphin schools. Environmental factors investigated 

were sea state and sun glare. Observer performance was examined with 

experienced and i nexperi enced teams of observers. A secondary objective was 

to evaluate the use of aerial photographies for measuring dolphin lengths, 

determi ni ng speci es composition of school s, and compari ng the precision of 

observer estimates of dolphin school size. 

Specific requirements to accomplish the objectives of the survey were: 

1. Use of a slow, low flying aircraft with a configuration permitting 

unobstructed views to the front, downward, and to both sides of the 

pl ane. 

2. Fly track1 ines so that similar fl ights were made under a range of 

sea state conditions and with different orientations to the sun. 

lSmith, T. D. 1975. 

(Stenella) in the eastern tropical Pacific Ocean. Southwest Fisheries Center 

Adminstrative Report No. LJ-75-67. La Jolla, CA 88 pp. 

Estimates of sizes of two populations of porpoise 
2 

3. 

4. 

5. 

6. 

7. 

Sea 

Insure that observers with aerial surveying experience and those 

without experience had equal opportunity to search for schools under 

a1 1 environmental conditions. 

Search for dolphin schools using methods compatible with line 

transect theory and estimate, either visually or using a 

navigational system, the perpendicular distance of each school from 

the track1 i ne. 

When conditions permitted, obtain vertical 1.97 cm and 0.89 cm 

format photographs of dolphin schools for enumeration of individuals 

and for studying school composi tion. 

When necessary, leave the trackline and circle dolphin schools to: 

(a) estimate the number of individuals, (b) identify the species, 

and (c) record swimming patterns, school configuration and other 

behavi oral aspects . 

Have two observers in the bow such that one monitors the activities 

of the other to determine if schools are missed and not recorded. 

VARIABLES MEASURED 

Sea State 

state was measured usins the Beaufort scale (Table 1) which ranged 

from Beaufort 0 (very calm sea;) to Beaufort 6 (rough seas). Sea state 

conditions were recorded at the time searching began or was resumed, at the 

time of a dolphin sighting and whenever sea state conditions changed. 

Sun Glare 

Sun glare effects are dependent not only upon the sun's horizontal 

position but a1 so its vertical position. Horizontal sun position was recorded 

using the positions of a clock face with 12 o'clock directly ahead. Vertical 

position was recorded as 12, 1, 2, or 3 with 12 directly overhead and 3 on the 

horizon (Figure 1). Sun positions were not recorded during cloudy 

conditions. Sun glare conditions were recorded at the time searching began or 

was resumed, at the time of a sighting and whenever sun position changed. 

During previous aerial surveys (Holt and Powers, 19821, the bow observer 

was instructed to terminate the searching effort if he felt that all animals 

(schools with >14 animals) on the trackline could not be detected with 

probability of one. This may have occurred due to rain, darkness, very rough 

sea states or more frequently the presence of direct sun glare on the 

trackline. During this experiment we continued to search during all sun 

positions in order to define a range of conditions where all schools on the 

trackline could be detected. 

Y 
3 

Observer Performance 

The critical assumption that all schools on the trackline are detected 

may be affected by the ability of individual observers to detect schools. 

Experience in detecting animals from the air may be critical. Therefore, in 

this experiment data for observers with previous aerial survey experience and 

those without were collected. In addition, a bow monitor provided a direct 

visual check of the bow observer's performance. 

STUDY AREA AND ITINERARY 

Area of Operation 

The aircraft operated along the Pacific coast near Liberia, Costa Rica. 

Flights occurred in a coastal band extending seaward for approximately 55.5 km 

and parallel to the coast for approximately 111 km (Figure 2). The 

experimental design required the study area be sampled under a1 1 environmental 

conditions. The area defined was offshore the coastline from 9'41' to 10'40'N 

latitude and from 85'20' to 86'21'W longitude. This area was selected by 

examining the location of effort encountered under the various sea state 

conditions. Furthermore, the location of the western longitudinal boundary 

was selected to maximize the chance of enough survey effort in the area while 

insuring all experimental factors were spatially distributed and to reduce the 

inclusion of bias owing to onshore-to-offshore density gradients (Appendix I). 

F1 i ght Schedule 

The survey was scheduled to begin January 2, 1981; however, because of 

mechanical and logistical problems, the first survey flight did not occur 

until March 7, 1981. The plane was ferried from its home base in Naples, 

Florida to San Jose, Costa Rica between February 18-22, 1981, and to the study 

base at Liberia, Costa Rica on March 1, 1981. Survey flights were conducted 

between March 7 and April 5, 1981 out of Liberia. The plane was ferried back 

to Naples between April 7-9, 1981. Survey flight schedules were: 

Flight Departure Return F1 ight Length 

number Date (local time) (local time) (hours:minutes) 

1 3/7 1455 

2 3/9 1400 

3 3/10 0750 

4 3/11 0830 

1314 

5 3/12 0637 

1252 

6 3/13 0632 

1312 

1720 

1732 

1144 

1200 

1708 

1016 

1714 

1105 

1655 

2:25 

3:32 

3:54 

3: 30 

3:54 

3:39 

4:22 

4: 33 

3:43 
4 

F1 ight Departure Return Flight Length 

number Date (local time) (local time) ( h ou r s : in i n u te s ) 

7 

8 

9 

10 

11 

12 

13 

13 

14 

15 

16 

3/15 

3/16 

3/17 

3/19 

3/20 

3/21 

3/22 

4/ 1 

4/3 

4/4 

4/5 

0651 

1335 

0637 

0637 

0646 

1438 

0854 

0620 

1338 

06 14 

0657 

1358 

618 

1445 

06 14 

1409 

1113 

1726 

1118 

1245 

1207 

1720 

1146 

1108 

1651 

1029 

0926 

1742 

1045 

1800 

1050 

1710 

4:22 

3:51 

4:41 

6:08 

5: 21 

2:42 

2:52 

4:48 

3: 13 

4: 13 

2:29 

3:44 

4: 27 

3: 15 

4:36 

3:Ol 

PERSONNEL 

Scientific Party 

Rennie Holt, Chief Scientist, NMFS 

William Brinkerhoff, NMFS 

Larry Hansen, NMFS 

Mark Lowry, NMFS 

Frank Ralston, NMFS 

Will iam Walker, Los Angeles Natural History Museum (contractor) 

Flight Crew 

John Olson, Chief Pilot (Flights 1-13) 

Timothy Flynn, Chief Pilot (Flights 14-16) 

Robert DeRosa, Co-Pilot 

EQUIPMENT 

Aircraft 

A Beech , AT11-A modi f i ed, two-engi ne, ex-mi 1 i tary bornbardi er trainer 

aircraft, owned and operated by Aero-Marine Surveys, Inc., Groton, Connecticut 

was used in the survey. Reasons for selecting this aircraft were: 

1. Flying speed - The plane was capable of flying a tninimttm of 185-278 

km/hr depending on prevailing winds. 

aerial surveys indicates flights should be flown in this range to 

ensure detection of school s on the track1 i ne. 

Experience with previous 
5 

2. 

3. 

4. 

5. 

6. 

Observation areas - As a bombardier trainer, the nose of the 

ai rpl ane was made of p l e x i gl ass , a1 1 owing unobstructed forward and 

downward visibility. 

installed in the rear of the plane. 

allowed unobstructed vertical and aft view with less than 185 m 

from the track1 i ne. 

approximately 555 m was partially obstructed by the wings of the 

pl ane. 

Modified left and right waist windows were 

Forward vi si bi 1 i ty at di stances greater than 

These windows were 41x58 cm and 

Range - Fully loaded and in good flying conditions the plane was 

capable of flying at least 1159 km. 

Safety - The plane could fly on one engine if necessary. 

Cost - The hourly contract rate allowed a sufficient number of 

flights to obtain the needed sample sizes. Additionally, the plane 

was offered at the lowest price in the competitive bidding process. 

Experience of contractor - Aero-Marine Surveys had considerable 

experience conducting surveys of this type. 

Navi ga ti on Sy s tem 

An Omega Navigation System (ONS) was used throughout the survey. The 

system was used by the scientists to obtain geographic position, ground speed, 

and perpendicular distance of a school from the trackline. Data could be 

"frozen" in the display mode for subsequent transferring to data sheets. 

Cameras 

Three different format-size cameras were used to photograph dolphin 

schools and document the survey. These were a KA-62A (1.97 cm) format aerial 

reconnaissance camera, four 70 rnm (0.89 cm format) Hasselblad cameras, and a 

Nikon 35 mm camera. 

Binoculars 

Two types of binoculars were used. One, SWIFT Admiral Mark I, Model No. 

751 (10x50 power) glasses, was used primarily to inspect possible targets seen 

with the unaided eye at long distances from the plane and the other, Minolta 

Celtic (7x35 power) wide angle binoculars, was used in making species 

i den ti f i ca ti ons . 

Dye Markers 

A mixture of eosin, powered aluminum and small gravel enclosed in a paper 

bag was dropped from the plane as near a school as possible to aid in 

returning to the location of the school. 
G 

Clock 

A digital Casio battery operated clock was used to record time of 

sightings and positions. The clock displayed hours and minutes only. 

Consequently, calculations of ground speed for some legs of effort where few 

ki 1 oineters were searched were imprecise. 

DUTY STATIONS 

Six duty stations were used during the survey, with observers rotating 

sequentially through all stations. 

1. Bow: The bow observer sat in the plexiglass nose. His major 

responsibility was to detect all schools in a path approximately 

185 m wide directly beneath the aircraft. 

plane over a school when in a circling mode. 

He usually directed the 

2. Recorder: The recorder sat directly behind the pilots where he could 

visually monitor the ONS readout. He did not have access to the ONS 

controls, and had to request the pilots to display specific data 

elements in the readout unit. His duties were to take transect data 

at regul ar interval s and make notes of any perti nent informati on 

transmitted to him via the Internal Comniunication System (ICs). At 

times of sightings he was responsible for immediately recording the 

plane's position, time, and perpendicular distance of the school 

from the trackline. 

sighting forms (Figures 3 and 4) were recorded while the sighted 

school was being observed. Observer school size estimates were 

generally not given over the ICs. 

Other data required by the transect and 

3. Left Waist: The port side observer sat on a cushion in the extreme 

The viewing window was located in the rear of 

aft of the cabin and observed an area from the edge of the plane 

outboard to a varied 1 imi t set pritnari ly by envi ronrnental conditions 

and plane a1 ti tude. 

the plane so that the observer could see downward slightly under the 

plane, for observation of part of the trackline. 

4. Bow Monitor: The bow monitor sat beside the bow observer in the 

plexiglass nose of the aircraft. 

visual check of the ability of the bow observer to detect schools 

directly beneath the airplane. 

indicating the presence of a school until it was obvious that the 

bow observer had failed to detect its presence i.e. the plane had 

completely overflown the school wi thout its detection. 

His major duty was to serve as a 

The bow monitor refrained from 

5. Right Waist: The starboard observer sat on a cushion adjacent the 

port observer but on the starboard side of the aircraft. His duties 

were identical to the left waist observer except on the opposite 

side of the aircraft. 

6. Off: The last station was a nonduty rest position. 
7 

OBSERVER TEAMS AND ROTATION 

Observers changed positions either when the plane reversed directions to 

survey in the opposite direction or after 45-55 minutes if the plane was 

following tracklines that zig-zagged across the study area. As a result of 

the rotational system observers were effectively partitioned into two teams, 

each with three members. The members of the "experienced" team had 

participated in previous aerial surveys that used line transect methods, while 

the members of the "inexperienced" team had not participated in aerial surveys 

of any type and were not familiar with line transect methods except as 

instructed during the presurvey training. Experienced observers were assigned 

number codes 8, 10 and 11 while inexperienced observer codes were 12, 13 and 

14. Each team represented an independent effort in that members of a team 

always occupied the observational positions (bow observer, left and right 

waist) at the same time, and alternated observing with members of the other 

team. 

The experienced and inexperienced teams a1 ternated occupying the 

observational positions at the beginning of each flight. The bow monitor was 

a member of the opposing team. A die was rolled to determine specific 

starting duty stations within each team. Positions were assigned so that each 

observer had approximately equal access to each starting position. 

Training for the study included flights aboard U.S. Coast Guard 

helicopters near San Diego, emphasizing (1) sighting cues used to detect 

marine mammals, (2) methods to estimate school sizes, (3) use of the Beaufort 

scale, and (4) familiarization with each element collected on the data forms. 

PROCEDURES 

F1 ight Procedures 

One day's searching effort was considered as a single flight, although 

the plane may have made a refueling stop. Ideally a typical day's activities 

consisted of: departing the aerodrome between 0600-0630, a 10-minute ferry to 

the study site, surveying until 1130, returning to airport and refueling, 

departing around 1330, surveying until 1700 and finally returning to the 

aerodrome to refuel for the next day's flight. This schedule was modified 

frequently due to mechanical and logistical problems so that only the morning 

or afternoon segment was completed. Because of delays encountered prior to 

the beginning of the survey flights, a 4-day flight schedule was attempted. 

The first and third days' flights included morning and afternoon segments, the 

second day's flight included only a morning segment, and the fourth day was an 

off day. This schedule however could not be maintained due to mechanical and 

logistical emergencies. In practice, flights were generally completed when 

the plane and crew were available. A summary of events that contributed to 

flight schedule changes is given in Appendix 11. 

Once on a survey track, the pilots followed a predetermined line and 

maintained an altitude of 274 m. The aircraft's ground speed was generally 

maintained between 185 and 278 km/hr dependent upon wind speed and 
8 

direction. The plane's course usually was not altered to avoid rain squalls. 

Tracklines were oriented to provide a range of orientations of the plane 

to the sun. Generally lines were placed parallel to the coast in a northsouth and northwest-southeast directions (Figure 2). Lines were a1 so surveyed 

which criss-crossed the study area to obtain desired sun orientations. The 

same trackline may have been flown on more than one occasion. The location of 

the first trackline flown each day was varied with distance from shore. 

Search Procedures 

In general , searching procedures used to detect dol phin school s foll owed 

those used in the NMFS 1979 aerial survey (Jackson, 19792) with a major 

difference that the search mode was not terminated under adverse conditions. 

The search mode of each survey flight began when the plane was on the 

trackline. On a cue from the pilot, time and position were recorded and the 

observers began scanning the sea surface for signs of dolphins. Sighting cues 

used to locate the dolphins differed depending on the sea state, sun position, 

size of the school, behavior of the dolphins, and distance of the school from 

the aircraft. 

The distance from the plane at which a school could be observed 

decreased as the sea state increased. For example, with calm seas, Seaufort 

two or less, various sea surface patterns could be distinguished up to several 

miles away from the aircraft. These patterns, referred to as "scars," would 

then be scrutinized with binoculars to determine the presence of dolphins. 

Under the same conditions, but closer to the plane, surface disturbances 

and/or the dolphins themselves were often the sighting cues. As sea 

conditions worsened, with larger swells and more white caps, scars and other 

surface disturbances became more difficult to detect. Such changes 

necessitated that the observer concentrate his efforts closer to the 

aircraft. Under adverse sea conditions, Beaufort five or higher, the animal 

itself was usually the only discernible sign. In these situations, all 

searching was done close in to the airplane. Bird activity was also used as a 

sighting cue during all sea states. 

All observers, including the "off" observer if he desired, were in 

constant communication with each other and the pilots via the ICs. Throughout 

each survey flight, the recorder maintained a Transect Record (Figure 3) of 

the flight, leg number, date, altitude, ground speed (indicated on the ONS), 

and the code numbers of personnel at each of the observer stations. Sea state 

and sun position were also noted after consultation with the observers. A new 

transect record or leg was started at each rotation of observers, when the 

airplane made a major course or altitude change, or when environmental 

conditions changed, e.g., a change in Beaufort or sun position. Geographic 

2Jackson, T. D. 1979. Trip report: porpoise population aerial survey of the 

eastern tropical Pacific Ocean, January 22-April 25, 1979, Southwest Fisheries 

Center Administrative Report. LJ-80-1, La Jolla, CA 74 pp. 
9 

positions and local times were recorded at the beginning and end of each leg 

and at frequent intervals (transect checks) throughout the leg. Local time 

was subsequently converted to Greenwich Mean Time. Posi ti ons were a1 so 

recorded for each sighting and when the aircraft diverted or returned to the 

trackline. "Search" or "no search'' modes were noted for each geographic 

position and "sighting record numbers" were referenced to specific positions 

where a sighting occurred. 

When a sighting was announced, the recorder immediately logged the time 

and position, and assigned a sequential sighting number. Concurrently, the 

person making the sighting determined if the plane should be diverted from 

track to investigate. The plane generally did not divert if (a) the school 

consisted solely of large whales, (b) a suspected cue was detected at a 

perpendicular distance substantially greater than 1.85 km, (c) the school size 

was obviously less than 15 animals, or (d) for schools with more than 15 

animals, environmental conditions were unsuitable for photography. If the 

observer determined that a sighting was made but decided not to divert the 

plane for further observations, he instructed the pilot to continue on 

track. He then relayed his information concerning the sighting to the 

recorder who filled out a Sighting Record (Figure 4) data sheet. Observer 

search effort continued if the airplane was not diverted. 

If the observer decided to divert the plane, he asked the pilot to turn 

left or right so he could continue observing the school as the plane 

circled. At the same time, he also instructed the recorder to note the "cross 

track'' distance if he felt an accurate reading could be obtained. 

If condi ti ons were sui tab1 e for aeri a1 photography, the observer 

requested a photographic run. The pilots then positioned the plane between 

the sun and the school, so that the approach was made with the sun on the 

aircraft's tail, a pattern found most effective in previous aerial surveys. 

The observer also instructed the pilots to reduce airspeed to approximately 

185 km/hr while maintaining 274 m. Normally, the bow observer, having 

visually located the school while the plane circled, directed the pilots over 

the school during a photographic pass. From the bow position, he either fired 

the cameras or commanded another observer to start and stop the picture 

series. When the plane was directly over the school, the recorder was 

instructed to obtain another cross-track distance and, if possible, a 

geographic position. The perpendicul ar distance of the school from the 

aircraft was subsequently calculated. 

Following the photographic run(s), the approach pattern was changed 

slightly to allow optimum observation for the observers to estimate school 

size. On these passes, still at 274 m, the plane was positioned so that the 

dolphin school was situated within 185 or 370 m of the plane and on the side 

opposite the sun. As the aircraft approached the school , the pilot, usually 

directed by the bow observer, dipped the wing to give the observers a near 

vertical view of the school with minimum glare. All available observers made 

independent estimates of school size. Using this same circling pattern, 

species identification was attempted. One observer, usually Mr. Walker, the 

marine mammal identification specialist, viewed the dolphins through wide 

angl e bi nocul ars whi 1 e the rernai ni ng observers 1 ooked wi th the1 r unai ded 
10 

eye. Between 

took place to 

cont nued unt 

(usual ly less 

each pass, discussions on noted identification characteristics 

assist in determining the species. Circling in this manner 

1 a positive identification was made or time constraints 

.han 10 minutes) necessitated returning to the trackl ine. 

If conditions were not suitable for photography, the circling procedure 

was abbreviated. An attempt was made to estimate school size and, if 

possible, to determine species identification in one pass. If it was apparent 

that school size was greater than 14, the plane returned to track. 

Li ne transect methods require determining perpendicular distances of 

objects, recorded as points, frorn the trackline (Burnham et al., 1980). 

Dolphin school configurations are not points but range from tight compact 

clusters to loose aggregations. In theory, the mid-point of the configuration 

shoul d be uti 1 i zed to determi ne perpendicul ar distance; however , given the 

speed of the aircraft and the spatial distribution of the animals, this was 

not practical. Instead, the perpendicular distance for a school was estimated 

by determining the distance of the initial sighting cue (i.e. first animal(s) 

detected) to the trackl i ne. 

The applied definition of a "school" affects the number of schools 

recorded. A group of dolphins spatially distributed over a small area in a 

loose aggregation could be viewed as one large school or several smaller 

independent schools. The 

decision was somewhat subjective, but we attempted to be consistent over all 

experimental conditions. 

We tended to view those aggregations as one school. 

As the aircraft returned to track to resume searching, each observer made 

notes, in a personal notebook, of estimated school size (best-high-low) and 

species composition. School size was not discussed over the ICs if more than 

one observer made an estimate. Search effort resumed when the plane was at 

the searching altitude and back on track. 

On occasion, when sightings occurred in rapid succession, the recorder 

asked each observer to record notes in his own log book concerning the 

sighting. Sighting numbers were supplied over the ICs to insure that data 

rJere coded accurately. 

RESULTS 

The primary objective of collecting data to allow comparison of sighting 

survey results under various sea state and sun angle conditions was 

accomplished with 373 sightings of marine mammals made while surveying 13,157 

km in 16 flights. The tracklines searched for all flights (Figure 2) were in 

the area from 8"N to 11"N latitude, and from 85"W to 88"W longitude. Within 

the study area, 252 marine mammal sightings, which met all selection criteria, 

were made while surveying 10,712 km on 15 flights (Figures 5-19). 

Data collected on each leg of effort for all flights, including the date, 

altitude, indicated ground speed, location of each observer, sun position, sea 
11 

state, number of sightings of schools of marine mammals, km covered, and mean 

km/hr for each leg are given in Table 2. Data collected outside the study 

area are presented in Table 3. The "speed km/hr" was ground speed recorded 

from the ONS at the time each leg began while ''mean km/hr in leg" was averaged 

ground speed calculated by dividing distances searched in a leg, determined 

from starting and endi ng geographi c posi ti ons , by el apsed time i n search 

mode. The latter is a better indicator of speed. 

The details for each of the marine mammal sightings classified by species 

groups are given in Table 4. Included are the flight and leg, date, sun 

position, Beaufort number, observer making the sighting, perpendicular 

distance to the sighting, geographic position, and the school size. Most of 

the schools were not identified to species, as discussed previously. Eight of 

the 373 marine mammal schools recorded during the survey were identified as 

including two species (mixed schools) and, therefore, are presented twice in 

the species lists and summary tables (i.e. total schools in Table 4 equal 

381). Sighting which occurred outside the study area are denoted by an 

asterisk in Table 4. 

The requirements of the survey, listed on page 1, necessary to accomplish 

the objectives were met to various degrees. Requirements 2, 3, 4 and 7 were 

completed adequately: various sea states and sun orientations were 

encountered; experienced and inexperienced observer teains remained intact 

throughout the experiment; perpendicular distances were estimated for 

virtually all sightings and a bow monitor was present on all legs of all 

flights. During the survey, two schools were detected by the bow monitor 

which were not detected by the bow observer. These were schools 30 and 210 

(Table 4). Requirement for use of a slow flying aircraft with unobstructed 

forward and downward views was partially met. The aircraft's speed was 

satisfactory; however, the view forward of the aircraft from the side ports 

was restricted by the wings. This reduced the time a school was available for 

detection before it was overflown. Requirement 5, aerial photography, was not 

accomplished due to very high sea states and minimal off-track circling. 

Requirement 6 was met, except that the procedure to minimize off-track 

circling resulted in a large number of the schools recorded as unidentified 

dolphins (Table 4). 

The data presented here will allow evaluation of line transect density 

estimation methods under different sighting conditions and for observer 

effects. Detailed analyses of the data are under way. 
12 

LITERATURE CITED 

Bowdi tch , N. 1966. American practical navi gator, an epi tome of navi gati on. 

U. S. Naval Oceanographic Office. H. 0. Pub. No. 9. Washington, DC. 1524 

PP 

Burnham, K. P., D. R. Anderson and J. L. Laake. 1980. Estimation of density 

for line transect sampling of biological populations. --- J. Wildl. Manag. 

Monographs No. 72, 220 pp. 

Holt, R. S., and J. E. Powers. 1982. Abundance estimation of dolphin stocks 

involved in the eastern tropical Pacific yellowfin tuna fishery 

determined froin aeri a1 and ship surveys. NOAA TM-NMFS-SWFC-23, 95 pp. 

Smith, T. D. 1981. Line transect techniques for estimating density of 

porpoise schools. --- J. Wildl. Manag. 45(3):650-647. 
13 

Table 1. Sea state conditions measured by the Beaufort scale 

(from Bowdi tch, 1966). 

Wind 

force 

(Beau- Descri pfort) Knots tive 

0- 1 

1- 3 

4- 6 

7-10 

11-16 

17-21 

22-27 

28-33 

Calm 

Light air 

Light 

breeze 

Gent1 e 

breeze 

Mod era t e 

breeze 

Fresh 

breeze 

Strong 

breeze 

Near gal e 

Sea conditions 

Sea smooth and mi rror-1 i ke. 

Scal e-1 i ke ri ppl es without foam crests. 

Small short wavelets; crests have a 

glassy appearance and do not break. 

Large wavelets; some crests begin to 

break; foam of glassy appearance. 

Occasional white foam crests. 

Small waves , becomi ng 1 onger; fai rly 

frequent white foam crests. 

Moderate waves , taking a more pronounced 

long form; many white foam crests; there 

may be some spray. 

Large waves begin to form; white foam 

crests are more extensive everywhere; 

there may be some spray. 

Sea heaps up and white foam from breaking 

waves begins to be blown in streaks along 

the direction of the wind; spindrift 

begins. 

Probable 

wave 

height 

in ft. 

1/4 

1/2 

2 

4 

6 

10 

14 
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=3 
57 

12 

3 3 

12 

6 

Figure 1. Vertical (top) and horizontal (bottom) sun positions. Cloudy conditions denoted by zero horizontal and vertical posi ti on. 
58 

12O 

11' 

2 

0 

w 

I5 loo 

F 

a 

-1 

9O 

8O 

. 

1111111 

I 11111 

I 11111 

I ,,I 

85O 84O a70 86O 8a0 

LONGITUDE O W. 

Figure 2. Tracklines flown from the airplane during flights 1 through 16. 
59 

ALTITUDE DATF BLAN'( FLIGHT LEG 

NO NO YR I MO I DAY IFFET 

I I I I I Ill 

AERIAL SURVEY TRANSECT RECORD 

GROUND 

SPEED 

IKNOTSi 

I I_ 

FLIGHT LEG DATE 

FROM TO 

LEFT RIGHT RECORDBO6 I BLANK , hA1ST I WAIST I ER 

I I I I 

BEAUFORT 

HORIZ I VERT NO 

I I 

I SUN POSITION I OBSERVER CODES 

LATITUDE 

41 41 45 48 49 53 36 38 

REASON 

FOR 

POSITION 

I, Beg." Leg 1. Track Check 

3. D~vcrf 

4. Ovcrrchool 

5. Return 

6 End Leg SEARCHING 

55 M 58 

IiUM FQRM No. 9E-17.L 1/74 

Figure 3. Aerial survey transect record. 
60 

SIGHTING 

NO. 

AERIAL SURVEY SIGHTING RECORD 

FLIGHT LEG hS LEFT RIGHT RECORDNO. NO. NO. YR Mo DAY BOW WAIST WAIST ER 

II I I I I I I I- 1 4 6 8 9 II 13 15 17 19 21 

70 mm CAMERA 

ROLL NO 1st. FRAME -AS1 FRAME 

CLOCK OF POSITION SUNd 1 1 ~UFORT 

VERT ?F t TENTHS) wnw 

23 25 27 30 31 

9" CAMERA 35 mm CAMERA 

ROLL NO 1st FRAME LASTFRAME POLL NO 1st FRAME LASTFRAME 

DISTANCE 

1. GNS 

2. ESTIMATED 

3. INCLINOMETER 

II I1 I1 II II It 

33 36 

II I1 II 

m 

OBSERVER CODES 

1. BARHAM 

2. CHARTER 

3. COE 

4. JACKSON 

5. LEATHERWOOD 

6. OLIVER 

7. POWERS 

8. WALKER 

9. PERRYMAN 

10. HOLT 

1 47 

SCHOOL SIZE ESTIMATES 1 ::E, , i YEST, i ,'lJ:T, 1 , %:,E 1 NAME 

48 M 54 58 62 65 , SIGHTING CARD 

(

19 

(3))J 

24 26 30 34 38 41 

II I I I I I I I I l(4)lJ 43 45 49 53 57 M) 

I 'I"' I I I I 1 

76 79 

PORPOISE 0 BIRDS c] TUNA 0 1 45 7 11 I5 19 20 21 

~ 

45 48 51 22 26 I 27 33 36 39 42 

26-SCHOOL MODE AT 

TIME OF T' PHOTOS 

I. TRAVELING 

2. RESTING 

3. FEEDING 

Y WAS PLANE IN SEARCH MODE h Y 

71) 

55 58 61 

Figure 4. Aerial survey sighting record. 
61 

lOO40' 

1 OOOO' 

LONGITUDE O W. 

Figure 5. Tracklines flown in the study area during flight 2. Study area 

defined in text. 
62 

10'40 

z 

0 

1 O00O' 

COSTA RlCA 

LONGITUDE O W. 

Figure 6. Tracklines flown in the study area during flight 3. Study area 

defined in text. 
63 

1 0 '40' 

i 

0 

1 OOOO' 

E 

COSTA RlCA 

LONGITUDE O W. 

Figure 7. Tracklines flown in the study area during flight 4. Study area 

defined in text. 
64 

10'40 

i 

0 

w 

3 

ln 

t 

a 

.J 

1 0'00 

n 

86 85'20' 

LONGITUDE O W. 

COSTA RlCA 

Figure 8. Tracklines flown in the study area during flight 5. Study area 

defined in text. 
65 

10'40' 

i 

0 

1 OOOO' 

86'00' 

LONGITUDE O W. 

Figure 9. Tracklines flown in the study area during flight 6. Study area 

defined in text. 

COSTA RlCA 

85O20' 
66 

i 

0 

1 OOOO 

10°40’ 

, 

COSTA RlCA 

LONGITUDE O W. 

Figure 10. Tracklines flown in the study area during flight 7. 

defined in text. Study area 
67 

10°40' 

z 

0 

t 

k 

5 

1 OOOO' . 

1 

-. . 

COSTA RlCA 

86'00' 

LONGITUDE 0 w. 

85'20' 

Figure 11. Tracklines flown in the study area during flight 8. 

defined in text. 

Study area 
68 

LONGITUDE O W. 

COSTA RlCA 

I 

Figure 12. Tracklines flown in the study area during flight 9. 

defined in text. Study area 
69 

lOO40’ 

i 

0 

1 0’00’ 

COSTA RlCA 

86’00’ 

LONGITUDE O W. 

85’20’ 

Figure 13. Tracklines flown in the study area during flight 10. 

defined in text. 

Study area 
70 

i 

a 

t 

a 

0 

w 

3 

lJ 

1 OOOO’ 

COSTA RlCA 

LONGITUDE O W. 

Figure 14. Tracklines flown in the study area during flight 11. 

defined in text. Study area 
71 

10°40' 

1 OOOO' 

LONGITUDE O W. 

Figure 15. Tracklines flown in the study area during flight 12. 

defined in text. 

Study area 
72 

1 Oo4C 

1 O"O0 

LONGITUDE O W. 

Figure 16. Tracklines flown in the study area during flight 13. 

defined in text. 

Study area 
73 

i 

n 

t 

a 

0 

w 

3 

t4 

1 0 ‘40’ 

1 OOOO’ 

LONGITUDE O W. 

Figure 17. Tracklines flown in the study area during flight 14. 

defined in text. 

Study area 
74 

1 Oo4C 

i 

0 

w 

3 

l1 

n 

t 

a 

1 OOOO' 

I 

I 

I I I' 

jj 

i 

'\. 

jJ . 

, 

i 

I 

! 

I 

i 

'. 

LONGITUDE O W. 

Figure 18. Tracklines flown in the study area during flight 15. 

defined in text. Study area 
75 

10'40' 

2 

0 

l4 

a 

COSTA RlCA 

1 0'00' 

86'00' 

LONGITUDE O W. 

85'20' 

Figure 19. Tracklines flown in the study area during flight 16. 

defined in text. 

Study area 
76 

APPENDIX I 

The experimental design required that the study area be surveyed 

approximately uniformly for all vari ab1 es. Data encountered during the 

various sun glare conditions were partially selected by manipulating the 

direction of travel of the plane during each flight. Data encountered during 

the various sea state conditions could not be selected but were recorded as 

encountered. During the survey, Flight 1, a training flight, and Flights 2, 

3, and 4 were used to determine an area where sea state conditions were 

uniform. It was perceived empirically that the northern, southern and far 

offshore regions covered by these flights had higher sea states than the more 

inshore region, therefore, the majority of the subsequent flights were 

conducted closer inshore. Inspection of the spatial distribution of effort 

conducted during good (Beau forts 0-2) and poor (Beauforts 3-6) conditions 

(Figures Al-1 and A1-2) confirmed the empirical observations. The study area 

was defined from 9" 41' to 10" 40" latitude and from 85" 20' to 86" 21'W 

1 ongi tude. The 1 ocation of the western boundary was pl aced conservati vely to 

insure sea state conditions were spatially distributed in the study area and 

to reduce the inclusion of bias owing to onshore-to-offshore density 

gradients. 
77 

1 1000' 

i 0 

F 

5 

1 OOOO 

Qo2C 

I I I I 1 I I I I I I I I I 1 I I I I I I I I I 

I 

LIERIA 

0 

COSTA RlCA 

1 I IS1 I I I I 

/ 

1 I 

1 

I I 

I 

I 

I I'I I I 

I I 

I 

1 

86O50' 86OOO' 85O20' 

LONGITUDE OW. 

Figure AI-1. Tracklines surveyed with good sea state conditions 

(Beauforts 0-2) during flights 2-16. 
78 

11OOO 

OOOO 

0°20 

E 

4 LIBERIA 

0 

Figure AI-2 Tracklines surveyed with poor sea state conditions 

(Beau forts 3-61 during fl i ghts 2-16. 
79 

APPENDIX I1 

Summary of Time-Lost Problems 

The major time lost occurred prior to the outset of 

survey was originally scheduled to begin January 2; however, 

an engine fire, encountered by the contractor while comp 

project forced the scheduled departure to January 12. 

the survey. The 

del ays, i ncl udi ng 

eting an earlier 

On January 12 the plane took off from the contractor s home office in 

Groton, Connecticut to ferry to Naples, Florida, the designated home base for 

the survey. Immediately after take off the landing gear malfunctioned and 

could not be lowered into the landing position. The plane was forced to 

complete a wheels-up landing at the Groton airport. Damage to the aircraft's 

frame was minimal. However, both engines had to be replaced. The plane was 

repaired and was flown to Naples, Florida on February 12 after a lapse of 31 

days. 

The scientific crew departed San Diego for Costa Rica via commercial 

airline on February 13, but the survey airplane, which had departed Naples for 

Costa Rica, encountered rough weather and had to return to Naples. 

Additionally a mechanical problem with the landing gear was found. The plane 

finally arrived in San Jose, Costa Rica on February 22 after a delay of 10 

days. 

During the next few days several problems were encountered: an aerial 

photography camera which had been air "expressed" to San Jose did not arrive 

for two weeks, and then was impounded by customs; one additional aircraft seat 

for the observer team was required; and camera mounts had to be custom made 

and installed. However, the most serious problem was a continuous 30-40 knot 

crosswind blowing across the single runway at the San Jose airport. The AT-11 

airplane has a tail landing wheel, which makes the plane very difficult to 

control on landing in crosswinds greater than 20 knots. An alternate airport 

at Liberia, Costa Rica was located. Aviation fuel was not available at the 

airport, but arrangements were completed for fuel to be trucked to Liberia, 

and the base of operatons was moved to Liberia on March 6 after a delay of 13 

days. 

Flight 1 occurred on Harch 7. The tachometer broke inflight, and a 

replacement was flown to San Jose from Naples. The part was installed and 

flight 2 was made on March 9 after a delay of 1 day. 

The morning segment of flight 3 was completed on March 10, however, 

electrical power to the gas pump used to refuel the airplane had been 

disconnected and the afternoon segment was cancelled. 

Flights 4 through 7 were made on schedule. The morning segment of flight 

8 was made but the afternoon segment was cancelled because of a lack of 

fuel. Additional fuel was obtained and flights 9-13 were made on schedule. 
80 

The flight crew began a required scheduled 100-hour maintenance check of the 

aircraft on March 24. Several needed repairs were identified, including a 

dead battery, faulty propellor governor, and a cracked cylinder head. 

Replacment parts were obtained and on March 31 flight 14 was attempted, 

however, the ONS failed. A replacement was obtained and flight 14 was finally 

made on April 3 after a delay of 13 days. 

Flight 15 was made on April 4 and flight 16 on April 5. The operation of 

the ONS during off-track circling was interinittent and finally completely 

malfunctioned. The decision was then made to terminate the stgdy and the 

scientific crew returned to San Diego on April 7. 
RECENT TECHNICAL MEMORANDUMS 

Copies of this and other NOAA Technical Memorandums are available from the National Technical 

Information Service, 5285 Port Royal Road, Springfield, VA 22167 Paper copies vary in price. 

Microfiche copies cost $3 50 Recent issues of NOAA Technical Memorandums from the NMFS 

Southwest Fisheries Center are listed below 

NOAA TM NMFS SbVFC 17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

Local stability in maximum net productivity levels for a simple model 

T POLACHECK 

(April 19811 

Environmental data contouring program EDMAP2 

L EBER 

(April 1982) 

The relationship between changes in gross reproductive rate and the 

current rate of increase for some simple aqe structured models 

T POLACHECK 

(May 19821 

Testing methods of estimating range and bearing to cetaceans 

T D SMITH 

(1982) 

of porpoise population sizes 

aboard the R/V D S Jordan 

'An annotated bibliography of the ecology of co-occurring tunas 

(Kafsuwonus pelamis. Thunnus albacares) and dolphins (Stenella 

attenuata, Stenella longirostris and Delphinus delphis in the 

eastern tropical Pacific" 

S D HAWES 

(November 1982) 

Structured flotsam as fish aggregating devices 

R S SHOMURAandW M MATSUMOTO 

(November 1982) 

Abundance estimation of dolphin stocks involved in the eastern 

tropical Pacific yellowfin tuna fishery determined from aerial and 

ship surveys to 1979. 

R. S. HOLT and J. E. POWERS 

(November 1982) 

Revised update and retrieval system for the CalCOFl oceanographic 

L. EBER and N. WILEY 

(December 1982) 

A preliminary study of dolphin release procedures using model purse 

D. B. HOLTS and J. M. COE 

(December 1982) 

"Possible effects of sampling biases on reproduction rate estimates 

TOM POLACHECK 

(January 1983) 

data file. 

seines. 

for porpoise in the eastern tropical Pacific."