c 

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NOAA Technical Memorandum NMFS 

SUMMARY REPORT OF THE BOIIIIFUSH 

SUOCK ASSESSMENT WORKSHOP 

PACUFUC RESOURCES 

BBoIerlao Laboratory, Southwest Fisheries center 

Honoolulu, Hawaii 

5-04 December u977 

Richard S. Shomura ( Editor) 

NOA A - TM - NMFS - S W FC - 5 

July 1980 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

Soul h wesl Fisheries Center 
NOAA Technical Memorandum NMFS 

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NOAA Technical Memorandum NMFS 

a- 

* 

This TM series IS used for documenlallon and tlmely comrnunicatlon of preltminary results. lmterlm reports. or 

special purpose inlorrnaflon and have not received cornplele formal review editorial control. or detailed edltlng 

SUMMARV REPORT off THE BOLLFOSH 

SuocK ASSESSMENU WORKSHOP 

RESOURCES 

st Fisheries center 

Richard S. Shomura ( Editor) 

National Marine Fisheries Service 

Southwest Fisheries Center 

Honolulu Laboratory 

Honolulu, Hawaii 96812 

July 1980 

U.S. DEPARTMENT OF COMMERCE 

Philip M. Klutznick, Secretary 

National Oceanic and Atmospheric Administration 

Richard A. Frank, Adminisirator 

National Marine Fisheries Service 

Terry L Leitzell, Assistant Administrator for Fisheries 
iii 

TABLE OF CONTENTS 

Introduction 

Data limitations 

c 

Summary of stock appraisal 

Blue marlin 

Black marlin 

Striped marlin 

Swordfish 

Shortbill spearfish 

Sailfish 

Summary of recommendations 

Statistics 

Res ear ch 

Management 

Literature cited 

Appendix A, Rapporteurs' reports 

Blue marlin, Makaira nigricans 

(Heeny S. H, Yuen and Peter M. Miyake, Rapporteurs) 

Striped marlin, Tetrapturus audax 

(Norman W. Bartoo and Shoji Ueyanagi, Rapporteurs) 

Sailfish, Istiophorus platypterus, and shortbill spearfish, 

Tetrapturus angustirostris 

(James L. Squire and Ziro Suzuki, Rapporteurs) 

Swordfish, Xiphias gladius 

(Gary T. Sakagawa and Robert R. Bell, Rapporteurs) 

Black marlin, Makaira indica 

(Jerry A. Wetherall and Rong-Tszong Yang, Rapporteurs) 

Appendix B, List of participants 

Page 

1 

2 

4 

4 

4 

4 

5 

5 

6 

6 

6 

7 

7 

9 

13 

20 

30 

40 

51 

58 
INTRODUCTION 

The recent extension of national fishery jurisdiction throughout 

the world has resulted in an increased interest in developing fishery 

management agreements, guidelines, and policies. Basic to this development is information on the status of exploited fish stocks. For many 

species, particularly the pelagic species, the dimensions of the resource 

base are unknown, since basic research on population dynamics and the 

collection of adequate fishery statistics have not been accomplished. 

This is certainly the case for the several species of billfishes even 

though they are important targets of commercial and recreational fisheries (Table 1). At the International Billfish Symposium convened in 1972 

at Kailua-Kona, Hawaii, a glaring shortcoming of the virtual absence of 

information on stock assessment or fishery dynamics of billfishes was 

noted (Shomura and Williams 1974, 1975a, 1975b). 

Table 1.--Total Pacific billfish catch (metric tons) by species, 

1952-75. 

~ 

Blue Striped Sailfish and Black 

Year marlin marlin Swordfish spearfish marlin Total 

x 

1952 

1953 

1954 

1955 

1956 

1957 

1958 

1959 

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

1975 

15,525 

17,250 

10,519 

24,190 

18,770 

23,500 

22,106 

20,275 

18,155 

26,581 

30,743 

31,344 

23,233 

18,885 

18 588 

17,233 

15,283 

17,427 

20,115 

13,342 

15,300 

17,285 

15,594 

12,546 

4,992 

3,789 

7,256 

7,075 

7,724 

7,150 

8,999 

8,986 

7,362 

10,084 

13,685 

16,944 

23,480 

24,017 

20,967 

22,050 

27,143 

21,706 

24,221 

24,264 

14,541 

15,407 

14,669 

16,279 

11,339 

11,689 

13,392 

16,485 

12,584 

16,243 

21,341 

19,663 

23,409 

24,286 

14,604 

14,133 

10,112 

12,949 

14,601 

15,649 

15,230 

18,934 

15,727 

11,037 

11,029 

13,791 

11,664 

13,376 

2,000 

3,300 

2,400 

3,300 

3,200 

2,800 

3,400 

3,400 

5,000 

4,800 

6,800 

7,900 

6,100 

12 800 

11,100 

11,800 

12,500 

12 800 

9,000 

8,100 

8,600 

8,700 

7,100 

5,500 

1,806 35,662 

3,188 39,216 

5,370 38,937 

5,379 56,429 

6,466 48,744 

6,376 56,069 

4,548 60,394 

3,081 55,405 

2,721 56,647 

3,170 68,921 

4,066 69,898 

3,180 73,501 

2,805 65,730 

4,039 72,690 

3,729 68,985 

2,836 69,568 

2,362 72,518 

2,546 73,413 

2,207 71,270 

2,674 59,417 

3,424 52,894 

3,720 58,903 

3,048 52,075 

2,796 50,497 
L 7

In early 1977 the Honolulu Laboratory, Southwest Fisheries Center, 

National Marine Fisheries Service developed plans jointly with the Western 

Pacific Regional Fishery Management Council (WPRFMC) to hold a Pacific 

Billfish Stock Assessment Workshop. 

to include the Atlantic stocks. Its objective was to produce a report 

containing a scienti€ic assessment of the status of billfish stocks in the 

Pacific and Atlantic along with a summary of appropriate background information, supporting analyses, and recommendations. The workshop was held 

at the Honolulu Laboratory in December 1977 and consisted of two parts, 

a Pacific section (5-9 December), which reviewed the Pacific billfish 

stocks, and an Atlantic section (12-14 December), which treated the Atlantic billfish stocks. The Pacific workshop covered the six species of 

Pacific billfishes: blue marlin, Makaira nigricans; black marlin, - M. 

indica; striped marlin, Tetrapturus audax; shortbill spearfish, T. 

angustirostris; sailfish, .- Istioe platypterus; swordfish, Xiphias 

gladius. 

The workshop was subsequently expanded 

Since by far the greater part of the exploitation of the Pacific 

billfish resources is carried on by foreign fishexmen, and consequently 

foreign governments possess most of the data relevant to their management, 

the success of the workshop required the joint participation of scientists 

from the major billfish fishing nattons. Scientists from the Honolulu, 

La Jolla, and Miami Laboratories of the National Marine Fisheries Service, 

the California Department of Fish and Game, the Far Seas Fisheries Research 

Laboratory (Shimizu, Japan), National Taiwan University (Taipei, Taiwan), 

Fisheries Research & Development Agency (Pusan, Korea), and the International Commission for the Conservation of Atlantic Tunas were invited 

to participate in the workshop. The WPRFMC sponsored the participation 

of the foreign scientists. The Council has direct interest in the results 

of the workshop, since it is presently developing a management plan for 

the Pacific billfishes. 

This report covers the Pacific section of the workshop including 

brief summaries of the Pacific billfish stock appraisals and recommendations for improvement of fishery statistics, research, and management. 

These are followed by the several rapporteurs' reports (Appendix A), 

which provide detailed discussions of the stock assessments. Appendix B 

lists the participants. 

DATA LIMI TAT IONS 

A complete understanding of the effects of fishing on fish stock 

productivity and catch requires a knowledge of growth rates, mortality 

rates, reproductive rates, and other vital determinants of population 

dynamics. Unfortunately, in the case of Pacific billfishes such detailed 

information has not been acquired. 

data on size composition and some estimates of growth rates, the only 

kinds of information available for stock assessment purposes are statistics on nominal fishing effort and catch. Under these data limitations 

the billfish stocks were assessed using catch per unit effort (CPUE) and 

Except for a very limited amount of 
3 

.... 

effort trends, as well as the surplus production approach popularized by 

Schaefer (1954, 1957) in the 1950’s and improved most recently by Fox 

(1975). 

In using the prqduction model we made two fundamental assumptions 

concerning the catch and effort data: 

(1) the CPUE is proportional to average stock abundance, with the 

ratio of CPUE to abundance remaining constant over the period of analysis, 

and 

(2) the total catch is known. 

Violations of these assumptions were suspected for certain billfish stocks, 

and known to occur in others. In the latter cases no attempt was made to 

fit a production model or to estimate a maximum sustainable yield (MSY). 

With respect to CPUE, the statistic used in all analyses was the 

catch per 1,000 hooks fished in the Japanese pelagic longline fishery, 

a fishery which generally concentrates on tunas and harvests billfishes 

only incidentally. Changes in the construction or deployment of the 

longline gear, shifts in fishing strategy or target species, and changes 

in availability of the fish to the gear are some of the factors which may 

alter the ratio of CPUE to average abundance. For example, in the North 

Pacific, a reduction in nighttime longlining activity targeted specifically on swordfish is almost certainly responsible for a sharp drop in 

the average swordfish CPUE in that area since the early 1960’s. 

assessment of the North Pacific swordfish stock is therefore complicated, 

because the effects of the change in fishing strategy on fhe ratio of 

CPUE to abundance are unknown. Similar problems may exist in the assessment of other species. 

The 

In the case of total catch, there are generally reliable figures in 

numbers of fish for the Japanese tuna longline fleet, which accounts for 

most of the overall harvest and dominates the catch statistics of most 

billfish species. 

shortbill spearfish, which is reported as a combined total in the longline statistics. In addition, there are serious problems in estimating 

the total weight of billfishes taken in the inshore or coastal fisheries 

which use other kinds of gear, e.g., gill nets, and in determining the 

total catch of other major distant-water longline fleets, particularly 

the catch of Korean vessels. 

the magnitude of bias may vary from year to year, creating serious problems in interpretation of catch-effort relationships. 

An exception is the Japanese catch of sailfish and 

Where biased catch estimates are suspected, 

Aside from the major assumptions about the catch and effort data 

there are several other important conditions which must be met if the 

production model analysis is to be valid. The most important of these 

is that the data refer to a single stock of the species under consideration. Stock units for the Pacific billfish populations were selected on 

the basis of limited evidence concerning larval distribution, seasonality 
4 

and locations of spawning, catch rate distribution, and tag return 

pattern. 

remains to be established. 

The validity of the stock boundaries assumed for this r'eport 

Other critical assumptions of the production model are discussed 

in detail by Fox (1975). When these are considered along with the ones 

discussed above, it is clear that the production model analysis and the 

resulting estimate of MSY can give at best only very rough approximations 

on the status of a fish stock and the effects of fishing effort on yield. 

The stock appraisals summarized below and discussed in greater detail in 

the rapporteurs' reports should be judged in this context. 

SUMMARY OF STOCK APPRAISAL 

Blue Marlin 

A single Pacific-wide stock of blue marlin is assumed. Total harvest 

Catch per unit effort has decreased 

in 1975 was approximately 12,500 metric tons (mt), of which about 80% was 

taken by the longline fleet of Japan. 

steadily since the early 1950'~~ while total effective fishing effort has 

increased. The production model analysis gives an MSY estimate of about 

22,000 mt, which is associated with an effective fishing effort equal to 

about 50% of the 1975 total effective effort. The Pacific blue marlin 

stock is judged to be'overfished. 

Black Marlin 

The stock structure of black marlin is unknown, but the restricted 

coastal distribution of the species and the occurrence of isolated areas 

of high catch rates suggest the possibility of more than one stock in the 

Pacific. 

marlin between the western Pacific and the eastern Indian Ocean occurs. 

The total Pacific catch in recent years has been estimated at around 

3,000 mt. Stock assessment is complicated by underestimation of total 

catches, particularly those made by the Taiwan fleet. For this reason 

no estimate of MSY is available; however, sharply declining catch rates 

during the 1950's and a more gradual reduction of apparent abundance since 

the early 1960's suggest that increased fishing effort, would, at best, 

produce only a small increase in average catch. Until better estimates 

of total catch are obtained, the status of black marlin harvests cannot 

be reliably ascertained. 

Furthermore, there is a strong likelihood that movement of black 

Striped Marlin 

Striped marlin total catches increased steadily from nearly 5,000 mt 

in 1952 to 24,000 mt in 1965. From 1965 to the early 1970'~~ the catches 

remained in the 20,000 to 27,000 mt range. In 1972 striped marlin catches 

dropped to 14,500 mt and remained between 14,500 and 16,300 mt through 

1975. 
5 

The stock structure of the Pacific striped marlin is unclear; however, 

evidence based on distribution of catch rates and other factors suggests 

the population could consist of either (1) separate north and south stocks 

or (2) a single unit stock for the entire Pacific Ocean. 

Estimated MSY is 24,000 mt in the case of a single Pacific-wide 

stock. Current assessments indicate that the stock(s) of Pacific striped 

marlin is (are) in good condition and not in need of restrictive managemen t . 

Swordfish 

Most of the catch of swordfish from the Pacific Ocean is landed by 

the Japanese longline fleet and is made in the northwestern Pacific. 

The total Pacific catch increased from 11,300 mt in 1952 to a record high 

of 24,300 mt in 1961. The catch then declined abruptly to about 14,600 mt 

in 1962 and has leveled off at an average of 14,000 mt since 1962. 

The stock structure of the Pacific swordfish population is not 

clearly understood. Current opinion is that the population consists 

either of a single Pacific-wide stock or of three separate stocks, the 

latter with centers of concentration in the northwestern, southwestern, 

and eastern Pacific. 

sis assuming a single Pacific-wide stock is 20,000 mt, compared to the 

current catch level of about 14,000 mt. Since present fishing effort is 

about 20% below the effort required to take the MSY, the fishery does not 

appear to be overexploiting the stock and the stock appears to be in good 

condition. 

The MSY calculated from the production model analyNo individual estimates of MSY are available in the case of three 

separate stocks. 

Shortbill Spearfish 

The major longline fisheries report the catches of shortbill spearfish 

together with catches of sailfish. Very little of the combined catch, 

however, consists of shortbill spearfish. Since the shortbill spearfish 

commands the lowest price among the billfishes caught in longline fisheries, 

catches of this species are not consistently reported. The amount of shortbill spearfish reported is probably an underestimate of the actual catch. 

The stock structure of shortbill spearfish is not known; however, 

the catch rates are relatively high around lat. 20°N and 20°S and low at 

the Equator, thus suggesting a possible North Pacific stock and a South 

Pacific stock. 

Estimates of MSY for the stock(s) of shortbill spearfish are not 

available due to the unreliable catch statistics. Estimated catch rates of 

this species from longline data suggest that the stocks are currently at 

a relatively high level of abundance and the species is probably underutilized. 
6 

Sailfish 

Although the catches of shortbill spearfish and sailfish are reported 

combined, the bulk of the catch consists of sailfish. The estimated 

sailfish-spearfish catch increased gradually from 2,000 mt in 1952 to 

6,100 mt in 1964. It then increased markedly to a record high level of 

about 12,800 mt in the 1965-69 period. From 1970 through 1975 the catch 

declined to about 5,500 mt. 

Based on distribution of catch rates, the sailfish in the Pacific 

is assumed to consist of two stocks--an eastern Pacific stock and a 

western Pacific stock. In the western Pacific the catch rate of sailfish 

has shown a decline since 1959. The 1975 catch rate of two fish per 

10,000 hooks is the lowest average rate recorded for the western Pacific 

fishery. The CPUE for the eastern Pacific fishery increased sharply 

between 1960 and 1965 to about 200 fish per 10,000 hooks, fluctuating 

downward to about 110 fish per 10,000 hooks in 1975. 

Estimation of MSY for sailfish was not attempted because there is 

yet no reliable method of separating the combined catch by species. 

patterns in catch rates and associated nominal fishing effort, however, 

suggest that the sailfish stock(s) is (are) not in bad shape. 

The 

SUMMARY OF RECOMMENDATIONS 

Statistics 

The statistics needed to accurately assess the condition of a fish 

stock and to evaluate the effects of fishing include estimates of total 

catch, catch and effort, and data on the size, sex, and age composition 

of the catch. 

of the longline fishery, required data are virtually nonexisting for 

billfishes. Even with the available catch and effort data several shortcomings were noted at the workshop. These were (1) incomplete catch and 

effort records for certain commercial fisheries, e.g., the Korean longline 

fishery; (2) the virtual absence of recreational billfish catch and effort 

data, e.g., the Australian and United States recreational fisheries; (3) 

the pooling of sailfish and shortbill spearfish catches in the basic logbooks maintained by the Japanese longline fleet; and (4) the reporting 

of catch in different units, e.g., round weight, dressed weight, or number. 

Except for catch and effort statistics from some segments 

The workshop recommended that all nations with billfish fisheries be 

urged to establish new sampling programs and procedures to insure the 

collection of adequate statistics including (1) total catch by species, 

gear, type of fishing operation, and ocean region; (2) total nominal 

effort by gear, type of fishtng operation, and ocean region; (3) CPUE by 

effort, small area-time strata, gear, and type of fishing operations; 

and (4) size and sex composition of the catches by species and by small 

area-time strata. 
7 

Res ear c h 

Appraisals of fish stock conditions rely on basic biological information and adequate statistics describing the fisheries over several years. 

For billfishes, such basic information and data are not adequate for comprehensive stock appraisals. 

based on catch and effort data from the Japanese longline fishery and 

estimates of Pacific-wide catches. 

only tentative assessments of the various billfish stocks. These assessments were based on assumed stock structures, and computed measures of 

effective fishing effort, a statistic which is assumed to be proportional 

to fishing mortality rates. These assumptions are difficult to test and 

verify because they require collections of extensive and detailed data, 

or long and expensive experimentation. It is possible, however, to use 

computer simulation models to examine the sensitivity of stock assessment 

conclusions and management advice to changes in assumptions, e.g., doubling 

the effective fishing effort. The cost of this kind of analysis is expected 

to be modest and should provide valuable guidance for research planning. 

The present assessment of billfish stocks is 

The lack of adequate data permitted 

The workshop recommended that countries be urged to support modeling 

and computer simulation analyses as a high priority research task. 

Another high priority research task identified at the workshop was 

the need to define the stock structure of the various species of billfishes. 

Proper assessment and management of the billfish resources will require 

some understanding of stock structure. While tagging programs provide 

some of the necessary information, the low catch rates of commercial and 

recreational fisheries suggest that other techniques are probably more 

suitable, e.g., immunogenetic methods. 

The workshop also recognized the need for the application of other 

analyses to the billfish stocks, e.g., yield-per-recruit analysis. Since 

these approaches require age and growth information the workshop recommended that research be undertaken to determine the age of billfishes and 

to establish age-size relations. 

The workshop noted that assessments of the billfish resources could 

be improved by conducting a further detailed study of the longline fishery and a more complete treatment of other fisheries for billfishes, 

including the Japanese gill net fishery. 

was noted that changes in fishing method and strategy, such as the recent 

increased effort by deep-fishing longline gear and the reduction in the 

longline fishery by swordfish, could have a marked influence in the computation of effective fishing effort. 

countries having access to extensive historical data undertake studies 

to define these changes and their relation to effective fishing effort. 

For the longline fishery it 

The workshop recommended that 

Management 

Sophisticated management advice for the Pacific billfish fisheries 

is difficult to formulate at this time because of (1) the lack of adequate 
8 

data needed to fully understand the fish stocks and fisheries and (2) the 

absence of effective international arrangements for conservation of highly 

migratory species. Production model analyses of available data, however, 

provide a basis for tentative management advice. 

The available data on the Pacific blue marlin stock suggest that this 

species is overfished. Whether the overfished condition is due to recruitment overfishing or yield-per-recruit overfishing is not known. If the 

condition is caused by recruitment overfishing, the situation is probably 

very serious and appropriate action should be taken to provide for additional escapement as a means of increasing the spawning stock. 

other hand, the condition is caused by yield-per-recruit overfishing, the 

situation is not as serious, but restrictions on effort and/or minimum 

size at capture would be required to improve the average yield. 

If, on the 

The stocks of Pacific striped marlin and swordfish appear to be 

exploited at levels close to estimated MSY. Nevertheless, the stocks 

appear to be in good condition and from a biological viewpoint the fisheries are not in need of restrictive management. However, these species 

should be monitored closely for signs of overfishing. 

The status of the stocks of black marlin, sailfish, and shortbill 

spearfish is less certain. It is concelvable that a detailed reassessment of historical data may provide the basis for separating the combined 

sailfish-shortbill spearfish catch data, thus permitting appropriate production model analyses to be undertaken. Similarly, improved estimates 

of total catch may lead to better assessment of the black marlin resources. 

In the meantime no restrictive management is deemed necessary from a biological viewpoint. 

With respect to management institutions, the widespread distribution 

and migratory tendencies of the billfishes suggest that effective management can only be achieved by a broad-based management program, covering 

the entire range of the stocks. To date, a management mechanism of this 

nature does not exist in the Pacific. 

The workshop recommended that countries harvesting billfi s in the 

Pacific support continuing efforts to assess the stocks and assist in formulating management options which will lead to optimal utilization of the 

billfish resources. 
9 

LITERATURE CITED 

... 

c 

CADDY, J. F. 

1977. Some approaches to elucidation of the dynamics of swordfish 

(Xiphias gladius) populations. Biol. Stn., St. Andrews, N.B., Can., 

Fish. Mar. Serv., MS Rep. 1439, 10 p. 

DE SYLVA, D. P. 

1957. Studies on the age and growth of the Atlantic sailfish, 

Istiophorus americanus (Cuvier), using length-frequency curves. 

Bull. Mar. Sci. Gulf Caribb. 7:l-20. , 

ELDRIDGE, M. B., and P. G. WARES. 

1974. Some biological observations of billfishes taken in the 

eastern Pacific Ocean, 1967-1970. In R. S. Shomura and F. 

Williams (editors) , Proceedings of the International Billfish 

Symposium, Kailua-Kona, Hawaii, 9-12 August 1972, Part 2. Review 

and Contributed Papers, p. 89-101. U.S. Dep. Comer., NOM Tech. 

Rep. NMFS SSRF-675. 

FOX, W. M., JR. 

1975. Fitting the generalized stock production model by least-squares 

and equilibrium approximation. Fish. Bull., U.S. 73:23-37. 

a. 

I. 

HOW, M., and T. KAMIMURA. 

1958. A population study on the so-called makajiki (striped marlin) 

of both northern and southern hemispheres of the Pacific. 11. 

Fishing conditions in the southern hemisphere. [In Jpn., Engl. 

synop.] Rep. Nankai Reg. Fish. Res. Lab. 8:12-21. 

HOWARD J. K., and S. UEYANAGI. 

1965. Distribution and relative abundance of billfishes (Istiophoridae) of the Pacific Ocean. Stud. Trop. Oceanogr., Inst. Mar. 

Sci., Univ. Miami 2, 134 p. 

JOLLEY, J. W., JR. 

1977. The biology and fishery of Atlantic sailfish Istiophorus 

platypterus, from southeast Florida. Fla. Mar. Res. Publ. (28), 

31 p. 

KAMIMlTRA, T., and M. HOW. 

1958. A population study of the so-called makajiki (striped marlin) 

of both northern and southern hemispheres of the Pacific. I. 

Comparison of external characters. [In Jpn., Engl. synop.] Rep. 

Nankai Reg. Fish. Res. Lab. 8:l-11. 

KOTO, T. 

1963. Some considerations on the growth of marlins, using size 

frequencies in commercial catches. 111. Attempts to estimate the 

growth of striped marlin, Tetrapturus audax (Philippi) in the 

western North Pacific Ocean. [In Jpn., Engl. synop.] Rep. Nankai 

Reg. Fish. Res. Lab. 17:63-85. 
10 

KOTO, T,, and K. KODAMA. 

1962a. Some considerations on the growth of marlins, using sizefrequencies in commercial catches. I. Attempts to estimate the 

growth of sailfish. [In Jpn., Engl. abstr.] Rep. Nankai Reg. 

Fish. Res. Lab. 15:97-108. 

1962b. Some considerations on the growth of marlins, using size 

frequencies in commercial catches. 11. Attempts to estimate the 

growth of so called white marlin, Marlina marlina (J. and H.). 

[In Jpn., Engl. abstr.] Rep. Nankai Reg. Fish. Res. Lab. 15: 

109-126. 

KUME, S., and J. JOSEPH. 

1969a. The Japanese longline fishery for tunas and billfishes in 

the eastern Pacific Ocean east of 13OoW, 1964-1966. [In Engl. 

and Span.] Inter-Am. Trop. Tuna Comm., Bull. 13:275-418. 

1969b. Size composition and sexual maturity of billfish caught by 

the Japanese longline fishery in the Pacific Ocean east of 130"W. 

Bull. Far Seas Fish. Res. Lab. (Shimizu) 2:115-162. 

MATHER, F. J., 111, J. M. MASON, JR., and H. L. CLARK. 

1974. Migrations of white marlin and blue marlin in the western 

North Atlantic Ocean--tagging results since May, 1970. R. S. 

Shomura and F. Williams (editors), Proceedings of the International 

Billfish Symposium, Kailua-Kona, Hawaii, 9-12 August 1972, Part 2. 

Review and Contributed Papers, p. 211-225. U.S. Dep. Commer., 

NOAA Tech. Rep. NMFS SSRF-675. 

SCHAEFER, M. B. 

1954. Some aspects of the dynamics of populations important to the 

management of the commercial marine fisheries. Inter-Am. Trop. 

Tuna Comm. Bull. 1:25-56. 

1957. A study of the dynamics of the fishery for yellowfin tuna in 

the eastern tropical Pacific Ocean. [In Engl. and Span.] InterAm. Trop. Tuna com. Bull. 2:245-285. 

SHOMURA, R. S., and F. WILLIAMS (editors). 

1974. Proceedings of the International Billfish Symposium, KailuaKona, Hawaii, 9-12 August 1972, Part 2. Review and Contributed 

Papers. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-675, 335 p. 

1975a. Proceedings of the International Billfish Symposium, KailuaKona, Hawaii, 9-12 August 1972, Part 1. Report of the Symposium. 

U.S. Dep. Commer., NOM Tech. Rep. NMFS SSRF-675, 33 p. 

1975b. Proceedings of the International Billfish Symposium, KailuaKona, Hawaii, 9-12 August 1972, Part 3. Species Synopses. U.S. 

Dep. Commer., NOAA Tech. Rep. NMFS SSRF-675, 159 p. 
c 

11 

_- SKILLMAN, R. A., and M. Y. Y. YONG. 

1974. Length-weight relationships for six species of billffshes in 

the central Pacific Ocean. In R. S. Shomura and F. Williams 

(editors) , Proceedings of thTInternationa1 Billfish Symposium, 

Kailua-Kona, Hawaii, 9-12 August 1972, Part 2. Review and Contributed Papers, p. 126-137. U.S. Dep. Comer., NOAA Tech. Rep. 

NMFS SSRF-675. 

1976. Von Bertalanffy growth curves for striped marlin, Tetrapturus 

audax, and blue marlin, Makaira nigricans, in the central North 

Pacific Ocean. Fish. Bull., U.S. 74:553-566. 

WARES, P. G., and G. T. SAKAGAWA. 

1974. Some morphometrics of billfishes from the eastern Pacific 

Ocean. In R. S. Shomura and F. Williams (editors), Proceedings of 

the International Billfish Symposium, Kailua-Kona, Hawaii, 9-12 

August 1972, Part 2. Review and Contributed Papers, p. 107-120. 

U.S. Dep. Comer., NOAA Tech. Rep. NMFS SSRF-675. 

YABE, H., S. UEYANAGI, S. KIKAWA, and H. WATANABE. 

1959. Study on the life-history of the sword-fish Xiphias gladius 

Linnaeus. Rep. Nankai Reg. Fish. Res. Lab. 10:107-150. 

YOSHIDA, H. 0. 

1974. Landings of billfishes in the Hawaiian longline fishery. In 

R. S. Shomura and F. Williams (editors), Proceedings of the International Billfish Symposium, Kailua-Kona, Hawaii, 9-12 August 1972, 

Part 2. Review and Contributed Papers, p. 297-301. U.S. Dep. 

Commer., NOAA Tech. Rep. NMFS SSRF-675. 
13 

APPENDIX A 

RAPPORTEURS' REPORTS 

BLUE MARLIN, MAKAIRA NIGRICANS 

.- 

Heeny S. H. Yuen and Peter M. Miyake, Rapporteurs 

REVIEW OF FISHERIES DATA 

The blue marlin, Makaira nigricans, has been characterized as the 

predominant marlin of the central tropical Pacific. 

distributed in the Pacific Ocean: from the American to the Asiatic Continents between approximately lat. 45'N and 45's (Appendix Figure 1). 

Blue marlin are taken primarily by longlines and small numbers are taken 

by gill nets and harpoons. Japan, Taiwan, and the Republic of Korea have 

large Pacif ic-wide longline fisheries that take blue marlin. Blue marlin 

are caught by recreational fishermen in Hawaii, from Mexico to Ecuador in 

the eastern Pacific, and from Australia to Japan in the western Pacific. 

They are widely 

Catch. Trends 

The total annual Pacific catch of blue marlin from 1952 to 1975 rose 

irregularly and reached a peak of 31,300 mt in 1963 and declined irregularly thereafter (Appendix Table 1; Appendix Figure 2). 

have been consistently greater in the North Pacific than in the South 

Pacific; the North Pacific catch in 1975 was 84% of the Pacific total. 

The annual catches 

Effort Trends 

Effective fishing effort increased from about 50 million hooks in 

1952 to about 260 million hooks in 1963 and fluctuated around 200 million 

hooks from 1964 to 1975 (Appendix Figure 3). 

Catch Rate Trends 

Catch per effort steadily declined from about 3.0 fish per 1,000 

hooks in 1952 to about 0.5 fish per 1,000 hooks in 1975 (Appendix Figure 

3). The 1975 CPUE was the lowest value recorded for blue marlin. 

STOCK STRUCTURE 4.. 

Blue marlin appear to comprise a single equatorially centered stock 

in the Pacific. Concentrations of blue marlin alternately appear at 

higher latitudes on both sides of the Equator during the respective summer 

periods. Evidence for a unit stock assumption is the apparently single, 

large spawning area in the western Pacific, including areas of high spawning densities in the west and declining densities eastward. As is true of 

the other billfishes, confirmation of the blue marlin stock structure 

hypothesis is needed. 

c 
14 
15 

Appendix Tab,le 1. --Blue marlin catches (metric tons) 

by countries for the Pacific Ocean, 1952-75. 

Repu bl i c 

Year Japan Taiwan of Korea Others Total 

1952 

1953 

1954 

1955 

1956 

1957 

1958 

1959 

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

1975 

15,525 

17,250 

10,253 

23,590 

18,136 

23,030 

21,712 

19,908 

17,825 

26,267 

29,983 

29,434 

21,323 

16,675 

16,156 

13,944 

12,300 

14,415 

16,976 

9,932 

11,760 

13,252 

12,313 

9,735 

266 

600 

634 

470 

394 

367 

330 

314 

760 

1,910 

1,910 

1,910 

1,910 

2,428 

2,562 

2,371 

2,481 

2,757 

2,787 

3,280 

2,410 

2,229 

222 

461 

221 

441 

453 

453 

453 

453 

453 

453 

300 

300 

4 00 

200 

200 

200 

200 

200 

300 

418 

129 

15,525 

17,250 

10,519 

24,190 

18,770 

23,500 

22,106 

20,275 

18,155 

26,581 

30,743 

31,344 

23,233 

18,885 

18,888 

17,233 

15,283 

17,427 

20,115 

13,342 

15,300 

17,285 

15,594 

12,546 

POPULATION PARAMETERS 

The available population parameters are shown in Appendix Table 5. 

Like the other billfishes, basic data on mortality rates, age and growth, 

fecundity, etc., are tentative and need to be improved. The inability to 

confirm age estimates of blue marlin has hampered stock assessment work. 

The existing growth equation should be ve.rified so that age composition 

of the catch can be computed when length composition data become available. 

STOCK ASSESSMENT 

Pacific-wtde catch and effort data (Appendix Table 1) were used to 

assess the current status of the assumed single blue marlin stock. 

n 
16 

35 

30 

25 

2c 

15 

IC 

f 

C 

llllllll111Illllll111111 

BLUE MARLIN 

11111111111111111 II1IIII 

1955 1960 1965 1970 l97t 

YEAR 

Appendix Figure 2.--Blue marlin catch in the Pacific, 1952-75. 

The relation between CPUE and effective effort trends (Appendix 

Figure 3) provides indications of the condition of the stock. The CPUE 

from 1952 to 1975 steadily declined from 3 fish per 1,000 hooks in 1952 

to 0.5 fish per 1,000 hooks in 1975, including only minor fluctuations. 

Over the period from 1952 to 1963, effort rose steadily, increasing by a 

factor of 4. Subsequently, a relatively constant, high level of effective 

effort was evident from 1964 to 1975. The steady decline in CPUE over the 

last 10 years in the presence of a fairly constant effort indicates a 

potential problem with the stock. 

A production model was fitted to the 1952 to 1975 data for the entire 

Pacific (Appendix Figure 4). 

per year at an optimum effort level of 5.5 x lo5 hooks per 5' square which is 

approximately equivalent to a total effective effort of 142 million hooks. 

The 1975 catch of 12,500 mt was taken by an effort of 10 x lo5 hooks per 

5" square or approximately 215 million effective hooks. The model appears 

to fit the data quite well. 

The results project an MSY of about 22,000 mt 
I. 7 

. 

111111111111111111111111 

BLUE MARLIN 

CATCH RATE 

0.J 

\ ,EFFECTIVE EFFORT 

1111111I111111111IIII11I 

1955 I960 1965 I970 I97C 

YEAR 

400 

300 

200 

IO0 

0 

Appendix Figure 3.--Catch rate and effective fishing effort for 

blue marlin in the Pacific, 1952-75. 

Although it is not possible to perform additional analyses to estimate 

yield-per-recruit or recruitment indices, the combined evidence of CPUE and 

effort trends and production model analysis suggests that the blue marlin 

stock is being substantially overfished. This overfishing apparently began 

in the early 1960's and has continued through 1975. 

OVERALL STOCK APPRAISAL 

The evidence of declining CPUE and the result of the production model 

analysis suggests that the blue marlin stock is being overfished. The 

present effort is almost twice that needed for MSY. 

RECOMMENDATIONS 

Statistics 

To confirm the current appraisal of the blue marlin stock, additional 

basic data must be obtained. Length-composition samples by sex for current 

catches should be collected, and historical size-composition data should be 

analyzed. 'Additional catch and effort data should be collected from fleets 

with presently low coverage rates. 
18 

361 

32 - 

28 - 

24 - 

20 - 

16 - 

12 - 

BLUE MARLIN 

m = 1.87 

k=5 

% 

60 

g.,, 4 

68 

75 

\ 

\ 

/ \ 

/ \ 

\ 

\ 

\ 

\ 

8- 

/ \ 

4-/ \ \ 

\ / 

/ 

I I I I I I I I I I \ 

0 I2 3 4 5+6 7 8 9 IO I1 12 13 

Appendix Figure 4.--Relation between catch of blue marlin and 

effective fishing effort. 

on the production model. 

The equilibrium yield curve is based 

Research 

The potentially serious condition of the blue marlin stock suggests 

that additional analyses to confirm the current appraisals are needed. 

The available age-growth results need to be confirmed. 

and recruitment indices are needed. 

take into account differential catch rates and growth by sex. 

Yield-per-recruit 

These analyses should, if possible, 

Manag emen t 

The production model analysis indicates that the Pacific blue marlin 

stock has been substantially overfished since the early 1960's. 

tive fishing effort increased from 1952 to 1962, then essentially leveled 

off during 1963 to 1975; however, effective fishing effort in 1975 was at 

the highest level since the beginning of the fishery in 1952 and was almost 

twice the computed optimum effort. 

yield has been declining since 1963 and CPUF has been declining since 1952. 

EffecRelative to these effort trends, total 
19 

.- 

a 

The total yield obtained in 1975 from this level of effort was the 

second lowest recorded. Although information on stzck-recruitment relations is not presently available. for blue marlin, it: seems clear that 

continued fishing at high I.evels will continue to reduce the abundance 

of the stock and a recruitment failure will become n distinct possibility. 

These warning signs warrant the serious consideration of some form 

of management for blue marlin. In view of the apparent seriousness of 

the situation, it was recommended that the monitoring of the status of 

blue marlin in the Pacific be given the highest possible priority in 

billfish research. 

x 
20 

STRIPED MARLIN, TETRAPTURUS AUDAX 

Norman W. Bartoo and Shoji Ueyanagi, Rapporteurs 

REVIEW OF FISHERIES DATA 

Striped marlin, Tetrapturus -3 audax are widely distributed in the 

Pacific Ocean between lat. 50°N and 50’s. 

of striped marlin indicate 

North and South Pacific which merge in the eastern Pacific to form a 

horseshoe-shaped pattern of high density (Appendix Figure 5). 

The tuna longline catch rates 

bands of relatively high density across the 

Striped marlin are caught in the Pacific tuna longline fisheries of 

Japan, Republic of Korea, and Taiwan, which harvested a combined total 

catch ranging between 14,000 and 16,000 mt annually in recent years 

(Appendix Table 2). The catch of these three countries accounts for most 

of the Pacific striped marlin harvest. In the central North Pacific 

striped marlin are caught by Hawaiian-based longliners and trollers 

(including sport fishing boats). The Hawaiian catch is small, once 

amounting to about 200 mt annually; in recent years it has amounted to 

only about 50 mt. 

Gill nets are also used to catch striped marlin and since 1973 the 

drift-gill net catches off Japan have increased significantly. 

3,000 mt or approximately one-third of the total catch from the North 

Pacific is landed annually by this fishery. 

More than 

Small amounts of striped marlin are caught by recreational fishermen 

off California. Estimates indicate an annual catch averaging 40 mt. Off 

Mexico and Central America, striped marlin are also taken by recreational 

fishermen. The total catch is not known but may be as high as 200 mt per 

year. 

Catch Trends 

The Pacific-wide catch of striped marlin (Japan, Taiwan, Republic of 

Korea, and United States combined) rose steadily from approximately 5,000 

mt in 1952 to 24,000 mt in 1965 (Appendix Table 2; Appendix Figure 6). 

From 1965 to 1971 the catch fluctuated between 21,000 and 27,100 mt. In 

1972 the catch abruptly dropped to 14,500 mt and remained between 14,500 

and 16,300 mt through 1975. 

Catches of striped marlin from the North Pacific area contributed 

most to the Pacific-wide totals. The North Pacific catch increased slowly 

from 1952 through 1963, rose markedly to a peak of 21,000 mt in 1968, and 

since then fluctuated between 9,000 and 18,000 mt (Appendix Figure 6). 

Catches from 1973 through 1975 remained almost constant at near 12,000 mt 

per year. 
21 
22 

Appendix Table 2.--Striped marlin catches (metric tons) 

by countries in the Pacific Ocean; 1952-75. 

~ 

Republic United 

Year Japan Taiwan of Korea States Total 

1952 

1953 

1954 

1955 

1956 

f957 

1958 

1959 

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

197 5 

4,992 

3,789 

7 , 208 

6,927 

7 , 526 

6,944 

8,788 

7,242 

9,922 

13,359 

16,347 

22 , 893 

19,830 

16 , 410 

18,109 

22,103 

19,564 

13,344 

14,122 

13 , 641 

15 , 254 

a, 803 

16 , a13 

19 , 099 

48 

14 8 

198 

206 

128 

108 

58 

104 

242 

5 00 

5 00 

4 , 100 

4 , 400 

3 , 711 

4 , 766 

4 , 589 

4,335 

4,923 

961 

1 , 079 

825 

812 

70 

143 

93 

159 

164 

164 

164 

164 

164 

164 

83 

75 

62 

58 

84 

97 

87 

87 

87 

181 

145 

158 

78 

72 

42 

39 

49 

a7 

4 , 992 

3,789 

7 , 256 

7 , 075 

7 , 724 

7 , 150 

'8,999 

8,986 

7 , 362 

10 , 084 

13 , 685 

16 , 944 

23 , 480 

24 , 017 

20,967 

22 , 050 

27 , 143 

21,706 

24 , 221 

24 , 264 

14 , 541 

15 , 407 

14 , 669 

16,279 

Catches of striped marlin from the South Pacific area showed a 

similar trend but with less fluctuation than in the North Pacific. The 

catch rose from a few tons in 1952 to a peak of 10,000 mt in 1963, dropped 

to 6,500 mt in 1964 and began a slow decline to a low of 4,000 mt in 1975 

(Appendix Figure 6). 

nearly constant at 4,000 mt. 

Annual catches from 1973 through 1975 remained 

Effort Trends 

Total effective fishing effort for the entire Pacific (Appendix 

Figure 7) showed an increasing trend from 1952 through 1964. 

the trend has been relatively flat and fishing effort has been fluctuating 

between about 200 million and 300 million hooks. 

Since then 

Effective fishing effort in the North Pacific increased from 40 

million hooks in 1952 to 180 million hooks in 1964, then declined irregularly to 90 million hooks in 1975 (Appendix Figure 7). Effective fishing 
23 

I3( 

2: 

2c 

IE 

IC 

5 

0 

- PACIFIC-WIDE 

Appendix Figure 6.--Catches of striped marlin in the Pacific, 1952-75. 
24 

YEAR 

Appendix Figure 7.--Catch rates and effective fishing effort 

for striped marlin in the Pacific, 1952-75. 

in the South Pacific showed a modest increase between 1952 and 

and a substantial increase by a factor of 6 from 1960 to 1963 (Appendix 

Figure 7). Since then it has fluctuated around 100 million hooks. Much 

of the fishing since 1970 in the South Pacific has been by Korean longliners, for which catch-effort data were not available; consequently the 

data on fishing effort is less reliable since 1970. 
25 

Catch Rate Trends 

Catch rate of striped marlin for the entire Pacific fishery shows a 

slow long-term decline (Appendix Figure 7). From 1952 to 1975 the catch 

rate declined approximately 50%. 

Catch rate in the North and South Pacific shows long-term declines 

since the mid-1950's (Appendix Figure 7). 

sharper in the South Pacific than in the North Pacific. The catch rate 

trend in the North Pacific closely followed that in the entire Pacific. 

The decline in the South Pacific catch rate was considerable from 1954 

to 1957 following the 3 years of rising catch rates. 

South Pacific catch rate declined in a manner similar to that in both the 

entire Pacific and the North Pacific. 

The decline has been much 

After 1957, the 

STOCK STRUCTURE 

The stock structure of the Pacific striped marlin is not clear. 

While many hypotheses may be advanced, considering the distributional 

patterns and other biological data, the two most likely hypotheses are: 

1. A slngle-unit stock in the Pacific. 

The single stock hypothesis is supported by the continuous distributlon of striped marlin in a horseshoe-pattern. 

2. A two-stock structure, where the stocks are separated roughly 

at the Equator into North Pacific and South Pacific stocks with some 

intermixing in the eastern Pacific (Appendix Figure 5). 

The two-stock hypothesis is supported by morphometric differences 

between adults from the north and south regions of the western Pacific 

(Kamimura and Honma 1958) and perhaps also in the eastern Pacific (Howard 

and Ueyanagi 1965). Honma and Kamimura (1958) noted that there is a zone 

of low longline catch rates along the Equator which suggestg a separation 

of north and south stocks at the Equator. 

two centers of spawning, one in the north and one in the south, although 

gonad index data (Kume and Joseph1969a) suggest that spawning occurs 

throughout the eastern tropical Pacific, the supposed region of stock 

mixing. 

Larval distribution suggests 

POPULATION PARAMETERS 

Few studies have concentrated on quantifying critical population 

parameters of striped marlin. 

and need refinement. 

Most published estimates are preliminary 

Eldridge and Wares (1974) estimated that Pacific striped marlin reach 

sexual maturity between 140 and 165 cm and has a single mid-summer spawning period. 

for females 155 to 180 cm. Ski-llman and Yong (1974, 1976) reported 

Fecundity is in the order of 11.3 x lo6 to 28.6 x lo6 eggs 
26 

length-weight relations and an age-length relation for the Pacific striped 

marlin. The length-weight relation, sexes combined is 

W = (5.7126 x L3*3756 

where W = weight in kilograms and L = total length in centimeters. 

mates of other population parameters are given in Appendix Table 5. 

EstiIt must be noted that with the exception of the growth curves, which 

still need to be verified, the other population parameters should be considered preliminary and serve only to indicate possible orders of magnitude. 

STOCK ASSESSMENT 

Very little data on the fisheries and population dynamics of striped 

marlin including reliable estimates of population parameters and sizecomposition data, are available. Total catch figures are available, 

although in some instances the catch estimates are based on marginal sample data. 

series of catch and effort data. Because of this lack of reliable data, 

a simple approach was used in assessing the state of the Pacific striped 

marlin stocks which consisted of the determination of trends in longline 

catch rate and effort and the use of production model analysis. 

The Japanese longline fishery has provided the longest time 

The results of the production model analysis should be interpreted 

cautiously, however, as it relies on the basic assumptions that (1) the 

model is applied to a unit stock, (2) equilibrium conditions apply to 

the stock, and (3) the age-groups being fished have remained and will 

continue to remain the same. These assumptions have not been adequately 

verified for striped marlin. 

Northern Stock 

The production model estimated an MSY of about 70,000 mt produced 

by an optimum effective effort of about 13.2 million hooks per 5’ square 

for striped marlin in the North Pacific (Appendix Figure 8). This estimate of optimum effective effort is beyond the range experienced by the 

fishery (maximum of 1.5 million hooks per 5’ square) so little confidence 

should be placed on the estimate of MSY. 

however, it appears that modest increase in effort could result in increased 

yields, although the margin of return would not be proportional to the 

increase in fishing effort. 

From the trend of the data, 

Southern Stock 

The production model estimated an MSY of 6,000 mt obtained by an 

optimum effective effort of 0.6 million hooks per So square (Appendix 

Figure 8). 

for 1952-72 reasonably well. Data points for 1973-75 cluster at the 

optimum effective fishing effort but fall considerably below the equilibrium yield curve. This suggests the possibility that (1) there is 

The equilibrium yield curve passes through the data points 
27 

28- 1 I I 1 168 'I I 

PACIFIC -WIDE 

24 - - 

20- - 

16 - - 

12 - - 

- 

- 

/ 

/ 

0 I I I I I I I 

0 4 8 12 16 20 24 28 32 

04 8 12 16 0 4 8 12 16 

STRIPED MARLIN 

Appendix Figure 8.--Production models for hypothesized striped marlin 

stocks in the Pacific. 
28 

considerable variability around the equilibrium yield curve because of 

large variation in recruitment, (2) the model is inappropriate, (3) there 

has been subtle changes in the fishing operation of the Japanese longline 

fleet that are not accounted for in the estimation procedure for effective fishing effort, or (4) a change has occurred in the age structure 

of the stock in the last few years (1973-75), thus violating an assumption of the model and making the inclusion of these data with the 1952-72 

data series inappropriate. If case (1) is true, fishing effort is currently at about the optimum level and further increases in fishing effort 

would not result in substantial increases in long-term yield. If case 

(2) is true other population dynamics models must be used for stock 

appraisal. If case (3) is true, depending on the type of adjustments, 

the conclusion could range from an overfished to underfished condition. 

And if (4) is true the 1973-75 data should perhaps be treated separately, 

assuming they represent new equilibrium conditions. It therefore appears 

that further research is required to determine the reason for the deviation of the 1973-75 points to obtain an accurate appraisal of stock condition of striped marlin in the South Pacific. 

Pacific-Wide Stock 

The production model estimated an MSY of about 24,000 mt produced by 

an optimum effective effort of 3.4 million hooks per 5" square (Appendix 

Figure 8). Catches for 1964-75 ranged from about 14,500 to 27,100 mt, 

produced by an average effective effort ranging from about 1.5 to 2.25 

million hooks per 5" square. From production model results it appears 

that the stock is not being overexploited and further increases in fishing 

effort could result in increased yield on the long term. However, the 

1973 to 1975 data points are considerably lower than the equilibrium line 

and the cautions expressed above for the South Pacific stock apply here. 

OVERALL STOCK APPRAISAL 

From the Pacific-wide perspective, the striped marlin stock appears 

to be in good condition and may be capable of providing increased yields 

with modest increases in fishing effort. 

increased yields from the North Pacific fishery than the South Pacific 

fishery, which may be operating at or beyond the MSY level. 

The outlook is better for 

RE COMMENDATIONS 

Statistics 

The statistics on catch, effort, and catch rate of striped marlin 

need improving. Catch and effort data, particularly for the Korean 

longline fleet after 1970, are needed. In addition, representative 

length-composition data by sex are needed for development of a more 

accurate assessment of the state of the stocks. 
29 

Research 

Better information on the stock structure of the population is 

needed. Simulation studies should be undertaken to evaluate the sensitivity of stock assessments to various stock structure hypotheses before 

a major program for stock identification is undertaken. Such studies 

would not only provide information on whether a stock identification 

program is necessary but also provide information on the design of an 

effective program. 

Better estimates of population parameters are needed for refined 

assessment techniques, such as yield-per-recruit and cohort analyses. 

First priorityshould be given to verification of age-growth equations. 

Better estimates of effective fishing effort from the longline fisheries 

are also needed, especially If there have been subtle changes in the 

operations which are not accounted for in the estimation technique. 

Management 

The striped marlin stocks appear to be in good condition and not. 

in need of active management at this time. The fishery, however, should 

be monitored closely considering the uncertainty in the stock appraisals, 

especially in the South Paciflc where only a modest increase in yield 

might be available. 
30 

SAILFISH, ISTIOPHORUS PLATYPTERUS, AND SHORTBILL SPEARFISH, 

TETRAE'TURUS ANGUS TIROS TRI S 

James L. Squire and Ziro Suzuki, Rapporteurs 

REVIEW OF FISHERIES DATA 

Sailfish, Istiophorus platypterus, are widely distributed in the 

Pacific but they are generally regarded as a species common to waters 

near continental or island areas. Their latitudinal limits in the Pacific 

appear to extend from 40"-45"N to about lat. 40"s (Appendix Figure 9). 

Shortbill spearfish, Tetrapturus angustirostris, are widely distributed in tropical and temperate offshore waters of the central Pacific and 

their distributional limits are similar to that of sailfish (Appendix 

Figure 9). However, relatively small numbers of this species are taken 

on tuna longlines. Because the two species are often combined in the 

longline catch statistics, the distributional chart, which is based on 

longline catches, should be considered tentative. 

The major fishery for sailfish and shortbill spearfish is the commercial longline fishery conducted principally by Japan, Taiwan, and 

Republic of Korea, which accounts for about 90% of the Pacific catch of 

these species, Important areas of sailfish catches on longlines are in 

the eastern Pacific to approximately 600 miles offshore from North 

America and in the western Pacific from off northeast Australia and Papua 

New Guinea, and from the Philippine Islands to the southern islands of 

Japan. In the western Pacific, this species has been taken for several 

decades incidentally to tunas on longlines; in the eastern Pacific, 

substantial fishing effort was not applied until about 1965. 

of sailfish are also made by harpoons and gill nets, and there is a 

recreational fishery in the eastern Pacific, off central Mexico to 

Ecuador. 

Coral Sea around Papua New Guinea and in the East China Sea. 

Catches 

In the western Pacific, sailfish are taken primarily in the 

One of the shortcomings of the sailfish and shortbill spearfish data 

is that catches of both species are combined in the catch statistics, and 

determining the exact catch of each species is difficult. Also, catch 

data by species are not available for the Republic of Korea and Taiwan 

fisheries. An additional problem is that some other incidentally caught 

species may be reported by fishing vessels in the sailfish/spearfish group. 

Catch Trends 

Before 1964 the annual Pacific landings of sailfish and shortbill 

spearfish amounted to less than 8,000 mt (Appendix Table 3; Appendix 

Figure 10). A marked increase in catch to 12,800 mt was recorded in 

1965. 

around the 12,000 mt level and thereafter declined to about 5,500 mt in 

1975. 

During the remainder of the 1960's, the catches continued at 

The actual catches of sailfish and shortbill spearfish are probably 
31 

L 
32 

lower than reported because totals include catches of species other than 

sailfish or shortbill spearfish. 

Effort Trends 

Sailfish.--Effective fishing effort in the Japanese longline fishery 

for sailfish was summarized for two areas: the western (Area 1) and 

eastern Pacific (Area 2) (Appendix Figure 11). Effective effort for 

sailfish in the western Pacific showed large fluctuations and no obvious 

trends. 

was before and after that period. In the eastern Pacific, the effective 

effort did not increase substantially until 1965, then it peaked in 1968, 

and declined gradually through 1975. 

Effective effort was higher during the 1961-67 period than it 

Appendix Table 3.--Annual combined landings of Pacific 

sailfish and shortbill spearfish, 1952-75 by number of 

fish and metric tons. 

Year Number of fish (lo3) Metric tons (lo3) 

1952 

1953 

1954 

1955 

1956 

1957 

1958 

1959 

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

1975 

72.6 

119.2 

88.2 

120.6 

115.5 

171.6 

122.0 

142.0 

129.2 

152.2 

216.3 

289.3 

250.4 

598.1 

435.3 

487.3 

676.5 

333.2 

466.4 

260.3 

230.0 

304.3 

253.5 

191.3 

2.0 

3.3 

2.4 

3.3 

3.2 

2.8 

3.4 

3.4 

5.0 

4.8 

6.8 

7.9 

6.1 

12.8 

11.1 

11.8 

12.5 

12.8 

9.0 

8.1 

8.6 

8.7 

7.1 

5.5 
33 

. 

14 

12 

la 

8 

6 

4 

2 

C 

SAILFISH a 

SHORTBILL 

IIIllllllllllllllll11111 

1955 I960 1965 I970 197! 

YEAR 

Appendix Figure 10.--Catches of sailfish and shortbill spearfish 

in the Pacific, 1952-75. 

Longline fishing in the Pacific is also conducted by vessels of the 

Republic of Korea and Taiwan. This effort is principally in the south 

central and southwestern Pacific. The Taiwan nominal effort, which is 

centered in the southwestern and north central Pacific, appears to have 

paaked in 1973 to 54.7 million hooks and declined to 39.3 million hooks 

in 1976. The amount of effort expended by the harpoon, gill net, and 

recreational fisheries is unknown. 

Shortbill spearfish. Longline effort data for shortbill spearfish 

north and south of the Equator (Appendix Figure 12) were available in 

terms of nominal effort (Appendix Figure 13). In the northern area nominal fishing effort increased from 1952 through 1961 and fluctuated between 

about 180 million and 230 million hooks from 1962 to 1975. In the southern area, effort increased from 1952 through 1963, declined from 1964 

through 1968, and has been stable since 1969. 
34 

I I AREA2 

3t 

-e I1 I I I I I I I I lo 

I955 1960 1965 1970 1975 " 

YEAR 

Appendix Figure 11.--Catch rates and effective fishing effort 

for sailfish in the Pacific, 1952-75. 

Catch Rate Trends 

Sailfish.--The sailfish catch rate in the western Pacific (Area 1) 

fluctuated between about 6 and 14 fish per 10,000 hooks from 1952 to 

1959 and has been declining since 1959 (Appendix Figure 11). The average 

catch rate from 1960 to 1975 was about one-half of that during 1952-59. 

The sharp decline in 1975 may be partially the result of deep fishing 

for bigeye tuna, Thunnus - obesus, :I method which is less effective for 

sailfish, which tend to inhabit the upper layers of the ocean. 

In the eastern Pacific (Area 2) there were large fluctuations in a 

generally rising trend of catch rates from 1959 to 1965; subsequently 

the catch rate has fluctuated less on a downward trend (Appendix Figure 

11). 

during the high catch rate period of 1964 to 1968. 

The 1975 catch rate is approximately two-thirds of that observed 
35 

A 
36 

n 

YEAR 

Appendix Figure 13.--Catch rates and nominal fishing effort for 

shortbill spearfish in the Pacific, 1952-75. 

Shortbill spearfish.--Because shortbill spearfish and sailfish 

catches are pooled in the catch statistics, shortbill spearfish catches 

were estimated by using historical sailfish to shortbill spearfish catch 

ratio data; the catch rate is based on nominal effort (Appendix Figure 

11). The catch rate for shortbill spearfish in the northern area 

increased from a level of four fish per 100,000 hooks during the period 

1952 through 1961, to an average of about eight fish per 100,000 hooks 

in recent years. The southern area annual catch rate shows a smaller 

increase, from about 20 fish per 100,000 hooks during the period 1952 

through 1962, to about 30 fish per 100,000 hooks since 1962, a much 

better (by a factor of 4) catch rate than in the northern area. 

STOCK STRUCTURE 

Sailfish.--Based on the distribution of larvae and longline catch 

rates, a possible two unit, western and eastern Pacific, stock structure 

for sailfish was suggested (Appendix Figure 9). 
x 

37 

Shortbill spearfish.--& similar types of evidence, a two unit, 

northern and southern, stock structure for shortbill spearfish was proposed (Appendix Figure 12). 

POPULATTON PARAMETERS 

Sailfish.--Kume and Joseph (1969b) determined the following lengthweight relation for eastern Pacific sailfish. 

loglo Y = -3.9357 + 2.4156 loglo X, 

and Wares and Sakagawa (1974) the following: 

loglo Y = -4.360 + 2.628 loglo X, 

where Y is weight in kilograms and X is eye-fork length in centimeters. 

, Skillman and Yong (1974) determined the length-weight relation for 

central Pacific sailfish as follows: 

W = 2.0739 x L2-6054, 

where W is weight in kilograms and L is snout-fork length in centimeters. 

Other population parameters for sailfish are found in Appendix 

Table 5. 

Shortbill spearfish.--Kume and Joseph (1969b)determined the following length-weight relation for eastern Pacific shortbill spearfish: 

loglo Y = -6.8146 + 3.7242 loglo X, 

where Y is weight in kilograms and X is eye-fork length in centimeters. 

Skillman and Yong (1974) determined the following length-weight 

relation for central Pacific sailfish: 

W = 5.0083 x L3.8338, 

where W is weight in kilograms and L is snout-fork length in centimeters. 

No other population parameters for shortbill spearfish are available. 

STOCK ASSESSMENT 

Because of problems with the basic longline data relative to species 

separation of sailfish and shortbill spearfish catches and unknown amounts 

of other species included in the sailfish/spearfish catch data, production 

model analysis was not performed. Appraisal of stock condition was therefore based on estimates of apparent abundance as deduced from Japanese 

longline data. 
38 

Sailfish.--The substantial decline in catch rate that occurred 

between 1953 and 1975 in Area 1 suggests that any increase in effort probably will not result in a substantial increase in catch and if further 

increases in deep longlining occurs, the catch would decrease even if 

effort remains constant. 

Since 1965 there has been a decrease in catch rate in Area 2, although 

the decline was not as sharp as that in Area 1. 

an increase in effort may result in a slight increase in catch. However, 

if effort is switched to deep longlining, the catch could decline without 

a change tn noqinal effort. 

Thus, it is possible that 

Shortbill spearfish.-The catch rate in both the northern and southern 

areas has generally increased from 1952 to the present. Therefore, fishing 

has not resulted in a decline in stock abundance and any increase in effort 

should result in an increase in catch. 

OVERALL STOCK APPRAISAL 

Catch rates of sailfish in both the western and eastern Pacific 

declined substantially, and any increase in effort will probably produce 

little increase in catch. 

The catch for shortbill spearfish has shown a general increase, and 

any increased effort should result in higher catches. 

RECOMMENDATIONS 

Stat is t ics 

The workshop recommended that the maintenance of accurate statistics 

on the catch of sailfish and shortbill spearfish be encouraged and that 

better estimates be made of the catch of the gill net and recreational 

fisheries. 

Research 

The workshop recommended that investigations be conducted on the 

length/weight/sex by quarters of the two species to Provide coverage of 

the suggested stocks and that studies on age and growth be conducted 

throughout the range of the species. 

The need to determine estimates of interchange rates among the suggested and assumed stocks and the need to define spawning areas and seasons 

for both specAes, with particular emphasis on the south and eastern Pacific, 

were indfcated. 

It was also recommended that currently available data be analyzed with 

production model analysis, using different combinations of catch statistics 

to evaluate biases in catch estimates and the d€fferent stock structure 

hypotheses. These outputs should then he evaluated to determine what additional studies might be needed. 
39 

Management 

'.. 

A general management recommendation cannot be made at this time. From 

current analyses of the data, there appears to be no critLca1 management 

problems with the stocks at this time. 

there has been a substantial decline in catch rate for sailfish. It is 

recommended that the fisheries be monitored at an increased level and that 

the evaluation of data be intensified, 

However, it is recognized that 

c 
40 

SWORDFISH, XIPHIAS GLADIUS 

Gary T. Sakagawa and Robert R. Bell, Rapporteurs 

REVIEW OF FISHERIES DATA 

Swordfish, Xiphias gladius, occur in waters off California to Chile 

in the eastern Pacific, throughout the central Pacific, and in waters from 

Japan to Australia in the western Pacific (Appendix Figure 14). They are 

caught by surface gears (harpoons, gill nets, and handlines) and by longlines. Nations participating in the fishery include: United States 

(harpoon fishery off California) ; Chile, Mexico, and Peru (coastal handline 

fisheries); Japan (Pacific-wide longline fishery and a coasta1,mainly driftgill net fishery off Honshu and Hokkaido); Taiwan (Pacific-wide longline 

fishery and a coastal, primarily longline and harpoon fishery); and Republic of Korea (Pacific-wide longline fishery). Swordfish are not caught in 

significant quantities by recreational fishermen anywhere in the Pacific. 

The surface fisheries are directed to catching swordfish whereas the 

longline fisheries are generally directed to catching tunas. In certain 

regions of the northwestern Pacific, however, longlines are set at night 

specifically for swordfish. 

mid-1960’s and most of the sets are now daylight operations directed at 

tuna with incidental catches of swordfish. 

This practice has been on a decline since the 

Catch Trends 

The total annual Pacific catch of swordfish increased from 11,300 mt 

in 1952 to a record high of 24,300 mt in 1961. 

fluctuated within a narrow range of 10,100 to 18,900 mt, averaging 13,800 

mt annually (Appendix Table 4; Appendix Figure 15). Most of the catch is 

landed by the Japanese longline fleet (about 58% in 1975) in the northwestern Pacific (about 75% in 1975). 

Since then the catch has 

Effort Trends 

Effective fishing effort for Pacific swordfish has fluctuated between 

270 million and 550 million hooks (Appendix Figure 16). The level in 1975 

was about 300 million hooks. 

Catch Rate Trends 

The longest available time series of catch rates is for the Japanese 

longline fleet. Total Pacific catch rates for this fleet reached a peak 

of about 10 fish per 10,000 hooks in 1958, dcclined to a low of 4 fish 

per 10,000 hooks in 1967, and since then stqbilized at about 5 fish per 

10,000 hooks (Appendix Figure 16). 
41 
42 

Appendix Table 4,--Swordfish catches (metric tons) by countries 

for the Pacific Ocean, 1952-75. 

Republic United 

Year Japan Taiwan of Korea States Chile Peru Others Total 

1952 

1953 

1954 

1955 

1956 

1957 

1958 

1959 

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

197 5 

11,182 

11,604 

13,301 

16,220 

12,167 

15,771 

20,815 

19,136 

22,944 

23 , 636 

14,037 

13,775 

9,703 

11,955 

13,283 

13,083 

12,983 

15,612 

11,301 

9,182 

8, $46 

9,644 

9,517 

11,274 

77 

185 

254 

250 

247 

262 

273 

432 

544 

300 

300 

300 

600 

838 

974 

1,023 

1,053 

1,149 

1,111 

1,269 

1,157 

1,099 

41 

47 

55 

89 

115 

115 

11 5 

115 

115 

11 5 

157 

85 

14 

80 

16 3 

222 

279 

265 

19 2 

218 

23 

58 

109 

194 200 

277 200 

181 200 

118 200 

610 300 

558 200 

91 200 

157 100 

363 400 

384 218 

512 218 

300 

200 

1,300 

800 

1 , 200 

2 , 400 

200 

600 

1,900 

270 

158 

11,339 

11,689 

13 ,.392 

16,485 

12,584 

16,243 

21,341 

19,663 

23,409 

24,286 

14,604 

14 , 133 

10,112 

12,949 

14,601 

100 15,230 

100 18,934 

100 15,727 

100 11,037 

100 11,029 

100 13,791 

3 11,664 

13,376 

' 15,649 

STOCK STRUCTURE 

The stock structure of the swordfish population of the Pacific Ocean 

is not clearly known. 

longline catch rates suggest that the population consists of either (1) a 

single, Pacific-wide stock, or (2) three separate stocks with centers of 

concentration in the northwestern (Area l), southwestern (Area 2), and 

eastern (Area 3) regions of the Pacific Ocean (Appendix Figure 14). 

Available data on distribution of larvae and on 

POPULATION PARAMETERS 

Estimates of basic, critical, population parameters for swordfish are 

The 

lacking. Available estimates are shown in Appendix Table 5. 

estimates of growth and mortality rates that are judged to be crude. 

difficulty in obtaining reliable estimates appear to be limited by the 

ability to age swordfish. A reliable aging technique has not yet been 

developed and most population parameters rely on age-dependent data. 

They include 
43 

c 

30 

25 

20 

15 

10 

5 

0 

SWORDFISH - 

111111111111111111111111 

1955 1960 1965 I970 1975 

YEAR 

Appendix Figure 15.--Total catch of swordfish in the Pacific, 

1952-75. 

STOCK ASSESSMENT 

.- 

e 

The condition of the swordfish stocks of the Pacific was evaluated 

based on different hypotheses about the stock structure of the population: 

hypothesis 1, a single Pacific-wide stock, and hypothesis 2, three separate 

stocks. Because of limited data on the stocks the evaluation was restricted 

prllmarllly to the use of production model analysis. 

Single Pacific-Wide Stock 

The relation of catch and effective fishing effort, assuming a single 

Pacific-wide stock is shown in Appendix Figure 17. 

into two clusters separated by a break between 1963 and 1964, which corresponds approxbately to the period when the operational methods in the longline fishery changed in the productive northwestern fishing area. 

indicated earlier, longline night fishing which is directed at swordfish, 

was the predominant manner of fishing in the northwestern region prior to 

the mid-1960's. Since then, fishing in that region has become more a day 

operation for tunas raLher than a night operation for swordfish. 

The data points fall 

As 
44 

-- 

- 

12 

IO 

8 

6 

4 

2 

0 

500 

-400 

300 

200 

IIIIIIII I111111111111111 6oo 

,EFFECTIVE EFFORT 

?\ SWORDFISH ,! 

?* a I\ 

I5 t\ I\ 

i b\ 

\ I I 

\ 

\ d 

/ 

I \ 

lllilllllllllllllllllliilo 

I955 1960 1965 1970 1975 

YEAR 

Appendix Figure 16.--Pacific-wide catch rate and effective 

fishing effort for swordfish, 1952-75. 

Production model analysis of the separate clusters of points gave no 

solution for the 1964-75 data series, and an MSY estimate of 20,000 mt per 

year with 2.2 million hooks per 5" square for the 1952-63 data series. 

Presumably during the 1952-63 period the fishery was more efficient in 

catching swordfish than during the 1964-75 period. The current (average 

for 1966-75) catches of about 14,100 mt produced by 1.8 million hooks per 

5' square indicate that the fishery does not appear to be overexploiting 

the stock and that the stock is in good condition. 

Three Separate Stocks 

Complete data for production model analysis, assuming three stocks 

;In the Pacific were not available for examination. 

condition of the stocks was therefore based on estimates of apparent 

abundance from Japanese longline data for 1952-75. 

An appraisal of the 
45 

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00 

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

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

+A II 12 13 14 15 16 17 18 19 20 21 22 

to5 HOOKS/ 50 SQUARE 

Appendix Figure 17.--Relationship of catch of swordfish and effective 

fishing effort. 

is shown for data for 1952-63 only. 

The equilibrium yield curve (Schaefer production model) 
47 

In the northern region (Area I), the longline catches ranged from 

about 6,800 to 22,900 mt (Appendix Figure 18); the catch rates showed a 

gradual decline from about 20 fish per 10,000 hooks in 1958 to 8 fish per 

10,000 hooks in 1971 (Appendix Figure 19). Since 1971 the catch rate gradually recovered to the current level of 12 fish per 10,000 hooks in 1975. 

In the southwestern region (Area 2) the longline catches showed a 

gradually increasing trend (Appendix Figure 18); the catch rates fluctuated 

between two fish per 10,000 hooks and three fish per 10,000 hooks during 

the period 1952-67 (Appendix Figure 19). The rate then increased to the 

current high level of four fish per 10,000 hooks. 

Longline catches in the eastern Pacific (Area 3) showed an increasing 

trend after 1960, following a period of small catches from 1952 to 1960 

(Appendix Figure 18); the catch rates gradually increased from about two 

fish per 10,000 hooks in 1954 to six fish per 10,000 hooks in 1968 (Appendix Figure 19). In 1969 and 1970 the catch rates increased sharply to a 

record high of about 11 fish per 10,000 hooks before declining to a level 

of about 5 fish per 10,000 hooks in 1971-75. 

OVERALL STOCK APPRATSAL 

The swordfish stocks of the Pacific Ocean appear to be healthy and 

capable of sustaining increased yields with increased effort. However, 

should the longline fishery resort to night fishing, which was the standard 

method of fishing in some areas prior to the mid-l960's, then the greater 

efficfency of the gear could result in the catch exceeding the MSY with 

about a 25% increase in the current levels of fishing effort. 

RECOMMENDATIONS 

Statistics 

Longlining for swordfish is most effective during the night, whereas, 

longlining for tunas is most effective during the day. 

1960's, longlining in the more productive swordfish areas, especially in 

the northwestern Pacific, was conducted during the night. Since then this 

practice has decreased as the fishery has been targeting the higher priced 

tunas, 

Prior to the midThis change in fishing practice has complicated the longline statistics 

which are used to measure apparent abundance of swordfish. 

tistics currently do not identify type of fishing, i.e., night and day 

operations, and more precise stock assessments based on the longline data 

will require separation of the data. The participants, therefore, recommended that the longline catch-effort statistics be separated into type 

(day and night) of operations. 

Published staThe participants also recommended that size and sex data be collected 

from all fisheries, and catch-and-effort data be collected from the surface 

fishertes. These data are essential for using more sophisticated assessment techniques and for obtaining more precise management advice. 
48 

25 

20 

15 

IO 

5 

0 

1 

0 

PACIFIC -WIDE 

YEAR 

Appendix Figure 18.--Swordfish catch in the Pacific Ocean, 

1952-75. 
49 

28 

24 

20 

16 

12 

8 

4 

0 

- 240 

-- 200 

- 160 

- 120 

- 80 

I 

YEAR 

Appendix Figure 19.--Catch rates and effective fishing effort for 

swordfish in the Pacific, 1952-75. 
50 

Research 

Information on stock structure of a fish population is important for 

proper management of the resource. For Pacific swordfish, the stock structure is not clearly known although available data suggest that the population might consist of a single Pacific-wide stock or possibly, three 

separate stocks. Available techniques for stock identification are 

expensive to apply and not entirely reliable in producing clear results. 

The participants therefore recommended that different stock structure 

hypotheses be tested using existing fisheries data to determine their 

impact on assessments before any major program for stock identification of 

swordfish is considered. 

The key to more precise stock assessments for swordfish is more 

reliable information on stock densities and better estimates of population 

dynamics parameters. 

swordfish receive more research attention since this is important for estimating population dynamics parameters. 

The participants recommended that methods of aging 

Management 

With current levels of fishing effort (about 1.8 million hooks per 5" 

square) and the current mode of longline operations (fishing predominantly 

during the day), the swordfish stocks are not being exploited beyond the 

estimated MSY of about 20,000 mt for the Pacific-wide stock. However, the 

fishery should be monitored closely for changes in the mode of operation, 

especially changes to night fishing, which could result in the stocks being 

exploited beyond MSY. 
Y 

51 

BLACK MARLIN, MAKAIRA INDICA 

Jerry A. Wetherall and Rong-Tszong Yang, Rapporteurs 

... Black marlin, Makaira indica, occur across the entire Pacific Ocean 

between about lat. 45ON and 50's. Their latitudinal distribution is somewhat more restricted in the eastern than in the western Pacific (Appendix 

Figure 20). Catch rates in the tuna longline fisheries show that the density of black marlin is generally very low except in certain coastal 

waters. In the western Pacific, seasonal concentrations of this species 

are seen in such areas as the East China Sea and the Coral Sea. The Coral 

Sea is assumed to include spawning areas for black marlin as evidenced by 

gonad condition and larval occurrence. In the eastern Pacific, high densities are observed in the coastal waters of Panana and Ecuador. In the 

mid-Pacific region, occurrence of black marlin is highest in the vicinity 

of islands. c 

Catch Trends 

4 

REVIEW OF FISHERIES DATA 

The total catch of black marlin in the Pacific rose to a peak of 

about 6,500 mt in 1956, then dipped to about 3,100 mt in 1959 and fluctuated between about 2,000 and 4,000 ntt from 1960 to 1975 (Appendix Table 6; 

Appendix Figure 21). 

marlin catches in the Pacific; it is believed that some catches are 

unreported . 

There are uncertainties in the estimates of black 

Most of the black marlin catches in the northwestern Pacific are made 

by Taiwan commercial fishermen using mostly tuna longlines on short-range 

vessels under 50 GT, or using harpoons. 

longliners in the area are relatively minor. 

Catches made by Japanese tuna 

In the southwestern Pacific, most of the black marlin catches are 

made by Japanese tuna longliners and lesser amounts are taken by Taiwan 

and Republic of Korea vessels. 

ery for black marlin primarily off Cairns, Australia. 

There is also an active recreational fishA recreational fishery accounts for some of the catch of black marlin 

in the eastern Pacific but almost all the catch in this area is made by 

Japanese longliners. 

Effort Trends 

Effort data have been summarized for four areas in the Pacific, 

northwestern (Area l), southwestern (Area 2), eastern (Area 31, and 

western (Area 4) (Appendix Figure 22),where black marlin are relatively 

densely distributed. Black marlin occupying these areas may represent 

separate stocks. Because total catch figures are used to estimate effective fishing effort, these estimatesare biased to the same extent as the 

corresponding catch estimates. 
52 
53 

Appendix Table 6.--Black marlin catches (metric tons) 

by countries in the Pacific Ocean, 1952-75. 

Republic 

Year Japan Taiwan of Korea Total 

1952 

1953 

1954 

1955 

1956 

1957 

1958 

1959 

1960 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

197 2 

1973 

1974 

1975 

1,806 

3,188 

4,713 

3,690 

5 , 107 

2 , 581 

1,905 

1,938 

2 , 312 

2 , 852 

2,580 

2,205 

3,439 

3,225 

2 , 034 

1 , 588 

2,053 

1,644 

1,773 

1,424 

1,614 

1,175 

96 2 

4 , 443 

657 

1 , 689 

2,023 

1,269 

1,967 

1,176 

783 

858 

1,214 

600 

600 

600 

400 

648 

661 

343 

453 

7 91 

1 , 890 

1,996 

1,763 

1 , 724 

104 

154 

113 

150 

110 

110 

110 

110 

110 

110 

- ~~ 

1,806 

3,188 

5,370 

5,379 

6,466 

6,376 

4,548 

3,081 

2,721 

3,170 

4,066 

3 , 180 

2,805 

4,039 

3,729 

2,836 

2,362 

2,546 

2,207 

2,674 

3,424 

3,720 

3 , 048 

2,796 

Effective fishing effort from 1952 to 1975 has been erratic and does 

not show any discernible trends in Areas 1, 2, and 4, 

Pacific (Area 3), where the Japanese tuna fishery commenced in 1956, the 

effective fishing effort has been on a generally increasing trend. 

In the eastern 

Catch Rate Trends 

In the northwestern Pacific (Area l), the catch rate reached a peak 

in 1953 and declined to its lowest level in 1975. In the southwestern 

Pacific (Area 2), the catch rate reached a peak early in the development 

of the fibhery in 1955, declined to less than four fish per 10,000 hooks 

in 1957 and fluctuated between about one and three fish per 10,000 hooks 

from 1958 through 1975. The catch rate in the eastern Pacific (Area 3) 

reached a peak in 1957 and declined thereafter. 

(Area 4) catch rate reflects the same trends as that in the constituent 

areas (Areas 1 and 2). 

The western Pacific 
54 

,Ill’lllilll’llllllI1lllll I955 1960 1965 I970 I 975 

YEAR 

Appendix Figure 21.--Total catch of black marlin in the Pacific, 

1952-75. 

STOCK STRUCTURE 

The stock structure of black marlin in the Pacific is not clear; 

however, their restricted coastal distribution and the presence of isolated 

high catch-rate areas suggest the possible existence of more than one stock 

in the Pacific. It has been suggested that there may be two or three 

stocks; one in the eastern Pacific and one or two in the western Pacific 

(Appendix Figure 20). 

ity of mixing between black marlin in the Indian Ocean and the western 

Pacif ic. 

The situation is complicated by the strong possibil

POPULATION PARAMETERS 

Owing to a lack of black marlin age data, no estimates of mortality 

have been made. 

for black marlin are found in Appendix Table 5. 

Estimates of K and L, (von Bertalanffy growth parameters) 
5 5 

c 

100 

80 

60 

40 

20 

0 

IO I I I'I 

8- AREA 3 

I I I I I I I I I, I 

6- -60 

2- 20 

4- - 40 

- 

0 

YEAR 

Appendix Figure 22.--Catch rates and effective fishing effort 

for black nlarlin in the Pacific, 1952-75. 

STOCK ASSESSMENT 

Because of the uncertainty in total catch figures and stock structure, 

no attempt was made to fit production models or to estimate MSY for black 

marlin in any area in the Pacific. 

estimated catch and effort were examined (Appendix Figure 23). The consensus of the participants was that a reliable production model analysis 

will require a better accounting of catches. 

However, the relationships between 
56 

1 1 1 I I I 56 28 

- 

-5 20 - 

16 - 

67 - 

68 

- 

1 

I I I I I 

34 567 

20- 

16 

12 

8- 

4- 

2 :I I 

61 - 

- 

72 

53 

AREA 2 

52 

6 J ;- 1 I/ AREA3 I 

I I I I J 

6 8 IO 12 14 

24 I I I I I I1 

01 I I I I I I1 

0 4 8 12 16 20 24 

80 I I I I I I 

55 754 

100,000 HOOKS / 5O SQUARE 

Appendix Figure 23.--Relation between catch and effective effort 

for black marlin in four areas in the Pacific. 

OVERALL STOCK APPRAISAL 

While no definitive assessments of black marlin stocks are yet available, the substantial decline in catch rates from the early 1950's to 1975 

suggests that a very large increase in total catch over recent levels is 

probably not sustainable. 

RECOMMENDATIONS 

Statistics 

For improved stock assessments of black marlin, it is essential that 

complete catch and nominal effort statistics be made available from all 

harvesting nations, especially the Repuhlic of Korea, Japan, and Taiwan. 
57 

In addition, statistics on total catch and effort should be gathered 

systematically from recreational fisheries, particularly off northwest 

Australia. 

Thorough stock assessments will require extensive data on the size 

composition of black marlin catches in commercial and recreational fisheries. These statistics should be acquired over all time-area strata. 

Research 

.. 

Continued research is required to evaluate the status of black marlin 

stocks. 

ture, to better estimate total catches, and to validate the stock density 

measures. 

Attention must be paid to improve understanding of stock strucIn view of the importance of population structure to proper stock 

assessment, the tagging programs currently underway should be maintained. 

Finally, concerted efforts are needed to determine the age of black 

marlin and to establish age-size relationships. 

Management 

Because no MSY estimates are available, it is presently not useful 

to make any management recommendations with respect to catch or effort 

limitations. However, future analyses may show that catches of black 

marlin presently exceed MSY in some stocks, and that restraints should be 

considered. 

improved understanding of stock structure and stock dynamics. 

In any case, effective management will depend on a much 
58 

APPENDIX B 

LIST OF 

Dr. Norman W. Bartoo 

Southwest Fisheries Center 

National Marine Fisheries Service 

P. 0. Box 271 

La Jolla, California 92038 

Dr. Grant L. Beardsley 

Southeast Fisheries Center 

National Marine Fisheries Service 

75 Virginia Beach Drive 

Miami, Florida 33149 

Mr. Robert R. Bell’ 

California Dept. of Fish and Game 

350 Golden Shore 

Long Beach, California 90802 

Mr. Ramon J. Conser 

Southeast Fisheries Center 

National Marine Fisheries Service 

75 Virginia Beach Drive 

Miami, Florida 33149 

Dr. Jackson Davisz 

South Atlantic Fishery Management 

1 Southpark Circle 

Charleston, South Carolina 19407 

Counci 1 

Dr. Peter M. Miyake 

International Commission for the 

Conservation of Atlantic Tunas 

General Mola 

17 Madrid-1, Spain 

Dr. Gary T. Sakagawa 

Southwest Fisheries Center 

National Marine Fisheries Service 

P. 0. Box 271 

La Jolla, California 92038 

Mr. Richard S. Shomural 

Southwest Fisheries Center 

National Marine Fisheries Service 

P. 0. Box 3830 

Honolulu, Hawaii 96812 

1pacifi.c section only. 

2Atlantic section only. 

PARTICIPANTS 

Mr. James L. Squire 

Southwest Fisheries Center 

National Marine Fisheries Service 

P. 0. Box 271 

La Jolla, California 92038 

Mr. Ziro Suzuki 

Far Seas Fisheries Research Laboratory 

1000 Orido, Shimizu 424 

Shizuoka, Japan 

Dr. Shoji Ueyanagi 

Far Seas Fisheries Research Laboratory 

1000 Orido, Shimizu 424 

Shizuoka , Japan 

Mr. Wilvan G. Van Campen’ 

Western Pacific Regional Fishery 

Management Council 

1164 Bishop Street - Room 1608 

Honolulu, Hawaii 96813 

Dr. Jerry A. Wetherall’ 

Southwest Fisheries Center 

National Marine Fisheries Service 

P. 0. Box 3830 

Honolulu, Hawaii 96812 

Dr. Rong-Tszong Yang 

National Taiwan University 

Institute of Oceanography 

Taipei, Taiwan 

wss Marian Y. Y, Yongl 

Southwest Fisheries Center 

National Marine Fisheries Service 

P. 0. Box 3830 

Honolulu, Hawaii 96812 

Mr. Heeny S. H. Yuen’ 

Southwest Fisheries Center 

National Marine Fisheries Service 

P. 0. Box 3830 

Honolulu, Hawaii 96812 

Mr. James R. Zuboy 

Southeast Fisheries Center 

National Marine Fisheries Service 

75 Virginia Beach Drive 

Miami, Florida 33149