NOAA Technical Memorandum NMFS 

JANUARY 1986 

PROPORTIONS OF SPECIES OF DOLPHINS 

IN THE EASTERN TROPICAL PACIFIC 

Jay Barlow 

Rennie S. Holt 

NOAA-TM-NMFS-SWFC-56 

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 and 

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. 
NOAA Technical Memorandum NMFS 

This TM series is used for documentation and timely communication of preliminary results. tmlerirn repor(s. or 

special purpose information. and have nci received complete formal revew. ediwial control, or detailed edlbng 

JANUARY 1986 

PROPORTIONS OF SPECIES OF DOLPHINS 

IN THE EASTERN TROPICAL PACIFIC 

Jay Barlow 

Rennie S. Holt 

Southwest Fisheries Center 

National Marine Fisheries Service, NOAA 

La Jolla, California 92038 

NOAA-TM-NMFS-SWFC-56 

U.S. DEPARTMENT OF COMMERCE 

Malcolm Baldrige. Secretary 

National Oceanic and Atmospheric Administration 

Anthony J. Calio, Administrator 

National Marine Fisheries Service 

William G. Gordon, Assistant Adminlstrator for Fisheries 
CONTENTS 

ABSTRACT ........................................................... 

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

MATERIALS .......................................................... 

Research Vessels .............................................. 

Tuna Vessels .................................................. 

Vessel Comparisons ............................................ 

ANALYTICAL PROCEDURES .............................................. 

Testing Differences ........................................... 

Variances in Species Proportions .............................. 

Sampling Error ........................................... 

Observer Error ........................................... 

Nearest Neighbor Analyses ..................................... 

RESULTS ............................................................ 

Variances ..................................................... 

Geographic Heterogeneity ...................................... 

DISCUSSION ......................................................... 

Bias and Precision ............................................ 

Research vs . Tuna Vessels ..................................... 

Area Effects ............................................. 

Searching Methods ........................................ 

Geographic Heterogeneity ................................. 

Sighting Efficiency ...................................... Recommendations ............................................... 

SUMAMRY ............................................................ 

ACKNOWLEDGEMENTS ................................................... 

LITERATURE CITED ................................................... 

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3 

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4 

5 

7 

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11 

11 

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13 

13 

14 

14 

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17 

c 

i 
L I ST OF TABLES 

Page 

TABLE 1. Dolphin species proportions from tuna and research vessel 

sighting data. Values include both weighted and 

unwei ghted averages of the species proportions i n 5-degree 

geographic strata ........................................ 18 

2. Bootstrap results testing the significance of various 

sighting factors on estimates of species proportions. 

Stratification of the sighting factors is described in the 

text. For each test, numbers represent the probabil ity 

that observed species proportions in each of the strata 

could have been drawn randomly from a sample consisting of 

all strata pooled ........................................ 19 

3. Dol phin species proportions from tuna and research vessel 

sighting data, stratified by a smeared estimate of the 

perpendicular distance from the school to the ship's trackI i ne. Val ues are weighted averages of the species proportions in 5-degree geographic strata ...................... 20 

4. Dolphin species proportions from tuna and research vessel 

sighting, data stratified by the sighting cue. Values are 

weighted averages of the species proportions in 5-degree 

geograph ic strata. Tuna vessel si ghti ngs i ncl ude on1 y 

those whose smeared perpendicul ar distances are less than 

3 nautical miles ......................................... 21 

5. Dolphin species proportions from tuna and research vessel 

sighting data, stratif led by the observer's (SI 1 estimate 

of total school size. Val ues are weighted averages of the 

species proportions in 5-degree geographic strata. Tuna 

vessel sightings include only those whose smeared perpendicular distances are less than 3 nautical mailes ........ 22 

6. Dolphin species proportions from tuna and research vessel 

sighting data, stratified by year. Values are weighted 

averages of the species proportions In 5-degree geographic 

strata. Tuna vessel sightings include only those whose 

smeared perpendicular distances are less than 3 nautical 

miles ................................................... 23 

7. Dolphin species proportions from tuna and research vessel 

sighting data, stratif led by the sea state. Val ues are 

weighted averages of the species proportions in 5-degree 

geographic strata. Tuna vessel sightings include only 

those whose smeared perpendicul ar distances are less than 

3 nautical miles.......................................... 24 

ii 
LIST OF TABLES (continued) 

8. Dolphin species proportions from tuna and research vessel 

sighting data, stratified by season. Val ues are weighted 

averages of the species proportions in 5-degree geographic 

strata. Tuna vessel sightings include only those whose 

smeared perpendicul ar distances are I ess than 3 nautical 

miles ..................................................... 

Page 

9. 

10. 

11. 

12. 

13. 

Dolphin species proportions from tuna vessel sighting data, 

stratified by whether the observer was Iton efforttt or Itoff 

effort" at the time of the sighting. Values are weighted 

averages of the speci es proportions i n 5-degree geographic 

strata. lncl uded are sightings whose smeared perpendicul ar 

distances are less than or equal to 3 nautical miles ..... Dolphin species proportions from tuna and research vessel 

sighting data, stratif led by distance from previous 

sighting. Strata are based on eucl idean distance rounded 

to the nearest degree (latitude and longitude are considered equivalent, see text for methods). Values are 

weighted averages of the species proportions in 5-degree 

geographic strata. Tuna vessel sightings include only 

those whose smeared perpendi CUI ar distances are I ess than 

3 nautical miles .......................................... 

Dol phi n species proportions from tuna vessel si ghti ng data, 

stratified by whether the original sighting was made from 

he1 icopter or from ship. Val ues are weighted averages of 

the species proportions in 5-degree geographic strata. 

Included are sightings whose smeared perpendicular distances are less than or equal to 3 nautical miles ......... 

Species proportions for research vessel cruises within 

three geographic regions: inside the 1979 aerial survey 

area, outside that area and north of the equator, and outside that area and south of the equator. Val ues are given 

as both weighted and unwei ghted averages of the proportions 

within 5-degree strata, including only those sightings with 

a school size of 15 or greater. Standard errors from bootstrap are in parentheses .................................. 

Species proportions for tuna vessel cruises within three 

geographic regions: inside the 1979 aerial survey area, 

outside that area and north of the equator, and outside 

that area and south of the equator. Val ues are given as 

both weighted and unwei ghted averages of the proportions 

within 5-degree strata, including only those sightings 

made within 3 NM perpendicular distance from the cruise 

track and with a school size of 15 or greater. Standard 

errors from bootstrap are in parentheses .................. 

25 

26 

27 

28 

29 

30 

iii 
LIST OF TABLES (continued) 

14. Species proportions for research vessel cruises within 

three geographic regions: inside the 1979 aerial survey 

area, outside that area and north of the equator, and outside that area and south of the equator. Values are given 

as both weighted and unweighted averages of the proportions within 5-degree strata, including only those sightings with a school size of 15 or greater. All sightings 

are weighted by inverse of log-school size. Standard 

errors from bootstrap are in parentheses ................. 31 

15. Species proportions for tuna vessel cruises within three 

geographic regions: inside the 1979 aerial survey area, 

outside that area and north of the equator, and outside 

that area and south of the equator. Val ues are given as 

both wei ghted and unwei ghted averages of the proportions 

w i thi n 5-degree strata, incl uding only those si ghtings 

with a school size of 15 or greater. AI I sightings are 

weighted by the inverse of log-school size. Standard 

errors from bootstrap are in parentheses ................. 32 

16. Means and standard errors of species proportions for teams 

of observers on 1982 and 1983 research vessel cruises. 

Included are only those sightings for which all observers 

on a team were able to make estimates of school size and 

species compositions, with terns A 8 C being composed of 

previous research vessel observers and teams B 8 D being 

composed of previous tuna vessel observers ............... 33 

17. Proportions of dol phin school of various species mixes 

stratified by the species mix in the preceding sighting .. 34 

18. Summary of statistical tests comparing the frequency of 

sighting a given school type, contingent on the type of 

the previous school sighted. School types were tested 

pai rw i se w i thi n 5-degree squares. Fi sher' s exact test was 

used to test whether the probabil ity of sighting a given 

school type is enhanced if the previous school was of the 

same type (1-tai I ed test). The tab1 e incl udes the number 

of species-pairs that were tested, the number of cases 

that showed a greater probabi I ity of sighting schoolsof 

one type if the previous school was of the same typerand 

the number of cases for which this enhanced probabil ity 

was statistically significant ............................ 35 

iv 
LIST OF FIGURES 

Pa ge 

FIGURE 1. Survey tracks for the 1976, 1977, 1979, 1980, 1982, and 

1983 research vessel cruises of the WV Jordan and R/V 

Cromwel L ................................................. 36 

2. Distribution of estimated sighting angles from ship's 

headings to dolphin schools at the time of initial sightings for a) tuna vessels 1976-82, b) research vessels 1976- 

8 1, and c) research vessels 1982-83 ..................... 37 

3. Distribution of estimated radial distances from ship to 

dolphin schools at the time of initial slghtings for 

a) tuna vessel s 19767-82, b) research vessel s 1976-81 , and 

c) research vessels 1982-83 .............................. 38 

4. Weighting factors, W, used for computing weighted average 

of species proportions for 51 5-degree squares. Weightings 

are based on rate of encounter for dolphin schools per 100 

search miles, mu1 tip1 led by the proportion of each area 

which is covered by ocean. Bold I ine denotes the 1979 

aerial sufiey area ....................................... 39 

5. Geographic distribution of species proportions from 

research vessel s strat if ied by 5-degree squares. Bars 

indicate re1 ative percentages of spotted, spi nner, common, 

striped, and Fraser's dol phins (from top to bottom). Nuw 

era1 s indicate number of si ghti ngs ....................... 40 

6. Geographic distribution of species proportions from tuna 

vessel s strati f led by 5-degree squares. Bars indicate 

re1 at ive percentages of spotted, spi nner, cmon, stri ped, 

and Fraser's dolphins (from top to bottom). Numerals 

indicate number of sightings ............................. 41 

7. Empirically derived distribution of X from bootstrap test 

of whether species proportions from tuna and research 

vessels are significantly different. Arrow denotes X 

value of observed tuna vessel vs. research vessel 

comparison ............................................... 42 

8. Empirical ly derived distributions of X from bootstrap test 

of whether species porportions within different strata of 

the indicated factor are significantly different for 

research vessel sighti ngs. Arrows denote observed val ues 

for the indicated test ................................... 43 

9. Empiricallly derived distributions of X from bootstrap test 

of whether species proporti.ons within different strata of 

the indicated factor are significantly different for tuna 

vessel sightings. Arrows denote observed val ues for the 

indlcated test ............................................ 44 

V 
PROPORTIONS OF SPECIES OF DOLHIINS IN 

THE EASI" TftOPICAL PACIFIC 

Jay Barlow and Rennie S. Holt 

Southest Fisheries Center 

National Marine Fisheries Service, NaAA 

La Jolla, California 92038 

CWerall proportions of the various dol&in species involved in the 

eastern Pacific tuna fishery are calculated fran sightings made fran fishing 

and research vessels. Considerable geograghic variability is found in 

dolphin proportions. Overdl species proportions are therefore calculated 

fran a weighted sum of the species proportions within S-degree geogra&ic 

strata. Variances in the estimates of these proportions are calculated 

using bootstrap methods, 

The effects of various sighting factors are tested using bootstrap 

statistics. Estimates of species proportions fran data collected on tuna 

vessels are found to be significantly different fran estimates based on 

research vessel data. Support is given for the superiority of research vessel 

estimates Over those made fran tuna vessel sightings. Other factors tested 

include sighting distance, sighting cuer school sizer year, sea stater season, 

search effort, sighting platform, and distance fran previous sighting. 

Nearest neighbor analyses show considerable geographic heterogeneity 

in species canpositions, even within 5-degree squares. Schools of like 

species are clustered together. These results emghasize the importance of 

randan or systematic search ljltterns in surveys of dolghin species proportions. 

The relative proportion of various dolphin species in the eastern 

tropical Pacific (ETF9 has plqed an important role in the estimation of 

dolphin population sizes. In current estimation procedures, species 

proportions fran tuna and reseach vessel sightings are used to prorate total. 

dolphin density estimates (derived fran aircraft line-transects) to obtain 

individual species density estimates (Hat and Fuwers, 1982). These 

estimates of species proportions have not incorporated information on the 

finescale geograghic distribution of individual species. In this paper 

we examine sane factors which affect the estimates of overall species 

proportions fran tuna and research vessel sightings, prticularly the effect 

of the geograghic distribution of species. 

Our studies of dolphin abundance (and therefore species proportions) 

are designed to assess the effect of the tuna fishery on dolphin 

populations in the GTP. Three species, the spotted dolphin (Stenel& 

attenuaa), the spinner dolphin (S. Jong irostris), and the common 
2 

dolphin (Pelcki inus delchWt 

predaninant species which have 

a result of tuna purse seining 

were considered 

ken subject to 

(Smith, 1979). 

because they are the 

incidental mortality as 

In addition, the striped 

dolphin (S. coefbleoalba) and the Fraser's dolphin (m bsei) were included because these two species are difficult to 

distinguish fran the other three during aerial transects and thus are 

included in total dolphin density estimates. Also, several of the five 

species often swim together to form multi-species aggregations. Proration 

of dolphin abundance fran aerial survey density thus requires the inclusion 

of all five species. Esthted geographic distributions for the stocks of 

the four most abundant species are given by Perrin, Scott, Walker, Wston 

and Au (1983). 

MATERIALS 

mta for this report were gathered by technicians and scientists 

aboard United States registered tuna purseseiners and National Oceanographic 

and Atmospheric Administration (NOAA) research vessels. All observers were 

trained and enacyed by the National Marine Fisheries Service ("SI. 

Research Vessels 

Research cruises were designed to survey the area inhabited by 

those dolphin species affected by the tuna fishery. Both the NOAA ship 

David Star€ Jordan and the NOAA ship !Cownsend Crcmwell were used 

to survey this area frcm January to March of 1976, 1977, 1979, and 1980; 

the Jordan alone was used in October to November 1977~~ fran May to 

June 1982, and frcm January to March 1983. Cruise tracks are shmn in 

Figure 1. The areas surveyed varied somewhat fran year-twyear: cruises 

in 1977 concentrated effort on the outer boundary of dolphin ranges; 

cruises in 1979 extensively surveyed the inshore calibration area (an area 

used to calibrate aerial and ship sighting rates, Holt and Puwers, 1982) 

and (for the Craw ell) along the equator; the 19800and 1982 cruises 

surveyed the calibration area and offshore around 10 north laotitude; 

and the 1983 cruise surveyed the calibration area and along 10 south 

latitude. The portion of the 1983 Jordan cruise, in which a helicopter 

was used in a sighting experiment, is not considered here. 

During searching hours, two observers searched the seas ahead and to 

the side of the ship for signs of marine manmals using 20-25 power pedestal 

mounted binoculars. The observers rotated every 20-60 minutes with off-duty personnel to avoid fatigue. The ships approached the animals that were 

sighted to make species identifications and school size estimates. Data 

collected for each sighting included the time, date, and position of the 

sighting; the sea state at the time of the sighting; the angle fran the ship's 

track and the estimated distance to the sighting; the initial cue that drew 

the observer's attention to the sighting (splashes, birds, or the mamnals 

'Cruise reports available fran NOAZb NMF'S, Southest Fisheries Center. 

Reference nunbers for cruises are 168, 169, 213, 214, 319, 463t 464, 

598, 599, 801, and 843. 
3 

themselves); the observers' estimates of school size; and an estimate of 

the percentages of each species present in the school. Three different 

values were recorded for school size: a best estimate, a low or minimun 

estimate, and a high or maximum estimate. 

On cruises fran 1976 to 1980, school sizes and species proportions 

were a consensus estimate by all observers on a cruise. In 1982-83, 

school sizes and species proportions were recorded independently for each 

of 1 to 6 observers. These individual estimates of school size and species proportions were averaged to give a single, concerted estimate for each 

sighting. In cases where observers recorded conflicting species identificatioy, a pnel of2 experts in mariy rtErmmdl identification 

(A. C. Myrick I W. F. Perrin I and M. D. Scott 1 reviewed the sighting 

forms and conferred with cruise leaders to arrive at concerted estimates. 

The panel considered each observer's drawings, photographs, written 

narratives, and experience in determining species identifications. 

Tuna Vessels 

Tuna vessel data used in this report were gathered on 483 cruises 

during 1976-82. Observers were placed aboard tuna vessels by "S to 

gather data on sightings (similar to research vessel data), as well as data 

on tuna-net mortality and dolphin life history. When an observer was 

actively searching under good sighting conditions (usually using 7 power 

hand held binoculars), sightings were recorded as being "on effort." These 

included many sightings that were first observed by the tuna vessel crew 

using 20-25 mer binoculars and then pointed out to the observer. The 

observer also recorded data on schools detected by the crew while the 

observer was not searching. These sightings were designated as occurring 

"off effort." The observers recorded crew estimates of school sizes 

and species proportions, but crew identifications were typically general I 

so only the observers' estimates were used in our study. The decision 

to investigate schools at close range (which greatly facilitates species 

identification) was made by the ships' Eprsonnelt and may have been 

influenced by the appraised likelihood of finding tuna. 

Vessel Ccanparisons 

There were several major differences in the way the sighting data 

were collected by observers aboard research and tuna vessels. First, research 

vessels follmed @armed cruise tracks, while the search patterns of tuna 

vessels were determined by the perceived availability of tuna and 

operational logistics (port call, breakdowns, etc.). Second, once a 

dolpkin sighting was made, research vessels pursued the school of dolphins 

until a decisive species idlentification was made, whereas on tuna vessels 

the decision to pursue a school was more related to the possibility of 

~ 

2Affiliated with NaAA, National Marine Fisheries Service. 

3Affiliated with the Inter-American Tropical Tuna Cmmission. 
4 

finding tuna. Not all schools were approached by tuna vessels 

for accurate species identification. Third, only one technician was 

aboard a tuna vessel versus 2-6 observers on duty aboard research vessels. 

School sizes and species proportions frarn tuna vessels were a single 

person's estimate rather than a consensus or a concerted estimate, as they 

were for research vessels. Finally, shipbased helicopters were 

occasionally used by tunzevessel crew to make initial sightings (observer 

esthates of species canposition and school size were made fran the deck 

of the vessel, not the helicopter) r whereas none of the research vessel 

sightings included here was made fran a helicopter. 

Sighting data fran both of these vessel types share me weaknesses. 

The angles and distances to a sighting were usually rough estimates. 

Angles were judged visually or from chan%es i% ShipAs heading. They shm 

clustering around certain valws (eg. 0 I 30 I 45 8 etc.) (Fig. 2arb)r 

which is attributed to rounding of values. An exception was the 1982-83 

research vessel cruises where a calibrated collar on the binocular mount 

was used to read angles more precisely (Fig. 2c). Distances were estimated 

visually or fran transit time and were usually rounded to the nearest nautical 

mile (Fig. 3arb). Again the 1982-83 research cruises were an exception; 

distances were estimated fran the angle between the mammals and the horizon 

using ocular reticles (Fig. 3c). Estimates of school size and species 

canposition were subject to similar rounding problems. 

Species proportions were calculated for each of the 5 species 

and for a sixth category that included unidentified dolphins. The total 

nunber of dolphins sighted in each of these species categories for a 

given area was calculated by multiplying the observer's best estimate of 

school size for each sighting by the observer's estimate of the species 

proportions and sLprming this product for all the sightings within that 

area. Proportions were canputed by dividing the estimate of the total 

nunber of individuals Seen for each species category by the total for all 

5 (or 6) categories. Unidentified dolphins that were excluded 

were not prorated into any of the other 5 categories. 

Geographic stratification was based on 5' latitude by 5' longitude 

squares. Greater than 99% of all sightings fell in 51 of the 5-degree 

squares (Fig. 41, and the rynder was lwnped into an "other" category. 

Sightings made north of 25 north latitude were not included in the 

calculation of species proportions since this area is outside the range 

of spotted and spinner dolphins (Perrin et al. 1983). 

Overall species proprtions were estimated from the S-degree 

geographic strata by a weighted average of the proportions within the 

individual strata. An estimate of the relative abundance of all dolphin 

species within a 5-degree square was used as the weighting factor for each 

square. Relative dolphin abundance was estimated as the nunber of dol#in 

schools encountered per 100 nautical miles (NM) of searching effort by tuna 

vessels (Fig. 4; data for 1977-80 fran T. Polacheckt methods presented by 

Polacheckr 1983). For ccrnparisont species proportions were also calculated 
5 

fran an weighted iwerage of the proportions within S-degree squares. 

Tkn factors were examined to determine their effect on overall 

species proportions. %ese were vessel type (tuna versus research), year, 

season, sighting cuer sea state, school size, effort (whether a sighting was 

made while the observer was actively searching) I sighting platform (helicopter 

versus ship), perpendicular sighting distance, and distance fran the last 

sighting. The bases for stratifying the last two are explained belm. 

PerpendicUdar distance refers to the normal distance fran the 

school to an imaginary line along which the vessel was traveling at the 

time of the sighting. Perpendicular distance, d, was computed fran the 

estimates of sighting angle, at and radial distance, rr as 

d = resin (a 1 (1). 

As mentioned above, sighting angles and distances were subject to 

considerable imprecision due to rounding. An inordinately large nunber 

of sighting angles were recorded as zero Le. on the track line), which 

resulted in a large nunber of zero perpendicular distance estimates. In 

order to canpensate for this bias the distribution of sighting angles was 

snoothed by adding a uniformly distributed random nunber between +5 and -5 

degrees to each sighting angle. Similarly, the distribution of radial 

distances was smoothed by adding a random nunber between +0.5 and -0.5 

nautical miles to each sighting distance. Examination of the distributions 

of sighting angles and distances (Figs. 2 & 3) indicates that this level 

of snoothing is appropriate for the observed rounding error. Perpendicular 

distances were canputed fran these snoothed angle and distance measures. 

This technique has been referred to as "smearing" in line transect work 

on marine mmals (Butterworth, 1982; Hamnond and Laaker 1982). During 

1976 tuna vessel cruises, sighting angles were often measured after the 

vessel turned tmards the dolphin school; thus, perpendicular distances 

from 1976 tuna vessel cruises were not used. 

Distance fran the last dolphin sighting was calculated using 

latitude and longitude positions. Degrees and minutes were converted 

to degrees and hundredths of degrees, and straight-line distances were 

estimated using the Pythagorean theorem. For simpl icity I distances 

were rounded to the nearest degree, and degrees of latitude and 

longitude were considered equivalent. 

Testing Differences 

A Monte Carlo technique known as bootstrap (Efron, 1979) was used 

to test the statistical significance of differences observed in the 

species proportions between two or more groups. %e null hypothesis of 

this test was that all subsanples could have been drawn randomly fran 

the set of pooled sightings. The method involves determining empirically 

the probability that a more extreme difference in species proportions 

could have been drawn randomly fran the pooled set of sightings. This 

corresponds to alpha, the probability that a true null hypothesis will be 

rejected <- I error). 
6 

The methods used here are best illustrated with an example. Assune 

we have 100 sightings of which 25 were taken in 1977 and 75 in 1978. We 

wish to test whether the species proportions observed in these two years 

were significantly different. From the pooled set of 100 sightingsr 25 would 

be selected randomly and species proportions would be calculated separately 

for these 25 and for the 75 remaining sightings. An index of dispersion 

would be used to measure the difference between the species proportions in 

the two groups. This process of selecting randan groups would then be 

repeated many times in order to determine empirically the distribution of 

the chosen index. The observed dispersion statistic franwe canprison of 

species proportions for the 1977 and 1978 sightings could then be mpred 

with the empirically-determined distribution of that statistic in order to 

infer probability levels. 

The choice of a statistic to act as an index of differences in species 

proportions is sanewhat arbitrary. In this report, a sun of squared deviations 

was used. The statistic, XI was canputed as 

i 

where E. is overall proportion of species it and 0.. is observed proportion 

of spedes i in group j. x is thus a SUR of &red deviations of the 

observed species proportions in the groups fran their expected values. 

!The simple example above is made more cunplicated if geograghic 

differences in species proportion are considered. For instancet the 1977 

sightings could have been made in areas where one species dominated and 

the 1978 sightings auld have been made in another area where a different 

species daninated. In order to test for real differences between years 

rather than geogramc differences, the subsampling would have to be 

done on a finer geographic scale. For this reason, randan subsampling 

was applied to the pooled sanae within 5-degree squares. The null 

hypothesis would thus be that the observed overall species proportions 

could have been drm randomly fran the total Sample if random sampling 

occurred within geographic strata. 

MultigiLe testing presents a problem in interpreting any analysis 

that irnrolves a nlmber of one-way mprisons. The true alFha level for 

a series of "n" independent tests is approximated by a / nr where a is 

the effective algha level that is desired. %e rejection criterion for 

the 17 tests presented here would make the rejection of any single null 

-thesis very difficult if all tests were performed simultaneously. 

Instead1 we have structured the tests hierarchically in the ranked order 

of perceived importance. Thus the effect of vessel type was tested at 

3 = 0.05. Perpendicular distance effects for both vessel types were 

tested next with a = 0.05 / 3 (note: n = 3 because there was one firstrank test and two simulWus, second-rank tests). Sighting cue for both 

vessel types was tested next with a rejection level of a = 0.05 / 5. The 

obsemed probability of subsequent tests are reported without attempting 

to interpret significance. This was done because of the rapidly decreasing 

ability to discriminate a false null kypothesis, plus ccanplications imposed 

ky lack of independence between tests. Multi-way tests were not considered 
7 

because methods for these have not been developed. 

Variances in Species Proportions 

Imprecision in estimation of species proportions could result 

fran at least two different sources. First, due to random error, the 

sample of dolphin schools encountered by survey vessels may not be truly 

representative of the entire population of dolmin schools. Second, 

species canpositions and school sizes of sightings are themselves 

estimates, and as such they are subject to error. Different methods 

were used to address these two sources of imprecision. 

Sampling Error 

Variance due to random sampling error was examined using another 

bootstrap method. We created estimates of species proportions within each 

5-degree square by randdy subsampling fran aggregate groups of sightings. 

If 100 sightings were actually seen in a given squarer sub-samples of 100 

would be dram fran the aggregate me (with replacement). This was 

repeated for all 52 geographic strata, and overall species proportions were 

calculated as above fram weighted averages of proportions within geogramic 

strata. If the aggregate sample is large enough to adequately represent 

the distribution of sightings in the underlying population, sub-sampling in 

this manner can be used to estimate variances or confidence limits (Efron 

1982). In this application, variances were calculated fran 200 randomly 

selected subsmples in each of the 52 geographic strata. 

The variances that we calculated by this method do not exactly 

correspond to the variance in our averages of S-degree squares (as reported 

in Tables 1-81. Ideally we would have designed this bootstrap approach 

to create estimates for a given 5-degree geogramic strata by randcmly 

sub-sampling only those sightings occurring within that strata. 

Unfortunately, with the 5-degree stratification sample sizes would be 

insufficient to ensure that the underlying distribution of species 

canposition is represented by the sightings in each strata. Variance 

estimates would be too conservative. 

Given the methods described above, variance in species proportions 

will tend to be overestimated if the distribution of species proportions is 

geographically heterogeneous. The estimates of species proportions within 

S-degree squares are drawn fran the aggregate population of sightings, 

rather than fran a more limited, lo& population of sightings. The method 

does not, hawever, include variability due to error in estimating the 

relative abundance weightings, nor does it include variation due to error 

in estimating the school sizes and species cunpositions of individual 

sightings (see below). We therefore believe that our variance estimates 

are more likely to be underestimates. 

Means and standard errors were calculated for species proportions 

of three geogramic areas which correspond to the statistical areas used 

in previous dolphin population estimations (Holt and Fwers 1982). These 

areas are 1) inside the 1979 aerial survey region, 2) outside that region 
8 

and north of the equator, and 3) outside that region and south of the 

equator (Fig. 4). For canprison with previous estimates, only sightings 

with an estimated school size greater than 15 were included. 

Observer Error 

Imprecision also results fran inaccuracy in estimating the species 

canpsition and school size of a sighting. Wo obsenrers may see the same 

schools and yet arrive at different estimates of overall species 

proportions. Sane data have been collected on this type of variability 

fran the 1982 and 1983 research vessel cruises. 

On the 1982 and 1983 research vessel surveys the observers were divided 

into two teans of three people. Each cruise had one team whose members had 

previous experience on tuna vessels and one team whose members had previous 

experience on research vessels. M6nbers of the same team always worked 

together, rotating duty with the other team. Frequently all three members 

of a team were able to give independent school size and species canpsition 

estimates for a given sighting. These data were used to calculate the 

overall species proportion for each individual observer based on the 

subset of his sightings that were seen by all menbers of his team. 

This yielded three independent sets of estimated species proportions for 

the same set of sightings. Means and standard errors were calculated 

for the proportions of spotted, spinner, commonr and striped dolphins for 

all 4 teams. 

Nearest Neighbor Analyses 

A simple type of nearest neighbor analysis was used to examine 

spltial heterogeneity on scales finer than 5-degree squares. If all 

species are distributed randomly within an area, the probability of 

sighting a given school type will be independent of the previous school 

seen. If schools of the sane species tend to be spatially aggregated, 

the probability of sighting a given spcies becanes contingent on 

previous sightings. 

Because schools Often Contained more than one species, schaols 

were classified by the mix of species present. The categories used were 

>90% spotted, >90% spinner, >90% canonr >90% striped, >90% spotted plus 

spinner, and "other mixed" schools. 

sightings were considered adjacent if they were made on the same 

cruise and in the sane 5-degree square. The nllf3er of sightings in each 

of the above categories was tallied, contingent on the category of the 

previous sighting (thus creating a 6 x 6 contingency table). 'Ihe elapsed 

time and distance between sightings were not considered. The significance of differences in species proportions was tested using chi-square 

oontingency tests (for n x n canparisons) and Fisher's exact test (for 

2 x 2 canparisons). Categories were excluded fran the chi-square test 

if cell frequencies fell below 5. Fisher's exact test was performed only 

if all marginal totals were greater than 5 and if the grand total was 

greater than 20. 
9 

RESULTS 

Ihe geographic distributions of species proprtions are illustrated 

in Figure 5 (fran research vessels) and Figure 6 (fran tuna vessels) for the 

five species. Geographic differences can be seen in the relative proportions of these species. Proportions in the 5-degree 2quares &ow positive 

correlations between research and tuna vessels (r = 0.43, 0.37, 0.57, 

and 0.59, respectively, for spotted, spinner, carmom and striped dolrnins). 

Research and tuna vessel data shm similar patterns of species distibution. 

Overall species proportions were calculated as weighted and 

Weighted averages of the 5-degree strata (Table 1). Despite similarities in gross ptternst large differences were evident in the 

overall distribution of s'pecies sighted fran research vessels and tuna 

vessels. Research vessel sightings shaved a lmer fraction of spotted 

dolphins. Also there were consistent differences between the weighted 

and weighted averages, with the fraction of spotted dolmin being lmer 

in the weighted estimates. 

Bootstrap methods shawed that the differences between research and 

tuna vessel proportions were highly significant (p < 0.01). Fran the 

bootstrap distribution of XI it can be seen that the observed value of X 

would be extremely unlikely if that sample were drawn randcanly fran the 

(geographically stratified) aggregate smple (Fig. 7) . The overall spcies proportions given in Table 1 may be biased 

by factors that affect the sightability of different species. For 

examgile, species with larger school sizes may be seen at greater distances 

and hence may be over-represented in the samples. Nine such factors 

were considered. Results of statistical tests of the factors are sunmarized 

in Table 2 and are discussed individually belaw. 

!!%e species canposition of sightings changed markedly with the 

perpendicular distance fran a school to the ship's trackline (Table 3). 

For both research and tuna vessels, sightings made at greater perpendicular 

distance tend to have a larger proportion of sptted dolghins. Fran 

bootstrap simulations, these differences were not significant ( a! = 0.05/3) 

for research vessel data (p = 0.83) (Fig. 8) but were significant 

for tuna vessel data (p < 0.01) (Fig. 9). Spotted dolmin schools 

are apparently visible at greater distances, which would lead to 

a biased estimate of species proportions. We attempted to eliminate this 

bias by including only those sightings fran tuna vessels that were made 

within an estimated 3 NM of the trackline of the ship (note: for tma 

vessels, sightings made within 3 NM of the trackline did not shm 

a significant distance effect, and sightings within 4 NM shaved 

significant differences) . Subsequent calculations fran tuna vessel 

data therefore only included sightings made within an estimated 3 nm 

of the trackline of the ship. 

Species proportions differed when stratified by sighting cues (Table 4) . 
10 

Percentages of spotted dolphins were higher when the initial sighting cue was 

the presence of sea birds. These differences were significant for both tuna 

and research vessel sightings (p < 0.01, CY = 0.05/5) (Figs. 8 and 9). 

Species canposition in schools was found to be dependent on school 

sizes (Table 5) for research vessel (p < 0.01) (Fig. 8) and tuna vessel 

(p < 0.01) (Fig. 9) observations. For both, the larger schools tended to be 

daninated by spotted dolphins and maller schools had proportionately 

more striped and ccxrmon dolphins. 

The distributions of qecies proportions by year are given in 

Table 6 for tuna and research vessel sightings. 'Ihe geographic coverage 

for research vessels in any single year was insufficient for prcxriding an 

accurate estimate of overall species proportions. Bootstrap tests shwed that 

the annual differences for tuna vessel sightings probably did not result 

fran random variation (p = 0.02) (Fig. 9). Although the differences were 

slight, 1979 shwed a higher fraction of ccmmon dolghins in the tuna vessel 

sightings. 

Sea state was divided into four strata based on the Beaufort Scale: 

0 - 1, 2, 3, and 4+. Beaufort nunber increases with sea state, so the 

first group corresponds to the best sighting conditions. Ihe difference 

in species proportions with sea state was larger for research vessels 

(p < 0.01) than for tuna vessels (p = 0.10) (Table 7) . Variation in species proportions between the four quarters of 

the calendar year (Table 8) was greater for tuna vessels (p = 0.04) than 

for research vessels (p = 0.97). 

Tuna vessel sightings were stratified on the basis of whether the 

observer was on effort or off effort at the time of the sighting 

(Table 9). Be differences in species canpositions between these two 

categories were slight (p = 0.80) (Figs. 8 and 9). 

Species proportions appear to be independent of the straight-line 

distance fran the last sighting (Table 10) for both tuna vessels (p = 

0.92) (Fig. 9) and research vessels (p = 0.87) (Fig. 8) . Relatively few tuna vessel sightings were initially made fran a 

helicopter accanpnying a tuna vessel (325 sightings, Table 11). Of the 

schools that were sighted, a disproportionate nunber were spotted dol@in 

schodls. Perhaps due to mall Sanple size, this effect was not significant 

(p = 0.14) (Fig. 9) . 

Variances 

Standard errors were estimated for the species proportions fran 

research and tuna vessels in the three geographical areas described above 

(Tables 12 and 13) . In previous studies, a weighting factor (the inverse of 

the logarithm of school size) was used to adjust species proportions for the effects of differential sightability with perpendicular 

distance and schoal size (Holt and PCkJers, 1982). To canpare our results 

with previous Studies, we calculated species proportions and standard 
11 

errors using this weighting (Tables 14 and 15). 

Standard errors were also canputed for the species proportions 

fran the 1982 and 1983 research vessel sightings for which all members 

of a sighting team were ahle to make estimates (Table 16). Imprecision 

resulting fran observer variability in estimating school sizes and 

canpositions was mall. Given the much greater variability in proportions 

due to sampling error (even with much larger Sample sizes, Table 12)r 

observer variability can be considered negligible. 

Geographic Heterogeneity 

The presence of geograec heterogeneity in species proportions 

was tested with the nearest neighbor analysis described above. Largescale differences were tested by pooling sightings in all areas. 

The proportion of schools of a given type that was contingent on the 

type of the previous school is tabulated in Tahle 17 for all tuna and research 

vessel sightings. For the tuna vessel observations, the differences in 

species proportions were highly significant ( X2 = 8916, p << 0.001) . In 

particular, the percentages along the principal diagonals of these matrices 

(underlined values in Table 17) were consistently greater than the overall 

percentages of the given school types. Sample sizes for research vessel 

observations were too mall for the chi-square test, but again the values 

on the principal diagonal were consistently greater than the overall species 

percentages. Thus it can be concluded that the probability of sighting a 

given school type is enhanced if the previous school was of the same type. 

This result is consistent with the observation of largescale geographic 

heterogeneity (Figs. 5 and 6). 

In order to examine geographic heterogeneity on Scales that are 

finer than 5-degree squarest tests were performed on sightings pooled 

within 5-degree blocks. Because research vessel data are sparse when 

stratified on such a fine scale, tests were performed using only the 

tuna vessel data. Fisher's exact test was used to test whether the 

probability of sighting one species of dolphin is enhanced if the 

previous school was of the same type (1-tailed test). Tests were 

performed pairwise on school typs because few 5-degree squares 

(Table 18) indicate that in an overwhelming nunber of cases, the 

probability of seeing a school of a given type is enhanced if the 

previous school was of the sane type. 

contained sufficient observations for mul ti-way canparisons. Results 

DISCUSSION 

Bias and Precision 

In order to obtain the best estimate of the overall species proportions 

for dolphins of the E2Pt we wanted to eliminate all biases in our sampling 

methods, while maintaining a large mple size to increase precision. 
12 

A variety of factors may be introducing bias into the calculation 

of species canposition fran both research and tuna vessels sightings. The 

tacit assunption that has been made thus far is that sightability is the 

sane for the five species. If sane of the species are more visible than 

others, species proportions may be biased, School size, birds associated 

with dolphins, and swimning behavior may all influence sightability. 

The validity of the assunption of equal sightability must therefore 

be exmined. 

The species composition of schools varies greatly with school 

size (Table 5). Large schools have a higher fraction of sptted dol@ins 

and a much lawer fraction of striped dol@dns than mall schools. Since 

large schools are more likely to be seen at a distance than small schools, 

this would tend to bias overall species proportions. 

'Ihe presence of seabirds is camnonly used as a sighting cue since 

birds, dolphin, and tuna are often closely associated. Bird flocks are most 

comnonly associated with spotted dolphins and seldanly associated with 

striped dolphins (Table 4). Since birds miq help observers to detect 

schools at a greater distance, overall species proportions may be biased. 

The dolphin species ansidered here also differ in swimning 

behavior, Carmen dolphins appear to swim with much jmping and splashing. 

Spotted and spinner dolphins tend to be more suhnerged in the water and 

are less likely to junp unless frightened or chased. The behavior 

of these species often changes as the dol@ins are approached by a 

vessel. Spotted and spinner dolphins have learned to "run" fran vessels 

(Au and Perryman 1982). When wimning rapidly, these species becane 

easier to spot. Hewitt (1985) found that schools are usually Seen 

before this running behavior begins. 

The specieespecific differences in sightability are more 

likely to bias distant sightings than sightings that are macle near 

a vessel. Schools that are on or near the trackline of a vessel are 

likely to be seen regardless of their canposition. Bias fran all three 

of the abuve factors can be minimized if samples are limited to those 

schools that would have passed close enough to the ship to guarantee 

detection. Surprisingly, research vessel sightings shawed no significant 

changes in species proportions with perpendicular distance fran the ship; 

hence there is insufficient justification for eliminating the distant 

sightings made fran research vessels. HOwevert additional data my cause a 

reconsideration of this point given that several characteristics of 

spotted dolphins (large school sizes and ceoccurrence of birds) are 

likely to make them visible at greater distances. 

Research vs. Tuna Vessels 

Relatively large differences were seen between the species 

proportions fran tuna vessel sightings and those fran research vessel 

sightings. Similar differences have been noted in previous studies (Holt 

and Pawers, 1982). In general, tuna vessel observations include a greater 

proportion of spotted dolphin sightings and fewer sightings of striped 

dolphin. We will attempt to explain these differences in terms of factors 
13 

that affect sightings fran the two vessel types. Although our conclusions 

are speculative, we feel they are the most reasonable interpretation of 

available data. 

Since the differences in the cwerall estimates of species proportions 

fran research and tuna vessels are too large to be randan sampling error, 

alternative hypotheses must be eximined. Given the large differences in 

species canposition beheen geographic areas, the differences in 

species proportions between vessel types may have resulted fran 

large-scale differences in the areas searched. Alternatively, differences 

in the species seen could have arisen fran differences in the 

searching methods used by tuna and research vessels. Finally, although 

the vessels may have been searching in the same large-scale areas, 

the observed differences could have resulted fran fine scale geographic 

differences coupled with differences in search patterns between 

the vessel types. These hypotheses will be considered in detail belcw. 

Area Effects 

Although research and tuna vessels did not concentrate their 

searching efforts in exactly the same geographic areas, the areas 

surveyed by both mer most of the area inhabited by dolphins. 

Unlike previous estimates of species proportions, which were not adjusted 

for geographic differences (Holt and Pavers, 19821, the overall 

species proportions in this study were calculated as a weighted sun 

of species proportions in 5-degree squares. If all years are included, 

ccwerage was relatively canplete for both vessel types. Since the 

calculation of overall proportions incorporated geographic stratification, 

large-scale geographic differences in searching effort cannot explain 

these large differences in species canposition between vessel types. 

Searching Methods 

Differences in searching methods between research and tuna 

vessels can cause differences in the estimates of species canposition in 

a variety of ways. First, flocks of birds are visible at greater distances 

than schools of dolphins are, and tuna vessels are more likely to investigate 

bird flocks. In cases where seabirds were the initial cue for a dolphin 

sighting, the proportion of spotted ddlghins in the school was much higher. 

This was true for both research and tuna vessel sightings (Table 4). This 

indicates that sea birds are more likely to be associated with schools 

of spotted dolphins than with other dolghin schools. If tuna vessels 

change course to investigate bird aggregations, the proportion of spotted 

dolphins is likely to be exaggerated. Eliminating distant sightings 

should, hwever, prevent this fran biasing species proportions. 

Second, the initial sightings on tuna vessels are usually made by 

crew members. ?he crew is mostly concerned with dolphin schools which may be 

with tuna. If the crew manber decides that the sighting is not a 

good indication of the presence of tuna, the observer may not be made mare 

of the sighting or the vessel may not approach close enough for the observer 

to determine species canposition or school size. The crew has the advantage 
14 

of using 20-25x binoculars, which greatly facilitate searching. Dolghin 

schools typically include spotted dolphin schools, mixed schools of sptted 

and spinner dolphins, and occasionally camon dolghins. Consequently, 

observers may be more likely to be told about sightings of these species 

than sightings of striped or Fraser's dolghins, which seldom are associated 

with tuna. Crew members also make some observations which are recorded by 

the observer, but which the observer never gets a chance to verify. Such 

records were not used in our analyses because of their nowspecific species 

identifications (such as "black fish, " "whitebellies, " etc. 1 . 

Geographic Heterogeneity 

Although tuna vessels and research vessels searched in the same 

general geographic areas, their searching ptterns differed greatly. 

Research vessels searched systematically, f ollcwing pre-detedned 

courses. Tuna vessels searched in areas where tuna were thought to be; 

in some cases "code groups" or cooperatives relayed radio information 

about fish availability (Groom, 1980). If dolphin species are 

distributed randcmly within an area, search patterns are not likely to 

influence the averall species canposition of sightings (ignoring the 

possibility of resighting the same school). If, huwever, the distribution 

of species is related to habitat and if searching effort is limited to 

areas with distinctive oceanographic or biological features (e.g. the 

presence of tuna), overall species canpositions may be biased. Because 

the distribution of dolphin species is patchy, systematic or random search 

patterns are preferable. 

The results of the nearest neighbor analysis indicate that schools 

with similar species canposition are often found together. The cruise 

tracks of tuna vessels indicate that their search patterns are not random 

(Palacheck, 1983). Tuna vessels will usually search intensively in a 

localized area, and then move to another area and again search intensively. 

These patterns may take advantage of the tendency for schools of spotted 

dolphms to be sptially aggregated. Because dolghin species are not 

distributed randdy, this nowrandan search pattern used by tuna vessels 

is likely to result in biased estimates of species proportions, whereas the 

preplanned search pttern of research vessels are less likely to result 

in such biases. 

Sighting Efficiency 

The difference in sightings between research and tuna vessels can be 

largely explained in terms of differences in sighting efficiency of the 

various species. We define encounter rate as the nunber of schools sighted 

per 1000 survey miles. Overall encounter rate for research4 vessels in 

1977-83 was approximately 10.0 for all 5 species (Holt ,Table 3). 

4Holt, R S. 1984. Estimation of density of dolghin schools in the 

eastern tropical Pacific Ocean using line transect methods, 

Southwest Fish. Cent. Adm. Rep. No. W-84-32, La Jolla, CA. 72pp. 
15 

For research vessels, 56% of all schools included either spotted dolphins, 

spinner dolphins, or both species; 17% included ccsnmon dolphins, and 25% 

included striped dolphins. The research vessel encounter rates for individual 

species are thus 5.6 / 1000 NM for spottedhpinner schools, 1.7 / 1000 NM 

for camaon schools, and 2.5 / 1000 NM for striped schools. For these 

species groups, the corresponding values fran tuna vessels are 6.6, 0.98 

and 0.4 / 1000 NMt respectively (Polacheck 1983, Table IX-3, data fran 

1977-80). These results indicate that research vessels are as effective as 

tuna vessels in sighting spotted dolphin schools, but they are much more 

effective at sighting schools of camon and striped dolphins. 

Reccmnenda tions 

Although tuna vessel data represent a far greater nunber of sightings, 

estimates of overall species proportions fran tuna vessels sightings are 

probably biased because of the way the data were collected. Tuna vessels 

have been used as shipr4-of-opportunity. Research vessel cruises were designed 

to survey all dolphin species. Historically, the use of tuna vessel data for 

estimates of species proportions was largely motivated by the lack of 

sufficient data fran research vessels. We believe that current research vessel 

data are sufficient to estimate species proportions. 

Our best estimates are the research vessel proportions which were 

averaged mer 5-degree geographic strata (Table 12). These estimates, 

however, may be subject to errors fran factors we have not considered 

and to inaccuracies resulting fran random sampling error. It may be that 

certain species are less easily seen at all sighting distanoes. 

Estimates given in Table 12 include species proportions fran 

both weighted and weighted averages of the proportions within 5-degree 

strata. We do not feel confident in recamending one method over the 

other. The weighting factors were derived fran tuna vessel estimates of 

relative dolphin density. Since tuna vessels encounter proportionately more 

spotted dolphins, the relative density estimates may be biased toward areas 

where spotted dolphin abundance is high. Areas of high sptted 

dolphin abundance, however, may also be areas of high density for the 

other species. Urweighted averages might therefore underestimate the 

true proportion of spotted dolphins. If the abundance of other species 

is positively correlated with spotted dolphin abundance and if that 

correlation is imperfect (i.e. less than 1.01, the true species proportions 

probably lie between those estimated by the weighted and unweighted averages. 

Previous estimates of species proportions for ETP dolphins have 

used entirely different methods (Holt and Powers, 1982); thus, our results 

are not directly canparable with previous ones. Holt and Pawers used a 

method that averaged percentage canpositions in a school, without weighting 

by school size. In effect, this gave an average species canposition of 

schools rather than a percentage of individuals belonging to the various 

species (as in our estimates). Because spotted dolphins tend to form 

large schools, our estimates would tend to show a higher proportion of 

spotted dolphins than the previous estimates. Our current estimates 

of the percentage of spotted dolphins (Table 12) fall between the previous 

estimates for research vessels and those for tuna and research vessels 

pooled (Holt and Parers 19828 Table 21). 
16 

In order to prorate estimates of dolphin density fran aerial 

sumeys to population estimates for species, an overall estimate of 

dolphin species proportions is needed. Sighting observations f ran 

surface vessels can be used for this purpose if these sightings are 

representative of the actual species mix in the m. 

Tuna vessel sightings are unacceptable for this purpose for three 

reasons. First, tuna vessels are primarily interested in dolmin species 

that are likely to be associated with tuna. The crew may not relay 

information on sightings of other species to the observer. Second, 

tuna vessels will approach those dolphin schools that are likely to 

be associated with tuna. %e observer may never get an adequate look 

at other schools to estimate species canposition or school size. Third, 

tuna vessels search nowrandcunly in areas that are believed to have tuna. 

Dolphin species are not randanly distributed, but rather schools of like 

species are found clustered together. The distribution of dolphin species 

is likely to be related to the same oceanographic features that determine 

tuna distributions. Therefore systenatic or pre-planned search patterns 

are necessary to avoid biased species proportions. 

The best estimates of species proportions (Table 12) are therefore 

derived f ran research vessel observations. Because research vessel 

searching effort is not uniformly distributed geographically, estimates of 

species proportions are best averaged Over mall geographic strata. 

Ideally this averaging should be weighted by the total density of dolmins 

within each strata. Tuna vessel encounter rates can be used for this 

purpose, but these estimates of relative density may be skewed towards 

areas of spotted dolphin abundance. values from unweighted and weighted 

averages of geographic strata probably bracket the true estimates of EIF 

dolphin species proportions. 

We wish to acknowledge the efforts of the many technicians who 

were responsible for gathering the data upon which this report is based. 

The sightings used here are the result of literally hundreds of man-years 

of labor, often under difficult circunstances. Acknowledgement is also 

deserved by the data editing and management group and the graphics 

department, SIX. We thank Tan Polacheck for generously sharing his 

information on dolphin relative abundance, John Calogne provided data 

and analysis pertaining to the effects of observer error fran 1982-83 

research cruises. The statistical design used here benefited greatly 

fran discussions with T. Gerrodette, D. Goodnan, k MacCall, and R. MfAhot. 

We thank G. Broadhead, P. Hamnond, D. Chapan, J. Michalski, T. Quinn, 

G. Sakagawa, and T. Shith for their critical review of this manuscript. 
17 

LITERATURE CITED 

Aur D. and W. Perryman. 1982. Movement and speed of dolphin schools 

responding to an approaching ship. Fish. Bull. 80:371-379. 

Butterworth, D. S. 1982. On the functional form used for g(y) for 

Minke whale sightings, and bias in its estimation due to measurement 

inaccuracies. Rep. int. Whal. Cunnn. 32:883-888. 

Croant M. M. 1980. The tuna-porpoise problen: management aspects of 

a fishery. Master's Thesis, Oregon State University. 41pp. 

Efrollr B. 1979. Canputers and the theory of statistics: thinking the 

unthinkable. SIAM Rev. 21:460-480. 

EfrOn, B. 1982. The jackknife, the bootstrap, and other resamplingmethods. 

Hammond, P. S. and J. L. Laake. 1982. Trends in estimates of abundance 

of dolphins (Sten- spp. and involved in the 

purseseine fishery for tunas in the eastern Pacific Ocean, 1977-1981. 

Rep. int. Whal. Cunnn. SC/34/SMl 

Fish. Bull. 83(2) :187-194. 

SIAMi monograph 1138, CBMS-NSF. 92~~. 

Hewitt, R. P. 1985. Reaction of dolmins to a survey vessel. 

Holtt R. S. I and J. E. Powers. 1982. Abundance estimation of dolFhin 

stacks involved in the eastern tropical Pacific yellowfin tuna fishery 

determined from aerial and ship surveys to 1979. NQAA Tech. &mn. 

NoAPrTWNMF'SSVFc-23. 

Perrin, W. F., M. D. Scott, G. J. Walker, F. M. Ralston and D. W. K. Au. 

1983. Distribution of four dolphins (Stenella spp. and Il&h&US 

delphis) in the eastern tropical Pacific, with an annotated catalog of data sources. NOAA Tech. Mm. NaAA.WmsWFc-38. 65pP. 

Polacheck, T. 1983. The relative abundance of dolphins in the eastern 

tropical Pacific based on encounter rates with tuna purse seiners. 

Ph. D. Diss., Univ. Oregon. 444pp. 

Smith, T. 1979. Report of the status of porpoise stocks workshop, August 

27-31, 1979. SoutJ'west Fisheries enter, NQMu La Jolla, California. 

Adnin. Rep. No. LJ-79-41. 
18 

Table 1. Dolghin species proportions fran tuna and research vessel sighting 

data. Values include both weighted and weighted averages of the 

species proportions in 5-degree geographic strata. 

Species 

Tuna Vessels Research Vessels 

Weighted Un-Weighted Weighted UMeighted 

Average Average Average Average 

Identif ied 

spotted dolphin 0.69 0.66 0.50 0.45 

Spinner dol phi n 0.19 0.18 0.23 0.22 

Conrmon dolphin 0.10 0.13 0.15 0.18 

Stripd dolphin 0.02 0.02 0 011 0.13 

Fraser ' s dolghin 0.01 0.01 0.01 0.02 

Total 1.0 1.0 1.0 1 .o 

Unidentified 0.13 0.15 0.07 0.07 

Nunber of Dolphins 23 rlOO roo0 149 r 00 0 

Nunber of Schools 33r346 lr120 
19 

Tabl e 2. Bootstrap results testing the significance of various sighting 

factors on estimates of species proportions. Stratification of 

the sighting factors is described in the text. For each testr 

nunbers represent the probability that observed species 

proportions in each of the strata could have been drawn randomly 

fran a sample consisting of all strata pled. 

Sighting 

Factor 

Research Tuna Tuna and Research 

Vessels Vessels Vessels Pooled 

1) Vessel type 

2) Perpendicular 

distance 

0.83 < 0.01 

3) Sighting cue < 0.01 < 0.01 

4) School size < 0.01 < 0.01 

5) Year 0.09 0.02 

6) Sea state < 0.01 0.10 

7) Season 0.97 0.04 

8) Effort 0.80 

9) Distance fran 

prev. sighting 

0.87 

- 

0.92 

10) Helicopter 0.14 
20 

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21 

Table 4. Dolphin species proportions fran tuna and research vessel sighting, 

data stratified by the sighting cue. Values are weighted averages 

of the species proportions in 5-degree geographic strata. Tuna 

vessel sightings include only those whose aneared perpendicular 

distances are less than 3 nautical miles. 

Sighting Cue 

Sea Birds Splashes Mamds Overall 

TUNA VESSELS 

Identified 

Spotted dolphin 

Spinner dolphin 

Striped dolphin 

Fraser s dolphin 

Total 

dolphin 

0.73 

0.18 

0.07 

0.01 

0.00 

1.0 

0.51 

0.16 

0.23 

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0.50 

0 021 

0.18 

0.07 

0.04 

1.0 

0.682 

0.182 

0.106 

0 0022 

0.008 

1.0 

Unidentified 0.11 0.35 0.29 0.152 

Nunber of Dolghins 

Number of Schools 

7 r66W 

9r335 

1 r73 OK 

3 r675 

2 r380K 

6 r538 

11 r 800K 

191548 

RESFARCH VESSELS 

Identified 

spotted dolphin 

Spinner dolphin 

Cmnnon dolphin 

Striped dolphin 

Fraser s dolphin 

Total 

0.61 

0 -29 

0.08 

0.02 

0.00 

1 .o 

0.39 

0.19 

0.13 

0 -29 

0.01 

1.0 

0.39 

0 019 

0.13 

0.27 

0.02 

1.0 

0.504 

0.237 

0.123 

0 0120 

0.016 

1.0 

Unidentified 0.02 0.16 0.14 0.084 

Nunber of Dolphins 

Number of schools 

15K 

181 

45K 

544 

lllK 

968 

51K 

2 43 
22 

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24 

Table 7. Dolphin species proportions fran tuna and research vessel sighting 

data, stratified by the sea state. 

the species proportions in 5-degree geographic strata. 

sightings include only those whose sneared perpendicular distances 

are less than 3 nautical miles. 

Values are weighted averages of 

Tuna vessel 

Species 

Beaufort State 

0-1 2 3 >4 Overall 

mNA VESSELS 

Identified 

spotted dolphin Spinner dolphin 

Striped dolphin 

Fraser s dolphin 

Total 

dolphin 

unidentified 

Nunber of Dolphins 

Nunber of Schools 

RESEARCH VESSELS 

Identified 

spotted dolphin 

Spinner dolmn 

Camnon dolphin 

Striped dolphin 

Fraser I s dolmin 

Total 

Unidentified 

Nunber of Dolphins 

Number of Schools 

0.69 0.69 0.68 0.69 

0.13 0.17 0.17 0.18 

0.13 0.10 0.11 0.10 

0.02 0 -04 0 -04 0.02 

0.03 0.00 0.00 0.01 

1.0 1.0 1.0 1.0 

0.17 0.18 0.18 0.18 

937K lr690K lr470K 73 OK 

2r097 3r520 2r920 lr411 

0.49 0.52 0.51 0.37 

0 -14 0.20 0.17 0.26 

0.06 0.12 0.08 0.15 

0.32 0.14 0.23 0.22 

0.00 . 0.01 0.01 0.00 

1.0 1 .o 1.0 1.0 

0.16 0.10 0.17 0.16 

12K 2 9K 23K 14K 

129 237 237 192 

0.690 

0.157 

0.103 

0 -040 

0.010 

1.0 

0.170 

4r830K 

9r948 

0 -501 

0.214 

0.103 

0 -176 

0.006 

1.0 

0.105 

77K 

769 
25 

Table 8. Dolghin species proportions fran tuna and research vessel sighting 

data, stratified by season. Values are weighted averages of the 

species proportions in 5-degree geografiic strata. 

sightings include only those whose aneared perpendicular distances 

are less than 3 nautical miles. 

Tuna vessel. 

Species 

Season 

Jan-br AprJun Jul-Sep Oct-Dec Overall 

luNA VESSELS 

Identified 

Spotted dolphin 

Spinner dolphin 

Common dolphin 

Striped dolphin 

Fraser's dolghin 

Total 

0.68 

0.14 

0.10 

0 -05 

0.03 

1.0 

0.67 

0.17 

0.10 

0.05 

0.01 

1.0 

0.68 

0.19 

0.11 

0.02 

0.00 

1.0 

0.64 0.682 

0 020 0.182 

0.12 0.107 

0.03 0 0022 

0.00 0.008 

1.0 1.0 

Unidentified 0.17 0.17 0.13 0.24 0.153 

Nunber of Dolphins 

Number of Schools 

3 r850K 

5 r667 

2r270K 12 rlOOK 

3 r658 20r088 

2 r690K 

5 r553 

3 r310K 

5r210 

RESEARCH VESSE3LS 

Identified 

spottea dolphin 

Spinner dolphin 

Common dolphin 

Striped dolphin 

Fraser s dolghin 

Total 

0.44 

0 -24 

0.18 

0.12 

0.02 

1.0 

0.47 

0.18 

0.13 

0.22 

0.00 

1.0 

0.58 

0.12 

0.09 

0 021 

0 .oo 

1.0 

0.40 0.501 

0 -30 0 -225 

0.05 0.148 

0.25 0 0112 

0.00 0.014 

1.0 1 .o 

Unidentified 0.06 0.09 0.20 0.18 0.069 

Nunber of Dolphins 

Number of Schools 

116K 

895 

1 4K 

116 

6K 

44 

13K 14 9K 

65 1r120 
26 

Table 9. Dolphin species proportions frcm tuna vessel sighting data, 

stratified by whether the observer was "on effort" or "off effort" 

at the time of the sighting. Values are weighted averages of the 

species proportions in 5-degree geographic strata. Included are 

sightings whose sneared perpendicular distances are less than or 

qual to 3 nautical miles. 

Species "On Effort" "Off Effort " &erall 

'IUNA VESSELS 

Identified 

spotted dolphin 

Spinner dolphin 

Common dolphin 

Striped dolphin 

Fraser I s dol*in 

Total 

Unidentified 

Nunber of Dolphins 

Number of Schools 

0.67 

0 -19 

0.11 

0.02 

0.01 

1.0 

0.15 

6 r380K 

101737 

0.69 

0.17 

0.10 

0 -04 

0.00 

1.0 

0.15 

5 r740K 

9 r351 

0.682 

0.182 

0.107 

0.022 

0.008 

1.0 

0.153 

12 rlOOK 

20 r008 
27 

Table 10. Dolphin species proportions frm tuna and research vessel sighting 

datar stratified by distance fran previous sighting. Strata are 

based on euclidean distance rounded to the nearest degree (latitude 

and longitude are considered equivalent? see text for methods). 

Values are weighted averages of the species proportions in 5-degree 

geographic strata. 

sneared perpendicular distances are less than 3 nautical miles. 

Tuna vessel sightings include only those whose 

Distance (in degrees) frm Previous Sighting 

Species 0 1 2 3+ Overall 

TUNA VESSELS 

Identified 

Spotted dolphin 

Spinner dolphin 

Common dolphin 

Strim dolphin 

Fraser's dolMin 

Total 

Uni dent i f ied 

Nunber of Dolphins 

N&r of Schools 

RESEARCH VESSELS 

Identified 

spotted dolphin 

Spinner dolphin 

Common dolphin 

Striped dolphin 

Fraser s dolphin 

Total 

Unidentified 

Nunber of Dolphins 

Number of Schools 

0.70 

0.17 

0.11 

0.03 

0.00 

1.0 

0.14 

4r660K 

7 r206 

0.50 

0.21 

0.11 

0.17 

0.02 

1.0 

0.09 

82K 

634 

0.68 

0.19 

0.10 

0.02 

0.01 

1.0 

0.13 

3 r530K 

5r464 

0.48 

0.21 

0.13 

0.19 

0.00 

1.0 

0.16 

21K 

149 

0.68 0.67 0.682 

0.19 0.19 0.182 

0.11 0.11 0.106 

0.02 0.03 0.022 

0.01 0 .oo 0.008 

1.0 1.0 1.0 

0.16 0.18 0.153 

lr160K 2r570K llr900K 

1r959 4r875 19~504 

0.47 0.40 0.502 

0.23 0.16 0.226 

0.10 0.15 0.146 

0.20 0.27 0.112 

0.00 0.02 0.014 

1.0 1.0 1.0 

0.18 0.09 0.069 

12K 32K 148K 

106 222 lrlll 
28 

Table 11. Dolphin spcies proportions fran tuna vessel sighting data, 

stratified by whether the original sighting was made fran 

helicopter or fran ship. Values are weighted averages of the 

species proportions in 5-degree geogra*ic strata. Included are 

sightings whose smeared perpendicular distances are less than or 

equal to 3 nautical miles. 

Species 

Sighting Platform 

Helicopter Ship Overall 

mNA VESSELS 

Identified 

Spotted dolphin 

Spinner dolphin 

Common dolphin 

Striped dolphin 

Fraser's dolphin 

Total 

Unidentified 

Nunber of Dolphins 

Number of Schools 

0.79 

0.14 

0.06 

0.01 

0.00 

1.0 

0.12 

26 OK 

325 

0.68 

0 -18 

0.11 

0 -04 

0.01 

1.0 

0.15 

11 r 800K 

19r690 

0.682 

0.182 

0.107 

0 9021 

0.008 

1.0 

0.153 

12 rlOOK 

20r015 
29 

Table 12. Species proportions for research vessel cruises within three 

geogramic regions: inside the 1979 aerial survey arear outside 

that area and north of the equatorr and outside that area and south 

of the equator. 

averages of the proportions within 5-degree strata? including only 

those sightings with a school size of 15 or greater. 

errors fran bootstrap are in parentheses. 

Values are given as both weighted and weighted 

Standard 

INSIDE AERIAL =ION 

spotted 

Spinner 

Camw>n 

Striped 

Fraser s 

CUTSIDE AM) NCRIH 

OF EQUA!IOR 

spotted 

Spinner 

Canmon 

Striped 

Fraser s 

CUTSIDE AND SCUTH 

OF EQUATOR 

Spotted 

Spinner 

Cannon 

Striped 

Fraser' s 

Unweighted 

Aver age 

.39 (-042) 

-17 (.030) 

.27 (.043) 

.16 (.030) 

.01 (.003) 

Unweighted 

Average 

Umeighted 

Average 

Weighted 

Average 

.49 (.041) 

.19 (.029) 

.19 (.039) 

-11 (.025) 

-01 (.003) 

Weighted 

Average 

-53 (.OS21 

.26 (.030) 

.12 (-058) 

-07 (-038) 

-02 (-023) 

Weighted 

Average 

-25 (.094) 

-30 (.131) 

-13 (-068) 

.28 (.097) 

-04 (-083) 
30 

Table 13. Species proportions for tuna vessel cruises within three 

geographic regions: inside the 1979 aerial survey area, outside 

that area and north of the Equator, and outside that area and south 

of the equator. 

averages of the proportions within 5-degree strata, induding only 

those sightings made within 3 Nl perpendicular distance fran the 

cruise track and with a school size of 15 or greater. 

errors fran bootstrap are in parentheses. 

Valws are given as both weighted and weighted 

Standard 

INSIDE AERIAL REGION 

Spotted 

Sp' inner 

Camron 

Striped 

Fraser I s 

CUTSIDE AND NORTH 

OF EQUATOR 

spotted 

Spinner 

Common 

Striped 

Fraser' s 

m1DE m sourn 

OF EQUATOR 

Spotted 

Spinner 

Camron 

Striped 

Fraserl s 

Unweighted 

Aver age 

.59 (.013) 

.16 (.010) 

.22 (.013) 

-03 (.002) 

0001 (0002) 

Unweighted 

Average 

.70 (.022) 

-19 (.014) 

.08 (.021) 

.02 (.004) 

-01 (.003) 

Ullweighted 

Average 

.58 (.032) 

.19 (.026) 

-15 (.029) 

.08 (.012) 

0002 (.001) 

Weighted 

Average 

.65 (.012) 

.17 (.008) 

.16 (.011) 

002 (0002) 

0001 (0002) 

Weighted 

Average 

.71 (.020) 

-19 (.013) 

.07 (.020) 

.02 (.004) 

.01 (.003) 

Weighted 

Average 

.56 (.031) 

.18 (.024) 

.17 (.027) 

-08 (.012) 

0002 (.001) 
31 

Table 14. Species proportions for research vessel cruises within three 

geographic regions: inside the 1979 aerial survey areat outside 

that area and north of the equatorr and outside that area and south 

of the equator. Values are given as both weighted and weighted 

averages of the proportions within 5-degree stratar including only 

those sightings with a school size of 15 or greater. All sightings 

are weighted by the inverse of log-school size. 

fran bootstrap are in parentheses. 

Standard errors 

INSIDE AERIAL REGION 

spotted 

Spinner 

Cannon 

Striped 

Fraser s 

Spotted 

Spinner 

Gammon 

Striped 

Frer's 

spotted 

SP' inner 

Cannon 

Striped 

Fraser' s 

Unweighted 

Average 

-38 (-039) 

-16 (.028) 

-26 (.039) 

.19 (.029) 

.01 (.003) 

Unweighted 

Average 

.51 (.048) 

.26 (.029) 

-12 (-054) 

-09 (.039) 

002 (.021) 

Unweighted 

Average 

.26 (-085) 

-30 (.116) 

-10 (.059) 

-30 (.090) 

-04 (.071) 

Weighted 

Average 

.48 (-037) 

-19 (.026) 

.18 (.034) 

.14 (-025) 

.01 (.003) 

Weighted 

Average 

-52 (.049) 

.25 (-028) 

-12 (-055) 

-09 (.038) 

002 (0022) 

Weight& 

Average 

-24 (-086) 

-29 (.118) 

.13 (.061) 

-31 (.094) 

-03 (.074) 
32 

Table 15. Species proportions for tuna vessel cruises within three 

geograghic regions: inside the 1979 aerial survey areat outside 

that area and north of the quatort and outside that area and south 

of the equator. 

averages of the proportions within 5-degree stratar including only 

those sightings with a school size of 15 or greater. All sightings 

are weighted by the inverse of log-school size. 

fran bootstrap are in prentheses. 

Values are given as both weighted and weighted 

Standard errors 

INSIDE AExIAL REION Unweighted Weighted 

Average Average 

spotted 

SP' inner 

Cmmn 

Striped 

Fraser' s 

spotted 

Spinner 

Ccmmon 

Striped 

Fraser s 

aJTSI.DE ISND scum 

OF EWAIIOR 

spotted 

Spinner 

Carmon 

Striped 

Fraser' s 

-61 (.009) -66 (.007) 

-15 (.006) -17 (.005) 

021 (.009) -15 (.007) 

-03 (.002) 002 (.001) 

0001 (.001) 0001 (.001) 

Unweighted Weighted 

Average Average 

-70 (.011) .71 (.010) 

-20 (.008) -20 (.007) 

-08 (.011) .06 (.010) 

.01 (.003) 001 (.002) 

001 (.002) 001 (.002) 

Unweighted Weighted 

Average Average 

.63 (.024) .62 (.023) 

-16 (.021) -16 (.020) 

-12 (.018) -12 (.017) 

.08 (.010) -08 (.010) 

001 (.001) 001 (0001) 
33 

Table 16. Means and standard errors of species proportions for teams of 

observers on 1982 and 1983 research vessel cruises. Included 

are only those sightings for which all observers on a team were 

able to make estimates. 

independent estimates of schod size and species canpositionst 

with teams A & C being canposed of previous research vessel 

observers and teams B & D being canposed of previous tuna vessel 

observers. 

Teams were made up of 3 observers making 

19 82 1983 

TeamA TeamB TeamC WamD 

spotted dolphins 

mean proportion 0.59 0.52 0.39 0.19 

standard error (0.028) (0.010) (0.032) (0.008) 

Spinner dolphins 

mean proportion 0.23 0.17 0.16 0.20 

standard error (0.025) (0.006) (0.013) (0.055) 

Canmon dolphins 

mean proportion 0.15 0 022 0.26 0.50 

standard error (0.002) (0.008) (0.005) (0.038) 

Striped dolphins 

mean proportion 0.03 0.10 0.19 0.11 

standard error (0.003) (0.015) (0.025) (0.011) 

MEAN 

0.42 

(0 .020) 

0.19 

(0.025) 

0.28 

(0.013) 

0.11 

(0.014) 

N&r of Sighting 34 52 66 78 
m 

d 

i 

c 

8 

dp 

0 

m 

A 

5 

p1 

-4 

2 

dP 

0 

QI 

A 

I 

dp 

0 

07 

A 

& 

H 

8 

dP 

0 

QI 

A 

% E 

dp 

0 

QI 

A 

0 

0 

In 

QI 

rl 

co 

u) 

m 

In 

rl 

cv 

QI 

QI 

m 

cv 

cv 

rl 

.!I 

z 

m 

w 

VI 
35 

Table 18. Sumnary of statistical tests canparing the frequency of sighting 

a given school type# contingent on the type of the previous 

school sighted. 

squares. Fisher's exact test was used to test whether the 

probability of sighting a given school type is enhanced if the 

previous school was of the same type (1-tailed test) . The 

table includes the nunber of species-pairs that were tested# the 

nmber of cases that shwed a greater probability of sighting 

schools of one type if the previous school was of the sane typel 

and the nunber of cases for which this enhanced probability was 

statistically significant. 

School typs were tested painvise within 5-degree 

School T&ES 

Nunber Nunber Shaving Nunber Shaving 

of Pairs Geographic Significance 

Tested Heterogeneity (p < 0.05) 

>go% spotted >go% Spinner 24 24 

>90% Cammon 22 22 

>go% Striped 15 13 

>go% Spot. + Spin. 39 37 

16 

18 

10 

17 

>go% Spinner >90% Carmon 9 9 9 

>90% Striped 1 1 1 

>go% spot. + Spin. 18 15 5 

>90% Cammon >90% Striped 10 10 

>go% Spot. + Spin. 7 6 

7 

6 

>90% Striped >90% Spot. + Spin. 3 3 3 
36 

0 

0 

cu 

0 

0 

b 

t 

l- 0 

l0 
37 

TUNA VESSELS 1976-82 

n= 33,257 

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 8590 

-15.2% 

VESSELS 1976-8 1 

n= 974 

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 

10 

07 

z 

RESEARCH VESSELS 1982-83 

n= 328 

I I' 

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 

SIGHTING ANGLE 

Figure 2. Distribution of estimated sighting angles from ships' headings 

to dolphin schools at the time of initial sightings for a) tuna 

vessels 1976-82, b) research vessels 1976-81, and c) research 

vessesls 1982-83. 
38 

n 

W 

> 

a 

W 

cn 

m 

0 

c 

z 

W 

0 

W 

a 

e 

n 

W 

> 

a 

W 

cn 

m 

0 

c 

z 

W 

0 

a 

W 

e 

l2 F 

v 

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0+ 

- 

e 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0+ 

ESTIMATED DISTANCE (nautical miles) 

Figure 3. Distribution of estimated radial distances from ship to dolphin 

schools at the time of initial sightings for a) tuna vessels 

1976-82, b) research vessels 1976-81, and c) research vessels 

1982- 83 . 
39 

c r- 3 4 3 

4.3 

3 

cu 

gs 

3 

src 7 3 

s? 

3 3 

3 

IL 

v ore a0 

cv 0 a +-ai> 

c, u) ni 

I I 

a8 

3 

r- cu -:Iz; 3 3 

m+? a, v) 

3 3 

ra, 

cu(4 

3 

I1 

. * 

a 0 i 0 
40 

F 

% 

3 

e rc 

0 0 OD 

LL 

OD 

e 0 re m 

e 0 

m - r 

r c 

r e 

L L N c P) 0 

u) e 

L 

(0 

rN N 

m (0 
41 

0) 

(D 

L 

IS). 

m 

m N 

A- h d I IC r 

la 

m L I I L L 09) 

N 

N -L 
42 

v) 

0 

0 

* 

0 

0 

c9 

0 

0 

x 

cu 

0 

0 00 

r 0 

0 0 

c9 cu 

0 0 0 0 

Figure 7. Empirically derived distribution of X from bootstrap test of 

Arrow denotes X value of observed 

whether species proportions from tuna and research vessels are 

significantly different. 

tuna vessel vs. research vessel comparison. 
t. 

IA 

- 

u 

m 

a 

.4 

.6 

.4 

.2 

' 

43 

Perpendicular 

Distance 

0 - 

0 0.5 1 .o 1.5 

.2 *4L 

0 

0 

X 

Sighting Cue 

.1 .2 

X 

School Size 

.2 

0 

0 .1 .2 .3 .4 .5 

X 

AL Year 

0 .1 .2 .3 .4 .5 

X 

Sea State 

.2 

0 

0 .05 .10 

.6 

.4 

X 

Season 

Distance From 

Last Sighting 

.4 

.2 

0 

0 .05 .10 .15 .20 

X 

Figure 8. Empirically derived distributions of X from bootstrap test of 

whether species proportions within different strata of the 

indicated factor are significantly different for research vessel 

sightings. Arrows denote observed values for the indicated test. 
44 

.6 Perpendicular 

.4 

Distance 

.2 

0 

0.1 0.2 0.3 

X 

Sighting Cue 

.4 

.2 

0 

0.1 0.2 0.3 0.4 0.5 0.6 

.6 

.4 

.2 

0 

4 

.4 ISeason 

X 

Effort 

0 .001 .002 .003 .004 -005 

X 

Distance From 

Previous Sighting 

0 .1 .2 

.6 

.4 

.2 

0 

0 .05 .10 

X 

Sea State 

.2 

0 

0 .005 .010 .015 .020 .025 

X 

-0 1 .02 .03 

X 

0 .01 .02 .03 .04 .05 

X 

Figure 9. Empirically derived distributions of X from bootstrap test of 

whether species proportions within different strata of the 

indicated factor are significantly different for tuna vessel 

sightings. Arrows denote observed values for the indicated test. 
RECENT TECHNICAL MEMORANDUMS 

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Histopathological manual for monitoring health of striped 

bass in relation to pollutant burdens. 

J.A. WHIPPLE, M. JUNG, R.B. MacFARLANE and R. FISCHER 

(August 1984) 

Hawaiian monk seal population research, Lisianski Island, 

1982. 

H.S. STONE 

(August 1984) 

Interpreting spotted dolphin age distributions. 

J. BARLOW and A.A. HOHN 

(August 1984) 

Observations of the Hawaiian Monk Seal on Laysan Island 

from 1977 through 1980. 

B.W. JOHNSON and P.A. JOHNSON 

(October 1984) 

Hawaiian Monk Seal observations on French Frigate Shoals, 

1980. 

P.A. JOHNSON and B.W. JOHNSON 

(October 1984) 

Estimating dolphin juvenile survival rates from the proportion 

of calves nursing. 

T. POLACHECK 

(October 1984) 

Operational plan for NMFS albacore program. 

R.H. PARRISH, et at. 

(May 1985) 

Albacore fishing and windspeed. 

P.N. SUND 

(June 1985) 

Proceedings of the workshop on the fate and impact 

of marine debris, 27-29, November 1985, Honolulu, Hawaii. 

R.S. SHOMURA and H.O. YOSHIDA (Editors) 

(August 1985) 

The Hawaiian Monk Seal and Green Turtle on 

Necker Island, 1983. 

R.J. MORROW and E.K. BUELNA 

(October 1985)