AN ASSESSMENT OF THE SKIPJACK AND BAITFISH RESOURCES OF THE KINGDOM OF TONGA
Skipjack Survey and Assessment Programme Final Country Report No. 11
South Pacific Commission Noumea, New Caledonia September 1983
LIBRARY -2 DEC. 1983
AN ASSESSMENT OF THE SKIPJACK AND BAITFISH RESOURCES OF THE KINGDOM OF TONGA
Skipjack Survey and Assessment Programme Final Country Report No.11
South Pacific Commission, Noumea, New Caledonia September 1983 iii
PREFACE
The Skipjack Survey and Assessment Programme was an externally funded part of the work programme of the South Pacific Commission. Governments which provided funding for the Programme were Australia, France, Japan, New Zealand, United Kingdom and the United States of America, and the generosity of these governments is gratefully acknowledged.
The Skipjack Programme has been succeeded by the Tuna and Billfish Assessment Programme which is receiving funding from Australia, France, New Zealand and the-United States of America. The Tuna Programme is designed to improve understanding of the status of the stocks of commercially important tuna and billfish species in the region. Publication of final results from the Skipjack Programme, including results from the Programme's investigation of yellowfin tuna resources of the region, is continuing under the Tuna Programme. Reports for each of the countries and territories for which the South Pacific Commission works have been prepared in a final country report series. Most of these reports have been co-operative efforts involving all members of the Tuna Programme staff in some way.
The staff of the Programme at the time of preparation of this report comprised the Programme Co-ordinator, R.E. Kearney, Research Scientists, A.W. Argue, C.P. Ellway, R.S. Farman, R.D. Gillett, P. Kleiber, J.R. Sibert, W.A. Smith and M.J. Williams; Research Assistants, Susan Van Lopik and Veronica van Kouwen; and Programme Secretary, Carol Moulin.
The Skipjack Programme is indebted to many people in Tonga who helped make the fieldwork both productive and enjoyable. Officials of the Fisheries Division of Tonga are thanked for their support of the field survey and for their generous response to numerous requests for data.
Tuna Programme South Pacific Commission
For bibliographic purposes this document should be cited as follows:
Tuna Programme (1983). An assessment of the skipjack and baitfish resources of the Kingdom of Tonga. Skipjack Survey and Assessment Programme Final Country Report No.11, South Pacific Commission, Noumea, New Caledonia. V
CONTENTS
Page
PREFACE iii
LIST OF TABLES vii
LIST OF FIGURES viii
1.0 INTRODUCTION 1 1.1 Description of the Fishery 1 1.2 Previous Surveys 2 2 2.0 METHODS 2.1 Vessel and Crew 2 2.2 Research Plan 4 2.3 Skipjack Fishing and Tagging ^ 2.4 Biological Sampling ^ 2.5 Baitfishing ^ 2.6 Data Compilation and Processing ^ 2.7 Data Analysis 5
3.0 SUMMARY OF FIELD ACTIVITIES
4.0 RESULTS AND DISCUSSION " 4.1 Baitfish 6 4.1.1 Quantity of bait 6 4.1.2 Baitfish effectiveness 11 1 O 4.1.3 Consistency of baitfish supply iJ 4.1.4 Ha'apai and Tongatapu "^ 4.1.5 Baitfish culture ^ 4.2 Fishing Success/Skipjack Abundance i^ 4.3 Biological Observations on Skipjack r;? 4.3.1 Stomach contents j-k 4.3.2 Skipjack size frequency *18° 4.3.3 Sexual maturity and juvenile recruitment 22 4.3.4 Growth 24 4.4 Population Structure
4.4.1 Blood genetics and tagging o2^6 4.4.2 Parasite results 26 4.5 Skipjack Migration 31 4.6 Fishery Interactions 32 4.7 Skipjack Population Dynamics 4.8 Yellowfin 35 5.0 CONCLUSIONS 37 39 REFERENCES
APPENDICES A. Scientists, observers and crew on board the research vessels 45 B. Bait species, percentage of bouki-ami hauls containing VI
a particular species, and estimated total catch, for the Skipjack Programme survey in the waters of Tonga 47 Details of tagged fish known to have made international migrations into or out of Tonga 49 Results of skipjack tagging in Tonga and the surrounding areas of Fiji, Wallis andFutuna, Western Samoa, American Samoa and Niue (as of October 1982) 51 Abbreviations for countries, territories and subdivisions thereof 53 vii
LIST OF TABLES
Table Page
1 Summary of daily field activities in the waters of Tonga ^
2 Summary of baitfishing activities in the waters of Tonga 9
3 History of baitfishing in Tonga *•"
4 Effort and catch results for baitfishing techniques commonly used by the Skipjack Programme 12
5 Estimated commercial tuna catches by the Skipjack Programme in Tonga 1^
6 Total tuna catches and average daily catches by joint venture skipjack pole-and-line vessels in Papua New Guinea, Solomon Islands, Fiji and Palau 15
7 Surface tuna schools sighted in Tonga 16
8 Summary of numbers of fish sampled for biological data from the waters of Tonga 16
9 ' Diet items found in the stomachs of skipjack sampled in the waters of Tonga 1?
10 ' Incidence of tuna juveniles in the stomachs of skipjack and other species from the waters of Tonga 21
11 Summary of skipjack growth increments by visit for fish at liberty from 10 to 365 days 23 12 Calculated growth increments for fish recaptured within country of release 22
13 Skipjack tag release/tag recovery matrix for all tag releases and for all tag recoveries received by the Programme as of 16 December 1982 27
14 Summary of fishery interactions between local fisheries 27
15 Skipjack population parameters and 95 per cent confidence limits estimated from aggregate tag returns 33
16 Comparison of skipjack and yellowf in movement -*7 Vlll
LIST OF FIGURES
Figure Page
The area of the South Pacific Commission Inside front cover
Straight line representations of movements of Inside back skipjack tagged by the Skipjack Programme and cover subsequently recovered
Monthly commercial skipjack catch in Tonga (January 1978-April 1981) by pole-and-line gear 3
Survey area and baitfishing localities for the 1978 and 1980 Skipjack Programme surveys in the Kingdom of Tonga 1
Length frequency distributions for skipjack sampled in the waters of Tonga 19
Distribution of female skipjack by maturity stage for samples from Tonga and for all skipjack sampled by the Skipjack Programme from tropical waters 20
Skipjack serum esterase gene frequency for 163 samples from individual skipjack schools, versus longitude of the sample location 25
Numbers of skipjack tag recoveries by distance travelled and time-at-large for the total Skipjack Programme data set 28
Straight line migration arrows for tagged skipjack released in Tonga and recaptured in other areas, and for tagged skipjack released in other areas and recaptured in Tonga 29
Migration arrows for 80 of 2,139 recoveries of skipjack tagged in the waters of Tonga, Fiji, Wallis and Futuna, Western Samoa, American Samoa and Niue 30
Number of skipjack tag recoveries versus months at large 34
10 Length frequency distribution for yellowfin sampled in the waters of Tonga 35
11 Straight line representation of movements of yellowfin tagged by the Skipjack Programme and subsequently recovered 36 AN ASSESSMENT OF THE SKIPJACK AND BAITFISH RESOURCES OF THE KINGDOM OF TONGA
1.0 INTRODUCTION
The Skipjack Survey and Assessment Programme was created in response to rapid expansion of surface fisheries for skipjack (Katsuwonus pelamis) during the 1970s in the waters of the central and western Pacific. The objectives of the Skipjack Programme were to survey the skipjack and baitfish resources within the area of the South Pacific Commission, and to assess the status of the stocks and the degree of interaction between fisheries for skipjack within the Commission region and beyond. The assessments were designed to provide the countries and territories of the region with a basis for rational development of skipjack fisheries and sound management of the resource.
Tagging and survey operations by the Skipjack Programme in the central and western Pacific totalled 847 days between October 1977 and August 1980. The study area included all countries and territories in the area of the South Pacific Commission and the waters of northern New Zealand and eastern Australia (Figure A, inside front cover). During two surveys, 30 days were spent in the waters of Tonga. Preliminary results of the first survey in Tonga have previously been reported by Kearney and Gillett (1978).
This report presents final results of the work of the Skipjack Survey and Assessment Programme in the waters of Tonga from 11 April to 3 May 1978 and from 3 to 9 March 1980. Results from both surveys, together with data from other sources and from adjacent areas where the Skipjack Programme carried out research, are used to assess the skipjack and baitfish resources of Tonga and to evaluate their potential for development.
1.1 Description of the Fishery
Skipjack fishing does not presently play a major role in the Tongan economy. In 1980 it was estimated that the combined total of all fish caught in the Kingdom was approximately 2,000 tonnes, of which less than two per cent was skipjack. However, officials of the Tonga Fisheries Division believe that skipjack comprises half of the potential annual yield of all of the Kingdom's fisheries resources (Ratcliffe et. &1_. 1981). They estimated that the demand for fish was much greater than the supply in 1981, and that this demand will increase to 4,000 tonnes per year before 1985. At present there is considerable fishing effort expended on inshore fish stocks but no substantial increase in their catch is foreseen. As the stated goal of fisheries development in Tonga is to increase fish production to the level of maximum sustainable yield in the most economically efficient manner possible (Ratcliffe .et. iLL* 1981), skipjack resources should play an important role in Tonga's future. Ratcliffe et_ al. (1981) estimate that the potential annual skipjack catch from the waters of Tonga is at least 10,000 tonnes.
Traditional skipjack fishing in Tonga was carried out using canoes and pearl-shell lures, typical of the traditional methods of many areas of Polynesia. During the period of the Skipjack Programme, Tongan fishermen caught skipjack by trolling pearl-shell lures from motorised launches and by live-bait fishing from two bait boats. One of these vessels, the 15-metre Kahikahi. is a converted shrimp trawler, and the other, the Takuo, 2
is a conventional, but relatively small (16.5 metres) Japanese pole-and-line boat. Monthly catches from these vessels (C. Ratcliffe, personal communication) for the period January 1978 to April 1981 (Figure 1) show highest catches occurring in the warmer months, October through March.
Some skipjack are caught in the waters of Tonga by vessels registered in Asian countries. Between 1972 and 1978 the Japanese pole-and-line fleet spent a total of 23 boat days in Tonga and caught 77 tonnes of skipjack, 2 tonnes of yellowfin and 2 tonnes of bigeye, giving an average of 3.5 tonnes per boat day (Skipjack Programme 1980). The most recent, complete data for Korean and Taiwanese longliners show that in 1976 these vessels made an incidental skipjack catch of 1.2 tonnes, while landing 816 tonnes of mainly larger tuna species (Klawe 1978). According to published data, longline vessels from Japan have not operated in the waters of Tonga since 1973 (Skipjack Programme 1981f). Estimates of Taiwanese and Korean longline catches in more recent years (Simiki, Ratcliffe and Sorrenson 1981) suggest that the present annual skipjack catch in Tonga by longlining is only three to four tonnes.
1.2 Previous Surveys
In 1951, the Department of Agriculture conducted a survey of skipjack fishing in Tonga by- interviewing fishermen (Vaea and Straatmans 1954; Williams 1969). The following year a fisheries officer post was established within the Government and experimental tuna and bait fishing was done by this officer in 1954 (Van Pel 1956). In 1955, Van Camp Sea Food Company investigated the pelagic fish resources around Tonga (B. Fink, personal communication), and in the same year the South Pacific Commission conducted a general investigation of fisheries (Van Pel 1956; Williams 1969). Kyokuyo Hogei Co. Ltd. conducted a marine resources survey in April and May 1965, which included some exploratory baitf ishing (Anon 1969). A United Nations Development Programme/Food and Agricultural Organization (UNDP/FAO) tuna mission visited Tonga in 1969 (Anon 1969). In the period 1970 to 1974, there were four Japanese skipjack and baitfish surveys in Tongan waters (Anon 1973; Wilkinson 1974; T. Fusimalohi, personal communication). For 20 months, beginning in July 1975, an FAO project studied demersal fish, skipjack and baitfish resources in Tonga (Thomas 1978). On one day in July 1979 and on one day in September 1979, the French research organisation Office de la recherche scientifique et technique outre-mer (ORSTOM) carried out aerial spotting for tuna in the 200-mile zone of Tonga while operating from neighbouring Wallis and Futuna Islands (Marsac 1981).
There are no records of tuna purse-seining in the waters of Tonga. In recent years this fishing technique has been used successfully throughout most of central and western tropical Pacific. The possible future importance of seining to Tonga is highlighted by Ratcliffe .§_£ a_l. (1981), who state that the development of a successful tuna fishery in Tonga would require the introduction of purse-seining.
2.0 METHODS
2.1 Vessel and Crew
Two commercial fishing vessels were used by the South Pacific Commission's Skipjack Programme for surveys in the waters of Tonga. The FIGURE 1. MONTHLY COMMERCIAL SKIPJACK CATCH IN TONCA (JANUARY 1978-APRIL 1981) BY GEAR
20000
15000-
I o 10000 < O
o < o Q. 5000
0 0 °'°- .© '••' °-. • • . : 0-- T T I T - T©-t®1 7 T r ! I I T" T©T T -•l'&T&T©r T T^T^T^T T "I""rO I ' I Q~1 [0 1978 1979 1980 YEAR 4
Hatsutori Maru No.l of 192 gross tonnes was used for the first survey and the Hatsutori Maru No.5 of 254 gross tonnes was used for the second. Both vessels were chartered from a commercial fishing company, Hokoku Marine Products Company Limited, Tokyo, Japan, and were slightly modified to accommodate the requirements of fisheries research work. Details of both vessels are given in Kearney (1982b).
The Hatsutori Maru No. 1 operated with at least three Skipjack Programme scientists, nine Japanese officers and twelve Fijian crew. For the Hatsutori Maru No.5. an additional three Fijian crew were employed. Representatives from the Tongan Fisheries Department participated in the survey, and were on board for varying periods of time. Lists of all personnel and details of the times scientists and observers spent on board are given in Appendix A.
2.2 Research Plan
Visual scanning and exploratory fishing for tunas and baitfish were the primary survey techniques. Tagging and biological sampling, including skipjack blood and parasite studies, were the basic tools for the study of skipjack and yellowfin resources. Comparison of results from other areas in the central and western Pacific visited by the Skipjack Programme to those obtained in Tonga, analysis of previous work in Tonga, and examination of trends in the local fishery form the basis of this resource assessment.
2.3 Skipjack Fishing and Tagging
The Skipjack Programme used two modified Japanese commercial live-bait pole-and-line vessels during the surveys in Tonga. The basic strategy of spotting, approaching and chumming schools normally employed by these vessels was not changed, although minor variations in technique were tried from day to day depending upon the behaviour of skipjack schools, and on the quantity and quality of live bait carried.
The number of crew on both the Hatsutori Maru No. 1 and the Hatsutori Maru No.5 was less than these vessels carry under commercial fishing conditions. As at least one crew member was required to assist each scientist in the tagging procedures, the effective number of fishermen was further reduced. Additionally, the need to pole skipjack accurately into the tagging cradles reduced the speed of the individual fishermen. In 1978, during the Skipjack Programme's survey of the waters of Fiji, the relative fishing power of the Hatsutori Maru No.l was calibrated by comparing the vessel's performance under survey conditions to the performance of the commercial fleet operating in the same area at the same time, and also by comparing the performance of the vessel under survey conditions to its performance in the one-month period during which it fished under commercial conditions with the same captain and enlarged crew. It was determined that an appropriate factor for converting survey catches to estimated commercial catches was 3.47 for the Hatsutori Maru No. 1 (Kearney 1978). It was assumed that this conversion factor also applied to the Hatsutori Maru No.5.
As tagging was the primary tuna research tool, attempts to tag large numbers of fish often dominated the fishing strategy. At other times, purely exploratory fishing was the primary concern. The tagging technique and alterations to normal fishing procedures are described in detail in Kearney and Gillett (1982). 5
2.4 Biological Sampling
A record of all fish schools sighted throughout the survey was maintained. Where possible, the species composition of each school was determined and records were kept of schools chummed and their subsequent biting response. Specimens of tuna and other pelagic species which were poled or trolled, but not tagged and released, were routinely analysed. Data collected include length, weight, sex, gonad weight, stage of sexual maturity, and stomach contents. Diet items resembling tuna juveniles were retained in preservative and periodically sent to ORSTOM in Noumea for identification to genus and species. Argue (1982) discusses the biological sampling methods in detail.
Blood samples for subsequent genetic analysis were collected according to the methods described by Fujino (1966) and Sharp (1969). Samples were frozen, packed in dry ice, and air freighted to the Australian National University, Canberra, .Australia, where they were electrophoretically analyzed according to the methods described by Richardson (1983).
During the second Tongan survey, skipjack body cavities were examined for the presence of macro-parasites, and five complete sets of gills and viscera from a maximum of three schools per day were frozen and subsequently air freighted to the University of Queensland, St Lucia, Australia, for detailed examination for the presence of parasites.
2.5 Baitfishing
Baitfishing was carried out by the Programme in the waters of Tonga using a "bouki ami" net set at night around bait attraction lights or by beach seine during the day. Night baiting procedures were similar to those used by commercial vessels operating in Papua New Guinea, Solomon Islands, and Fiji, but were modified where necessary to meet the Programme's special requirements. The beach seining method was modified from that used by commercial vessels in Hawaii. Details of both techniques and all modifications employed are given in Hallier, Kearney and Gillett (1982).
2.6 Data Compilation and Processing
Five separate logbook systems were used aboard ship for compiling data gathered during Skipjack Programme fieldwork. Descriptions of the logbooks are given by Kearney (1977), Argue (1982), Kearney and Gillett (1982) and Hallier, Kearney and Gillett (1982). Data from the logs were entered into the Programme's Hewlett Packard 1000 computer system in Noumea. The techniques used in entering and processing the data are discussed by Kleiber and Maynard (1982). Electrophoretic characteristics of all the blood samples collected and analysed at the Australian National University, and parasite identifications of all viscera specimens taken and analysed at Queensland University, were also entered into computer files.
2.7 Data Analysis
Assessment of the skipjack resource and possible interactions among skipjack fisheries was approached from several viewpoints. Studies of the migration of tagged skipjack, using analytic techniques described in Skipjack Programme (1981a), formed the basis of investigations of movement patterns and fishery interactions. Evaluation of the magnitude of the skipjack resource and its dynamics, based on tagging data, are described in 6
Kleiber, Argue and Kearney (1983). Methods employed in biological studies of growth are described in Lawson and Kearney (MS) and Sibert, Kearney and Lawson (1983), and of juvenile abundance, in Argue, Conand and Whyman (1983). Procedures used to compare fishing effectiveness between different baitfish families are described in Skipjack Programme (1981e) and Argue, Hallier and Williams (MS). Evaluation of population structuring across the whole of the western and central Pacific has centred on a comparison of the tagging results with the blood genetics work (Anon 1980, 1981; Skipjack Programme 1981b). Occurrence and distribution of skipjack parasites have also been evaluated (Lester 1981).
3.0 SUMMARY OF FIELD ACTIVITIES
During 30 days in the waters of Tonga the two research vessels travelled approximately 3,000 nautical miles while surveying a large area for tuna and baitfish (Figure 2). The Programme spent 17 days fishing for skipjack, 3 days baiting, 7 days travelling and 3 days in port (Table 1). The Vava'u, Tongatapu and Ha'apai island groups were surveyed, as were some outlying islands in the extreme north and south of Tonga.
The research vessels fished for bait on 44 occasions, and caught a total of 1,287 kg of live bait. With this bait, 9,713 kg of skipjack and other tunas were caught. A total of 2,231 skipjack and yellowfin tuna were tagged and released (Table 1); 13 skipjack and one yellowfin have since been recovered (to December 1982). A single skipjack blood sample of 95 specimens from a single school was collected on 21 April 1978.
4.0 RESULTS AND DISCUSSION
• 4.1 Baitfish
A detailed account of the Skipjack Programme baitfishing results appears in Table 2 and a summary of results from 10 different baitfishing projects in Tonga spanning 26 years (1954-1980) is presented in Table 3.
Major factors to consider when evaluating a baitfishery are the quantity of bait available to the fishery, the effectiveness of this bait, and the consistency of the supply. The following discussion focuses on the baitfish resources of Vava'u, the northern island group, since most baitfishing has taken place amongst these islands. However, many of these findings are applicable to the other island groups (Tongatapu, Ha'apai).
4.1.1 Quantity of bait
Information on the quantity of bait caught by various vessels in Tonga is given in Table 3. Average catches for a 24-hour period have ranged between 18 and 99 kg for night baiting and between 14 and 58 kg for day baiting. Two anomalies in Table 3 should be noted. Firstly, the highest catches were obtained by the Tonga Fisheries Division vessels, Hakula and Takuo. However, examination of data in Gibson (1981) shows that these two vessels fished an average of only 5.2 and 4.1 nights per month respectively between July 1978 and April 1980, primarily when the moon phase was most favourable. Secondly, Skipjack Programme baiting during the 1980 survey in Tonga took place just prior to the full moon when bait attraction lights are much less effective; accordingly, Programme catches were reduced. 7
FIGURE 2. SURVEY AREA AND BAITFISHING LOCALITIES FOR THE 197 8 AND 1980 SKIPJACK PROGRAMME SURVEYS IN THE KINGDOM OF TONGA
177W 170W 17SW 174W 173W 172W
8
R
VAVA'U '*
&
^ 0 .HA'APAI
1
*
TONGATAPU * & SURVEY AREA 111 BAITING LOCATIONS * 177W 170W 170W 174W 173W 172W TABLE 1. SUMMARY OF DAILY FIELD ACTIVITIES IN THE WATERS OF TONGA. Schools sig SJ=skipjack or skipjack with other species except yellowfin, YF=yellowfin or except skipjack, S+Y=skipjack with yellowfin or skipjack with yellowfin a species without skipjack or yellowfin, UN=unidentified, but most likely schoo School s Sight ed Fis h Tagged Principal Bait Hours (number s) (numbers) Date General Area Activity Carried Fishing SJ YF S+Y OT UN SJ YF OT (k«) 11/04/78 NW of Tongatapu Fishing 264 10 0 0 1 0 3 299 5 0 12/04/78 Tongatapu Fishing 189 4 0 0 1 0 1 155 17 0 13/04/78 Tongatapu Fishing 116 8 1 0 1 0 2 35 23 0 14/04/78 Tongatapu - Steaming 30 3 1 0 0 0 5 0 0 0 Ha'apai 15/04/78 Vava'u Steaming 0 0 ------16/04/78 Vava'u Fishing 15 3 1 0 0 0 0 54 0 0 17/04/78 Vava'u Fishing 47 3 0 0 1 0 0 126 0 0 18/04/78 Vava'u Fishing 96 7 3 0 1 0 2 34 20 3 19/04/78 Vava'u Fishing 96 10 1 0 2 0 0 77 66 0 20/04/78 Vava'u Fishing 20 5 1 0 0 1 0 0 0 0 21/04/78 Vava'u Fishing 63 6 3 0 1 0 0 63 30 0 22/04/78 Vava'u In Port 0 0 ------23/04/78 Vava'u In Port 0 0 ------24/04/78 Vava'u Baiting 48 0 ------25/04/78 Vava'u Fishing 59 4 1 0 1 0 0 144 23 0 26/04/78 Vava'u Baiting 53 0 ------27/04/78 Vava'u Fishing 81 9 3 0 2 0 1 48 20 0 28/04/78 Vava'u Baiting 72 0 ------29/04/78 Vava'u-Ha'apai Fishing 272 11 0 0 0 2 1 0 0 0 30/04/78 Ha'apai - Fishing 174 9 0 0 4 0 1 367 54 0 Tongatapu 01/05/78 Tongatapu In Port 0 0 ------02/05/78 Tongatapu - Steaming 0 3 0 0 0 0 0 ** — — Ha'apai 03/05/78 Vava'u-Niuafo'ou Steaming 0 11 0 0 0 0 2 - - - 03/03/80 Vava'u Steaming 0 8 1 0 0 0 13 - _ - 04/03/80 Vava'u Fishing 21 3 1 0 0 0 4 71 0 0 05/03/80 Vava'u Fishing 99 8 4 4 1 0 3 239 4 0 06/03/80 Vava'u Fishing 89 4 2 2 0 0 2 179 0 0 07/03/80 Vava'u Fishing 95 7 1 1 0 0 7 78 0 0 08/03/80 Vava'u-Ha'apai Steaming 108 10 2 0 0 1 17 0 0 0 09/03/80 S of Tongatapu Steaming 101 12 0 0 0 0 0 0 0 0 TOTALS 158 26 7 16 4 64 1969 262 3 9 TABLE 2. SUMMARY OF BAITFISHING ACTIVITIES IN THE WATERS OF TONGA Time Number Est. Av. of of Catch Mean Anchorage Hauls Hauls Dominant Species* per Haul Length Other Common Species* (kg) (mm) Nuku'alofa Hbr Sardinella sirm 54 114 Pranesus pinguis 21°08'S Night 1 Gazza minuta 5 Herklotsichthvs punctatus 175'10'W Scomberoides sp. 3 105 Dussumieria acuta Nuku'alofa Hbr Pranesus pinauis 7 Dactyloptera orientalis 21°09'S Night 2 Sardinella sirm 1 Sp. of Priacanthidae 175°11'W Spratelloides delicatulus Mullodichthvs sp. Nuku'alofa Hbr Scomberoides sp. 2 Sp. of Priacanthidae 2r07'S Night 1 Spratelloides delicatulus 2 Selar crumenophthalmus 175°10'W Dussumieria acuta Vaimalo Spratelloides delicatulus 11 42 Stolephorus devisi 18°38'S Night 12 Pranesus pinjtuis 8 84 Herklotsichthvs punctatus 174°00'W Hypoatherina ovalaua 4 63 Selar crumenophthalmus Koko Stolephorus devisi 16 55 Pranesus pinguis 18°39'S Night 12 Atule mate 11 109 Spratelloides gracilis 173°59'W Hypoatherina ovalaua 2 68 Spratelloides delicatulus Tapana Island Pranesus pineuis 9 Selar crumenophthalmus 18°42'S Day 8 Hypoatherina ovalaua 3 Sp. of Synodontidae 173°59'W Spratelloides delicatulus 2 Caranx sp. Pangai Motu Pranesus pinguis 11 Caranx sp. 18°40'S Day 2 Hypoatherina ovalaua 6 Sp. of Tetrodontidae 174°01'W Spratelloides delicatulus 1 Mullodichthvs samoensis Fangai Motu Pranesus pineuis 8 Caranx sp. 18°40'S Day 2 Hypoatherina ovalaua 4 Sp. of Tetrodontidae 174°00'W Spratelloides delicatulus 1 Mullodichthvs samoensis Neiafu Hbr Selar crumenonhthalmus 21 124 Hvpoatherina ovalaua 18°40'S Night 4 Herklotsichthvs punctatus 10 77 Pranesus pinguis 173°59'W Sardinella sirm 8 119 Spratelloides delicatulus * Several recent revisions of scientific names used in a previous Skipjack Programme report on Tonga have been maintained. The most notable changes in nomenclature have been : Herklotsichthvs punctatus to Herklotsichthvs auadrimaculatus Pranesus pinguis to itherinomorus lacunosa Explanatory Notes Anchorage : Recorded positions are truncate d to the nearest minute. For large bays there may be more than one position tabu lated. Number of Hauls : Number of hauls at the anchorage position. A haul is defined as any time the net was placed in the water. Dominant Species : Those species that made up at .east one per cent of the numbers caught from one or more bait hauls at a particular location, ranked on their weighted proportion of the catch. Average Catch ( species) : The average catch in kilograms per haul is given f or dominant species for each anchorage and, gear type. This average catch is the product of the total catch in kilograms for the particular anchorage and gear type and the weighted proportion of the particular species in this catch. The weighted proportion of each species was determined from the numerical proportion in the catch multiplied by the cube of the mean standard length for that species, anchorage am gear type, and by a scaling factor. The scaling factor was chosen so that the sum of weighted proportions would equal the sum of numerical proportions. If the mean standard length was unknown, the numerical proportion was used Since the average catch per haul is given for only the dominant three species, the total of these is in general less than the total catch for the anchorage and gear type Mean Length : Weighted by numerical abundance when there were multiple hauls at the same location. 10 TABLE 3. HISTORY OF BAITFISHING IN TONGA Vessel Date Gear and Comment Time No. of Total Kg. Species* Source (Agency) days or Kg. per nights day or night Albatross Dec. 1900 Beach seining for specimen collec Day Tongatapu 1 ? 1 Mostly Mugilidae Alexander 1902 (U.S. Fish tion Day Nomuka 1 ? 1 Hemirhamphidae Commission) Day Vava'u 1 1 ? Various (Tonga Fisheries Mid-1954 Beach seining - Large fish captured Night ? 7 7 Large Selar sp. Van Pel 1956 Division) at night with lights; baitfish were Caranx sp. almost non-existant in catches Rastrelliger sp. SuruKU Maru No.l April-May Bouki-ami - Bait shown to be avail Night Vava'u ? ? 1 Sardine 11a SD. Anon 1969 (Kyokuyo Hogei Ltd. ) 1965 able but no account of distribu Atherinidae Williams 1969 tion or abundance Herklotsichthvs Ratcliffe punctatus et al. 1981 Kuroshio Maru No.l Dec. 1972 Bouki-ami - Tongatapu and Ha'apai Night Vava'u 1 29 29 Atherinidae Anon 1973 (JAMARC) prospected but net not hauled Ha'apai Herklotsichthvs Tongatapu punctatus Akitsu Maru No.20 Dec. 1973- Bouki-ami and dip net, set net Night Vava'u 31 568 18 Spratelloides Wilkinson 1974 (JAMARC) Jan. 1974 delicatulus Anon 1974 Selar sp. Apogonidae Trooac. FAO-70. Aug.-Oct. Sampling only with 16 sq. ft. Night Tongatapu ? ? 11 Spratelloides Thomas 1978 Kahikahi (FAO) 1975 dip net Ha'apai delicatulus Atherinidae Herklotsichthvs punctatus Mar. 1976- Lift net operated from bait Night Vava'u 24 1374 57 Atherinidae Thomas 1978 May 1977 barge for night baiting, Herklotsichthvs 40 fathom x 2 fathom beach punctatus net for day baiting Selar sp. Spratelloides delicatulus Day Vava'u 22 577 26 Atherinidae Herklotsichthvs w punctatus Spratelloides delicatulus Kahikahi Jan. 1977- Lift net Night Vava'u 68 4503 66 Atherinidae Gibson 1981 (Tonga Fisheries Feb. 1978 Herklotsichthvs Division) punctatus Spratelloides delicatulus Stolephorus sp. Hakula July 1978- Lift net Night Vava'u 37 3428 93 Atherinidae Gibson 1981 (Tonga Fisheries Jan. 1979 Herklotsichthvs Division) punctatus Spratelloides delicatulus Stolephorus sp. Takuo July 1978- Bouki-ami Night Vava'u 58 5768 99 Atherinidae Gibson 1981 (Tonga Fisheries April 1980 Herklotsichthvs Division) punctatus Spratelloides delicatulus Stolephorus sp. Hatsutori Maru April-May Bouki-ami and 148 m beach seine Night Vava'u 16 695 43 Atherinidae Kearney and No.l (SPC) 1978 Tongatapu Spratelloides Gillett 1978 delicatulus Selar sp. Day Vava'u 3 176 58 Atherinidae Spratelloides delicatulus Hatsutori Maru Mar. 1980 Bouki-ami and (148+80 m) beach Night Vava'u 5 396 80 Spratelloides No.5 (SPC) seine delicatulus Atherinidae Herklotsichthvs punctatus Day Vava'u 1 14 14 Spratelloides delicatulus Atherinidae AVERAGES Day 29.5 kg TOTALS Day 26 767 Night 69.8 kg Night 240 16761 * Several recent revisions of scientific names used in a previous Skipjack Programme report on Tonga have been maintained. The most notable changes in nomenclature have been : Herklotsichthvs punctatus to Herklotsichthvs auadrimaculatus Pranesus pinsuii to Atherinomoru s lacunosa 11 Average catches for all baitfishing operations listed in Table 3 were 69.8 kg per night of fishing and 29.5 kg per day of fishing. To put these figures into perspective, they can be compared to Skipjack Programme catches in other survey areas. Table 4 shows the bait catches made by the Programme in 26 countries, territories and subdivisions thereof. Factors affecting the success of baitfishing can be expected to vary somewhat between countries and through time, and therefore limit the value of detailed comparisons between countries. Nonetheless, information from neighbouring areas is still useful in a general sense to help gauge baitfishing potential. Table 4 shows that the total catch in Tonga, although not insignificant, was considerably less than that taken by the Skipjack Programme in other countries where there have been commercial bait fisheries (Papua New Guinea, Solomon Islands, Fiji and Palau). The Programme's average catch per bouki-ami haul in Tonga, 34 kg, was second lowest of all countries where bouki-ami baitfishing was attempted. Further comparison can be made with the Papua New Guinea commercial fishery, where for profitable fishing a 20-metre pole-and-line vessel has been estimated to require over 90 kg of bait a night, and would need to catch bait 28 nights each month (Kearney 1975). These comparisons suggest that baitfish catches taken in Tonga by the Skipjack Programme and other survey vessels were marginal for commercial operations. From an FAO study (Thomas 1978), it was estimated that in Vava'u it would be possible to capture 286 kg of bait per 24-hour period, 15 days a month, for four months a year (i.e. 17,000 kg a season). Thomas recommended use of four night-baiting barges and three day-baiting crews to obtain this catch. Although previous average daily catches suggest this might be possible, it is questionable whether using seven different operations would be practical from a logistic or economic viewpoint. Nevertheless, the use of more than one baiting technique to gather adequate quantities of live bait for fishing operations appears necessary to maximise catches. 4.1.2 Baitfish effectiveness The effectiveness of baitfish species for pole-and-line fishing depends on their survival in the bait tanks after capture and their ability to stimulate tuna to bite. Gold anchovy (Stolephorus devisi). hardyheads (Atherinidae), blue sprat (Spratelloides delicatulus). and gold spot herring (Herklotsichthvs punctatus) dominated the total baitfish catch in Tonga (Tables 2 and 3; Appendix B); however, gold anchovy only occurred in 6 of 32 hauls. Sprats survived well in the bait tanks, as did mollies; both averaged less than 10 per cent mortality per day (Skipjack Programme 1981e). Hardyheads did not survive well (27% daily mortality), but were stronger than the herring and gold anchovies (>42% daily mortality) (Skipjack Programme 1981e). In Tonga, both the Skipjack Programme and FAO surveys recorded baitfish mortalities of approximately 20 per cent per day. The Skipjack Programme tuna:bait ratio (kg tuna caught to kg bait chummed) in Tonga was 7.6:1 under survey conditions, whereas the FAO survey obtained a 20:1 tuna:bait ratio. The Programme's ratio would undoubtedly have been higher had the vessel been fishing commercially, although probably somewhat less than 26:1, which is the product of the survey tuna:bait ratio and the 3.47 survey catch to commercial catch conversion ratio. Based on several indices of fishing effectiveness, the Skipjack Programme concluded that of the baitfish species considered throughout the total survey area, hardyheads, along with cultured mollies, were least attractive to tunas, whereas sprats and gold spot herring were both TABLE 4. EFFORT AND CATCH RESULTS FOR BAITFISHING TECHNIQUES COMMONLY USED BY T Results from Skipjack Programme (1981d). B 0 U K I - A M I B E No. of No. of Baiting Average Baiting Localities No. of Total Loaded Catch Localities No. o Fished Hauls Catch Catch per Haul Fished Hauls (kg) (kg) (kg) *Papua New Guinea 26 57 6,840 5,323 120 2 4 *Solomon Islands 24 60 8,965 8,406 148 0 0 New Caledonia 14 40 5,207 4,778 130 0 0 *Fiji 26 71 12,821 12,134 180 1 1 Vanuatu 3 5 177 177 35 0 0 Western Samoa 5 14 1,130 1,067 80 0 0 Society Islands 7 27 893 767 33 3 8 Marquesas Islands 6 44 5,601 5,367 127 4 34 Tuamotu Islands 3 27 1,196 1,051 44 0 0 Kiribati 5 21 1,198 1,155 57 3 7 Tonga 6 32 1,097 1,085 34 3 12 *Palau 9 34 3,310 2,996 97 0 0 *Ponape 3 36 5,056 4,534 140 0 0 Niue 0 0 0 0 - 0 0 Cook Islands 3 15 585 489 39 0 0 American Samoa 4 5 180 138 36 0 0 Marshall Islands 5 8 609 567 76 2 4 Yap Islands 1 2 258 255 129 0 0 Wallis and Futuna 4 36 10,501 9,134 291 0 0 *Truk Island 4 8 690 672 86 1 1 Kosrae 2 10 807 598 80 0 0 Norfolk Island 0 0 0 - - 0 0 Tuvalu 6 15 1,508 905 100 0 0 Nauru 0 0 0 - - 0 0 Tokelau 0 0 0 - - 1 3 Pitcairn Islands 0 0 0 - - 0 0 TOTALS 166 567 68,629 61,598 121 20 74 * Areas where commercial bait fisheries have operated. 13 attractive to tunas, although not as attractive as anchovies (Skipjack Programme 1981e). 4.1.3 Consistency of baitfish supply Two important factors affecting long-term baitfish catches are the # degree of resilience of the baitfish populations to fishing pressure, and natural fluctuations in their abundance. The ability of the baitfish resource to sustain substantial catches is in turn greatly influenced by the size of the total habitat and the stock/recruitment characteristics of the individual species. The Skipjack Programme made 12 consecutive bouki-ami hauls at both Vaimalo and Koko baiting locations in Vava'u (Table 2) over a two-week period. During this relatively short period of exploitation there was no evidence of a decline in baitfish abundance, although average catches at both locations were quite low. In contrast, Gibson (1981) reported that each of five baitfishing stations in Vava'u became exhausted of bait within a few nights of fishing. Large natural fluctuations in abundance of Herklotsichthys punctatus , which was present in 68 per cent of the baitfish hauls in Tonga, have been documented in the Marshall Islands (Hida and Uchiyama 1977), and by the Skipjack Programme in the Gilbert group of Kiribati (Kearney and Gillett 1978). In Palau, the abundance of this species has declined markedly in apparent response to fishing pressure (Johannes 1981). In addition, Spratelloides delicatulus (which was found in 81 per cent of the baitfish hauls in Tonga) has been observed to undergo major changes in abundance in 0 Tuvalu (Ellway ^t. al_. 1983), and in the Cook Islands (Lawson and Kearney 1982). These observations suggest that large fluctuations in Tonga's bait supplies can be expected and baiting strategy therefore should be planned accordingly. 4.1.4 Ha'apai and Tongatapu Relatively poor bait catches were made by the Skipjack Programme at Tongatapu, by the Japanese at Ha'apai and Tongatapu (Anon 1973, 1974), and by FAO at Ha'apai (Thomas 1978). The relatively large size of the Hatsutori Maru No.l and No.5 and their requirement for water deeper than 20 metres for use of bouki-ami gear precludes baiting by this type of vessel in most areas of Ha'apai. A smaller vessel with a shallower net could bait at some locations in Ha'apai; however, the small size of the islands, bays and lagoons suggests that bait habitat and therefore bait abundance is not great. Seasonal variation in baitfish abundance is likely to be pronounced in the more southerly Tongatapu group since temperature variations between summer and winter are greater there. 4.1.5 Baitfish culture To alleviate the problem of bait shortages, a number of bait culture projects have been undertaken in Tonga. Trials with mollies were carried out in 1977 (Thomas 1978) and 1979 (Anon 1979), both times with inconclusive results. Additional baitfish culture trials are planned between 1982-84 (Ratcliffe et. ad. 1981). In addition to the work in Tonga, there have been at least eight baitfish culture projects using mollies or milkfish in other countries of the South Pacific Commission area. To date, none of these projects has 14 developed into a full-scale commercial venture. The economics of several of these baitfish culture operations are discussed by Kearney and Rivkin (1981). Their conclusions, experience from other countries, and Tonga's Own experience, do not engender optimism for the economic success of new projects in Tonga. 4.2 Fishing Success/Skipjack Abundance * A total of 9.71 tonnes of tuna were captured during the Programme's 17 fishing days in Tonga, for an average of 0.57 tonnes per day. Estimated commercial catches were 1.98 tonnes/day, using the survey catch to commercial catch conversion factor of 3.47 (Kearney 1978). These data, disaggregated by island group, are shown in Table 5. TABLE 5. ESTIMATED COMMERCIAL TUNA CATCHES BY THE SKIPJACK PROGRAMME IN TONGA Vava'u Ha''apai , Tongatapu April Days fished 9 4 1978 Tonnes per day 1.07 3.12 March Days fished 4 (insufficient 1980 Tonnes per day 2.91 data) The estimated commercial catch for the southern island groups averaged 3.12 tonnes/day, close to average daily catch rates by commercial pole-and-line vessels based in other Pacific island countries (Table 6). However, this figure is somewhat misleading when gauging local pole-and-line fishing potential since 90 per cent of the tunas in the southern island groups were caught with bait transported from Fiji and Vava'u. Additional information on commercial fishing success is available for Tonga. The Japanese pole-and-line fleet spent 23 days in the waters of Tonga in 1975, 1976 and 1977. Their average catch per boat day, 3.5 tonnes, although relatively low for this type of vessel, was higher than the overall catch rate achieved by the Skipjack Programme. However, in Tonga the Programme's research vessels were limited more by the low availability of live bait than by lack of tuna, a problem not experienced by Japanese long-range vessels which transport live bait from Japan. This problem is placed in perspective by considering that the optimistic estimate of annual bait catch for Vava'u (Thomas 1978), 17,000 kg, would be sufficient for an annual tuna catch of only 272 tonnes (assuming 20 per cent bait mortality and a tunarbait ratio of 20:1, Section 4.1.2). The number of tuna schools sighted provides additional information on abundance of vulnerable tunas in Tonga to pole-and-line gear (Table 7). Sighting rates averaged 0.80 over both surveys, but varied more than three fold between surveys. The average number of schools sighted per hour for all countries and territories visited by the Skipjack Programme was 0.75, similar to the average sighting rate in Tonga. There may be more seasonality to tuna abundance in Tonga (Figure 1), compared to countries in the SPC area which have established pole-and-line fisheries (Argue and Kearney 1982; Tuna Programme MS), due to Tonga's TABLE 6. TOTAL TUNA CATCHES AND AVERAGE DAILY CATCHES BY JOINT VENTURE SKIPJAC VESSELS IN PAPUA NEW GUINEA, SOLOMON ISLANDS, FIJI AND PALAU. (1981). Papua New Guinea Solomon Islands Fiji Av. Catch Av. Catch Av. Catch Total per Boat Total per Boat Total per Boat Total Year Catch per Day Catch per Day Catch per Day Catch (kg) (kg) (kg) (kg) (kg) (kg) (kg) 1970 2,430 4.76 8,534 1971 17,002 4,19 4,711 5.75 2,348 1972 13,124 2.67 7,885 2.35 2,243 1973 28,269 3.68 6,512 3.35 4,660 1974 41,780 4.40 10,331 4.74 7,374 1975 17,322 2.69 7,142 2.95 7,516 1976 33,035 4.23 15,787 4.52 702 2.2 4,318 1977 24,411 2.51 11,547 2.62 1,706 2.7 2,683 1978 48,933 4.92 17,353 3.69 2,524 3.1 N.A. 16 location in higher latitudes. Thus it is likely to be difficult for pole-and-line vessels based in Tonga to achieve the same annual catches as, for example, vessels based in Papua New Guinea or Palau where it is possible to fish all year. TABLE 7. SURFACE TUNA SCHOOLS SIGHTED IN TONGA Vava'u Ha'apai, Tongatapu April Hours searching/fishing 69 37 1978 Schools spotted per hour 0.43 0.57 March Hours searching/fishing 40 (insufficient 1980 Schools spotted per hour 1.65 data) 4.3 Biological Observations on Skipjack A summary of the number of biological samples collected in Tonga appears in Table 8. TABLE 8. SUMMARY OF NUMBERS OF FISH SAMPLED FOR BIOLOGICAL DATA FROM THE WATERS OF TONGA Total No. Total No. Total No. Examined Examined Total No. Total No. Examined for Stomach for Tuna Species Measured Weighed for Sex Content Juveniles Skipjack 432 245 262 118 198 Katsuwonus pelamis Yellowfin 94 78 82 61 69 Thunnus albacares Mackerel Tuna 5 5 5 5 5 Euthvnnus affinis Frigate Tuna 8 8 8 8 8 Auxis thazard Rainbow Runner 16 16 13 14 14 Elaeatis bipinnulatus TOTALS 555 352 370 206 294 4.3.1 Stomach contents Table 9 lists the food items found in the 118 skipjack stomachs examined by the Skipjack Programme in Tonga. The stomach contents were 17 TABLE 9. DIET ITEMS FOUND IN THE STOMACHS OF SKIPJACK SAMPLED IN THE WATERS OF TONGA Item Diet Item Number of Percentage No. Stomachs Occurrence Fish and Invertebrates 1 Chum from Hatsutori Maru 97 82.20 2 Fish remains (not chum) 40 33.90 3 Squid (Cephalopoda) 32 27.12 4 Alima stage (Stomatopoda) 23 19.49 5 Megalopa stage (Decapoda) 18 15.25 6 Aluteridae 17 14.41 7 Chaetodontidae 11 9.32 8 Acanthuridae 11 9.32 9 Synodontidae 11 9.32 10 Tuna juvenile (Scombridae) 10 8.47 11 Balistidae 10 8.47 12 Nomeidae 8 6.78 13 Decapterus sp. (Carangidae) 8 6.78 14 Unidentified fish 8 6.78 15 Holocentridae 7 5.93 16 Priacanthidae 6 5.08 17 Stomatopoda 6 5.08 18 Empty stomach 5 4.24 19 Ostraciidae 5 4.24 20 Shrimp (Decapoda) 5 4.24 21 Lutjanidae 4 3.39 22 Dactvlopterus orientalis (Dacvlopteridae) 3 2.54 23 Crustacea 3 2.54 24 Xiphasia sp. (Xiphasiidae) 2 1.69 25 Gempylidae 2 1.69 26 Siganidae 2 1.69 27 Crustacean remains 2 1.69 28 Carangidae 2 1.69 29 Argonauta (Cephalopoda) 2 1.69 30 Amphipoda 2 1.69 31 Juvenile fish 2 1.69 32 Diodontidae 2 1.69 33 Tetrodontidae 2 1.69 34 Cigarette material 0.85 35 Gobiidae 0.85 36 Sternoptychidae 0.85 37 Fistulariidae 0.85 38 Paralepidae 0.85 39 Sphyraenidae 0.85 Total Stomachs Examined 118 18 typical of other tropical waters in the South Pacific Commission region. Besides chum from the Hatsutori Maru. 36 different food items were found in skipjack stomachs from Tonga. Fish remains, squid (Cephalopoda), the alima stage of stomatopods, the megalopa stage of decapods, and triggerfish (Aluteridae) were the most common food items and were each found in over 14 per cent of the stomachs examined. Analyses of feeding behaviour based on examination of items found in skipjack stomachs throughout the entire * region is currently in progress. 4.3.2 Skipjack size frequency The size frequency distributions of skipjack sampled in Tongan waters were quite different for each visit (Figure 3). The majority of skipjack sampled during the first visit were between 45 and 55 cm fork length; the modal length was 50 cm. Skipjack sampled during the second visit were considerably larger, ranging from 55 to 65 cm with a modal length of 60 cm. A previous survey captured skipjack averaging 80 cm (14 kg) from the waters of Tonga (Anon 1973). In contrast, Kearney (1973) states that in Papua New Guinea, skipjack above 6 kg (65 cm) are rare, far less than one per cent of the catch, and skipjack above 7 kg (69 cm) are almost never taken. 4.3.3 Sexual maturity and juvenile recruitment Information on female gonad maturity stages for skipj.ack sampled from Tonga is presented in Figure 4 for each survey (upper and middle graphs). Stages of gonad maturity were classified into seven categories representing a progression of reproductive condition from immature (stage 1) to post-spawning (stages 6 and 7). Maturing gonads are classified as stages 2 and 3, and mature gonads as stage 4. Ripe females are classified as stage 5. In both surveys late maturing and mature gonads (stages 3 and 4) were observed. Immature, early maturing (stage 2), and spent gonads were encountered only on the first survey. The absence of running ripe female gonads (stage 5) is not unusual; only two were found during the examination of 4,456 female skipjack from tropical waters surveyed by the Programme. The frequency of different female maturity stages for skipjack in Tonga is compared with that for female skipjack from all tropical waters surveyed by the Skipjack Programme (Figure 4, lower graph). It can be seen that the dominant maturity stages in Tonga correspond to the dominant maturity stages found in the much larger sample from tropical waters. An important aspect of the Skipjack Survey and Assessment Programme was an investigation of skipjack early life history and spawning activity through examination of stomach contents for juveniles. The number of tuna juveniles per 100 predators was considered to be an indicator of the relative abundance of tuna juveniles in a particular area. Table 10 summarises these results for Tonga. An average of 10.61 skipjack juveniles per 100 skipjack predator stomachs was observed. This level is intermediate between the high incidence of 25 to 50 juveniles per 100 stomachs found in Vanuatu, Wallis and Futuna, and the Marquesas Islands, and the low levels of zero to four juveniles per 100 stomachs found at the northern and southern extremes of the study area and in the Society Islands. Argue, Conand and Whyman (1983) discuss results of a region-wide study of occurrence of tuna juveniles in the stomachs of surface tunas. Data from their report suggest that Tonga is between two areas of relatively high juvenile skipjack abundance, one centred on the waters of Papua New Guinea, Solomon Islands and Vanuatu, and the other centred on the waters of the Marquesas and Tuamotu Islands in French Polynesia. 19 FIGURE 3. LENGTH FREQUENCY DISTRIBUTIONS FOR SKIPJACK SAMPLED IN THE WATERS OF TONGA. N is the sample size. 60 50H 1978 40 J-' N 300 30H 20 -•:i u < 10 Q. if) 25 Li- o 25-• ! Ld 1980 00 20 N 132 D 15 - J] V 10- \ . •• T ". • 1 1 n F^- 25 35 45 55 65 75 FORK LENGTH (cm) 20 FIGURE 4. DISTRIBUTION OF FEMALE SKIPJACK BY MATURITY STAGE FOR SAMPLES FROM TONGA (upper and middle graphs) AND FOR ALL SKIPJACK SAMPLED BY THE SKIPJACK PROGRAMME FROM TROPICAL WATERS (lower graph). N is the sample size. 40 TONGA - 1978 32 N 82 24 16 • i i i • i * i * i 12 3 4 5 6 7 JU' 24 TONGA - 1980 N 34 18- 12- 6 12 3 4 5 6 7 32001 ALL TROPICAL WATERS 2400 N 4456 1600 800 -r- 5 MATURITY STAGE o . <- TABLE 10. INCIDENCE OF TUNA JUVENILES IN THE STOMACHS OF SKIPJACK AND OTHER S WATERS OF TONGA Predators Prey No. of Predators Prey per 100 Predator Examined Species Prey with Prey Predators Skipjack 198 Skipjack 21 13 10.61 Frigate Tuna 11 10 5.56 Albacore 1 1 0.51 Thunnus sp. 1 1 0.51 Yellowfin 69 Skipjack 7 4 10.14 Frigate Tuna 1 1 1.45 Rainbow Runner 14 - Mackerel Tuna 5 - Frigate Tuna 8 - TOTALS 294 42 22 4.3.4 Growth The growth of skipjack, as in other tunas, is a function of size. The growth of larger fish, as measured by the rate of change in length, is slower than for smaller fish (Skipjack Programme 1981e). When a tagged fish is recovered, its increase in size depends on not only the length of time it was at liberty, but also its size when released. For a given time at liberty, a small fish will have a greater increase in length than a larger fish. These considerations complicate the evaluation of growth by the analysis of tagging data. Table 11 presents a summary of size and growth information for skipjack tagged and released in the study area, for each size class for which there were adequate data. Mean size at release varied from 41 cm to 55 cm; time at liberty varied from less than a day to over 300; growth increments varied from -0.3 cm to over 12 cm. The effects of time at liberty can be seen by noting the difference in growth increments calculated from tag release and recovery data generated by the two visits to Fiji (FIJI and FIJ2) where the fish were released at approximately the same size, but the mean times at liberty were quite different. Similarly, the effects of size at release can be seen by noting the difference in growth increments between the first visit to Kiribati (KIRl) and the second visit to Papua New Guinea (PNG2) where the fish were at liberty for approximately the same period of time, but the mean sizes at release were quite different. On the whole, growth increments were quite small and the percentage of fish which did not show any measurable growth was quite high (40.1%). There are several reasons for this apparent lack of growth. Firstly, the time at liberty may have been too short for much growth to have occurred. Secondly, skipjack may be near their maximum size when tagged and released. Thirdly, skipjack may have encountered conditions unfavourable for growth. Fourthly, errors in length measurement at both release and recovery may have obscured what little growth there was. ' Corrections for the effects of size at release and time at liberty on the observed growth increment were calculated using analysis of covariance and a linearised version of the von Bertalanffy growth equation. The corrections have been used to calculate a standard growth increment for an arbitrary size at release and time at liberty (Sibert, Kearney and Lawson 1983). Standardised growth increments are presented in Table 12. It can TABLE 12. CALCULATED GROWTH INCREMENTS (CM) FOR FISH RECAPTURED WITHIN COUNTRY OF RELEASE. Calculations for fish 50 cm in length at release and at liberty for 90 days. The 95% confidence interval of each increment given in parentheses. See Sibert, Kearney and Lawson (1983) for details. See Appendix E for abbreviations. Country Increment Visits Included FIJ 4.5 (+1.2) FIJI, FIJ2 KIR 1.4 (+1.2) KIRl PAL 8.5 (+6.4) PAL3 PNG 3.6 (+1.9) PNG2 PON 4.1 (+4.1) PON3 SOL 2.5 (+1.4) SOLI ZEA 1.5 (+5.2) ZEA1 TABLE 11. SUMMARY OF SKIPJACK GROWTH INCREMENTS BY VISIT FOR FISH AT LIBERTY FROM DAYS. Appendix E explains country abbreviations. RECAPTURES WITHIN Country N Mean Mean Mean Increment N Mean Mean and Sample Size at Size at Days at Standard Sample Size at Size at Visit Size Release Recapture Liberty Mean Deviation Size Release Recaptur FIJI 431 48.0 48.6 23.9 .65 2.29 3 51.3 55.3 FIJ2 208 51.2 55.3 108.7 4.09 5.34 9 51.7 61.3 KIR1 279 48.4 49.8 56.0 1.43 2.18 15 51.0 55.2 MAQ2 26 48.3 48.0 18.9 -0.27 1.31 3 48.0 60.0 PALI 0 14 59.0 63.1 PAL3 14 40.8 47.8 85.3 7.00 5.55 143 40.6 49.3 PNGO * 290 54.6 56.4 87.6 1.78 2.46 16 53.4 57.6 PNG2 609 54.6 55.2 51.5 0.63 3.17 37 51.5 56.8 PON1 7 53.9 57.7 84.7 3.86 2.67 12 53.9 57.6 PON3 13 51.4 57.2 168.0 5.77 2.31 43 55.4 59.9 SOLI 38 51.8 54.3 192.5 2.45 4.28 2 52.5 57.5 TRK1 1 50.0 56.0 121.0 6.00 - 10 49.7 56.7 TRK2 1 53.0 54.0 21.0 1.00 - 6 53.5 60.0 VAN1 1 52.0 52.0 0.0 0.00 - 3 50.7 57.3 WAL1 0 22 53.0 54.4 WAL2 0 7 52.9 57.1 WAL1+WAL2 0 29 53.0 55.0 ZEA1 213 45.8 46.4 37.9 0.64 2.30 11 47.5 54.2 ZEA2 1 54.0 54.0 76.0 0.00 ~ 3 50.3 57.7 * Results for skipjack tagged and released in Papua New Guinea from 1972 to 1974. 24 be seen that the amount of growth varied considerably from country to country. Further analysis shows that growth increments also differed significantly between visits to a country and between fish recovered inside and outside of the country of release (Sibert, Kearney and Lawson 1983). Skipjack growth is therefore seen to be highly variable in time and space. The observed growth in tagged skipjack is a function of where the fish were tagged, when they were tagged, and where they were recovered. Thus, growth of skipjack may be closely coupled to environmental conditions such as temperature and other oceanographic variables that are thought to regulate the abundance of food. The number of recaptures was insufficient to estimate skipjack growth for Tonga. 4.4 Population Structure 4.4.1 Blood genetics and tagging The Skipjack Programme investigated skipjack population structuring by collecting blood samples and simultaneously tagging skipjack from selected schools. During the fieldwork, blood samples were obtained from approximately 100 individuals from each of 58 schools throughout the study area; one of these schools was sampled in the waters of Tonga. To assist in the analysis and interpretation of these data, the Skipjack Programme hosted two workshops during which experts in the fields of fish genetics, population genetics, and fish population biology met with the Programme's scientists. Detailed results of the workshops are given in Anon (1980, 1981). Forty-two loci were surveyed for electrophoretically detectable polymorphisms (Richardson 1983) and serum esterase was considered most suitable for detailed consideration. In Figure 5 the gene frequency of serum esterase is plotted against the longitude of the location from which the samples were taken, with the sample from Tonga shown as an open circle. Esterase gene frequencies showed a pronounced longitudinal gradient across the study area, representing a decline in gene frequency from west to east, with a flattening of the gradient between French Polynesia and the eastern Pacific. The gene frequency for the single sample taken in Tonga is just above the regression line, and is within the 95 per cent prediction limits for the regression. Existence of the esterase gradient was considered (Anon 1981) to be strong evidence that there is some form of population structuring, and that Pacific skipjack do not comprise a single panmictic population in which all adults of a single generation have an equal chance of mating. Similarly, the flattening of the esterase gradient between French Polynesia, where there is thought to be extensive skipjack spawning (Argue, Conand and Whyman 1983), and the eastern Pacific, where spawning is limited (Klawe 1963), suggests that skipjack in the eastern Pacific could have been spawned in the central Pacific. Evidence that some skipjack move over much of the central and western Pacific (Figure B, inside back cover) indicates that genetic exchange is possible amongst all countries within the Programme's study area. Genetically isolated skipjack subpopulations separated by stable geographic boundaries were not consistent with these data. Furthermore, it was not possible to propose any permanent barriers to the interaction of FIGURE 5. SKIPJACK SERUM ESTERASE GENE FREQUENCY FOR 163 SAMPLES FROM INDIVID SCHOOLS, VERSUS LONGITUDE OF THE SAMPLE LOCATION. The circle represents gene frequency for the sample from Tonga. The regression line on the dotted line includes 145 samples collected between Indonesia and Pitc (correlation coefficient -0.81). Esterase gene frequencies for 18 eas samples are shown to the right of the dotted line. Results from Anon (198 u i 1 1 1 ' 1 •"•"•' i l 1 1 1 ' 1 o 9 z LU • D 8 a • Ld • • (Z \. •* • L_ 7 • * ^v ft " LU Z • UJ • 6 o • LU *• • • • • • (/) • ^^ < 5 • i > • • • • • • • • • / • LU • • • ^ • • • • * h- • (/) 4 — LU / • -* • 1 ,1,1 » 1 . 1 . 1 . 100E 120E 140E 160E 180 160W 140W 120W 10 LONGITUDE 26 fisheries between neighbouring regions as previous researchers (Fujino 1970, 1976; Sharp 1978), using different sets of blood genetics data, have suggested. However, the blood genetics data support the conclusion that interaction between fisheries at the longitudinal extremes of the study area is minimal, and that the degree of interaction should increase as the distance between fisheries decreases (see Section 4,6). « 4.4.2 Parasite results During the second survey in Tonga, skipjack body cavities, viscera and gills were examined for the presence of parasites which could possibly be used in stock structure studies. These samples have been compared with samples collected over a wide range of tropical waters. Preliminary results presented by Lester (1981) showed that the parasite fauna of skipjack from tropical waters, over widely separated areas, is quite similar, and that skipjack caught in New Zealand carried many tropical parasites. Analyses of these data are continuing; however, the preliminary results are not promising for clarifying regional fishery interactions in tropical waters using parasite fauna, nor is it likely that definition of skipjack population structure by further analysis of the existing parasite data will be greatly improved. 4.5 Skipjack Migration Figure B (inside back cover) is a straight line migration map summarising Skipjack Programme tag returns for the entire survey area. Only a subset of all tag returns is illustrated (one arrow in each * direction between each pair of 10 degree squares). Table 13 is a matrix which shows the number of fish tagged in each country and recaptured in other countries, or in the country of release. A feature of the overall migration data is that there appear to be no oceanic barriers to the movement of skipjack in the study area, but this was not the case for all tagged skipjack that were returned to the Programme. Figure 6 shows that most recoveries occurred within one month of tagging and close to the point of release, however there was a tendency for at least a portion of the tagged population to migrate. Figure 7 shows straight line migrations for six of the seven tagged skipjack known to have made international migrations into or out of the waters of Tonga. Appendix C lists tagging and recovery data for these recaptures. Fish moved into Tonga from both temperate and tropical waters and all migrations by tagged skipjack into or out of Tonga showed a net movement to the east. The 200-mile exclusive economic zone of Tonga is bordered by Niue, Fiji, Wallis and Futuna, Western Samoa, and American Samoa. The Skipjack Programme tagged a total of 40,920 skipjack in these six areas; 2,139 skipjack were subsequently recaptured (to October 1982). An examination of these tagging data can be informative of skipjack movements in Tonga. Release and recapture information is listed in Appendix D, and a selection of these tag migrations is shown in Figure 8. Information from these returns show that there is at least some movement of tagged skipjack from this area into areas as far east as the Society Islands, as far west as Papua New Guinea, as far north as Wake Island, and as far south as New Zealand. TABLE 13. SKIPJACK TAG RELEASE/TAG RECOVERY MATRIX FOR ALL TAG RELEASES RECOVERIES RECEIVED BY THE PROGRAMME AS OF 16 DECEMBER 1982. Releas are arrayed by tagging or recovery location, usually a country or te cases where small geographical divisions were more informative; ab explained in Appendix E. Not included in the table are returns for or area was unknown. COUNTRY OF RECAPTURE AMS CAL FIJ GIL GUM HAW HOW INO INT JAP KOS LIN HAQ MAR MAS MTS NAU NCK NOR NSW PAL PAM PHL PHO PNG PON OLD SOC SOL TO 775 AMS 3 10219 CAL 18 1 2 1 20094 FIJ 1 1949 1 5 1 4 >- 174 GAM en 4569 GIL 1 385 32 1 1 14 1 2 1 1- 108 JAP 1 3 7 11 Z 297 KOS 3 2 D 20282 MAO 1 4 42 1 195 MAR 2 1 2 1 o 327 MAS 2 1 1 o 1229 NCK >- 91 NIU m 1113 NOR 2 1 1 U) 4322 NSW 1 6 2 1 2 1 8 Ul 7233 PAL 3 28 67 3 104 5 77 7 2 U) 367 PHO 1 < 59 PIT 8550 PNG 1 5 7 18 1 7 2 2 958 3 1 26 5518 PON 1 2 17 2 23 1 29 1 1 58 1 EL E Od 2651 OLD 3 2 25 48 SCK u. 1725 SOC O 6221 SOL 1 1 64 TOK 1969 TON 1 1 1054 TRK 4 5 5 19 S528 TUA 5 2904 TUV 2 2 17 1 4 1 1 1 1 2 1254 VAN 1 4 NUMBE R 16065 WAL 1 14 S 5 10 3 24 2 3 1926 WES 1 1 1 778 YAP 2 3 7 1 3 1 1 12734 ZEA 5 31 3 1 2 5 140443 TOT l5 36 2000 405 38 41 189 11 34 1 42 9 72 1 4 1 1 4 107 5 6 32 1057 92 3 54 605 28 FIGURE 6. NUMBERS OF SKIPJACK TAG RECOVERIES BY DISTANCE TRAVELLED AND TIME-AT-LARGE FOR THE TOTAL SKIPJACK PROGRAMME DATA SET. Data are for tag returns received by 4 November 1982. Recaptures for 96 fish which travelled more than 1,500 nautical miles are included in the sample sizes, but not shown in the figure. 2500 <30 DAYS AT LARGE 2000 N=2776 1500 1000 500 Q i. il i UJ 0 250 500 750 1000 1250 1500 CC => I- Q- < 800 O UJ 31-180 DAYS AT LARGE N=1428 o*: < Q_ if) O en Ul GO 0 250 500 750 1000 1250 1500 2 150i >180 DAYS AT LARGE N=1039 250 500 750 1000 1250 1500 DISTANCE TRAVELLED (NAUTICAL MILES) FIGURE 7, STRAIGHT LINE MIGRATION ARROWS FOR TAGGED SKIPJACK RELEASED IN TONGA AND OTHER AREAS, AND FOR TAGGED SKIPJACK RELEASED IN OTHER AREAS AND RECAPTU Six tag migrations are plotted. Tick marks on the arrows indicate in days. 1 TOE 120E 130E 140E 150E 160E 170E 180 MOW 160W 150W 10E 120E 130E T40E 150E 160E Z^70E 180 1-QYJ 160W 150W FIGURE 8. MIGRATION ARROWS FOR 80 OF 2,139 RECOVERIES OF SKIPJACK TAGGED IN THE WAT FIJI, WALLIS AND FUTUNA, WESTERN SAMOA, AMERICAN SAMOA, AND NIUE. Tag m been selected to show no more than two examples between any pair of squares. Each tick mark on the arrows represents 30 days at large. 1 10E 120E 130E 140E 150E 160E 170E 180 170W 160W 150W 110E 120E 130E 140E 1 50E 1 60E 1 JOE 180 1-70W 160W 150W 31 The limited fishing activity in the waters of Tonga and the lack of data for fisheries in the zones surrounding Tonga contribute to the difficulty of studying skipjack movements and thus determining migratory patterns in this area. The lack of recent (1979 to 1982) catch information for the Japanese long-range pole-and-line fleet is particularly limiting. The pattern of tag recoveries in Figure 8 shows that most skipjack were recovered to the north and northwest, a reflection, in part, of large fisheries in this direction. Little fishing takes place to the east and southeast, so the five recoveries in French Polynesia, from a very small fishery (Gillett and Kearney 1983), may indicate movement of a sizeable group of skipjack, but this cannot be confirmed without complete catch and effort statistics. 4.6 Fishery Interactions The tag recapture data indicate that skipjack may undertake long migrations in most directions in the western Pacific, including to and from Tonga. Results from electrophoretic analysis of skipjack blood samples suggest that in the study area there are no genetically isolated skipjack subpopulations separated by stable geographical barriers. Therefore, there is potential for at least some interaction between the fishery in Tonga and fisheries in other countries. Using the available catch statistics and tag recoveries, several measures of fishery interactions are possible: the change in catch in one fishery resulting from increased catches in other fisheries, within a generation or between generations; the fraction of recruitment (or standing stock) that arises from immigration from neighbouring fished areas; the change in yield per recruit resulting from different fishing strategies. The absence of any demonstrable relationship between catch per unit effort and effort for all the world's skipjack fisheries suggested that between-generation fishery interactions would be negligible for present or even greatly expanded fisheries in the western and central Pacific. Therefore evaluation of interactions within one generation was considered more urgent. The initial approach followed by the Skipjack Programme was to use tagging data as well as catch statistics to estimate coefficients of migration between particular fisheries (Skipjack Programme 1981a). The product of the estimated population size in the donor fishery and the migration coefficient gave an estimate of the tonnes of skipjack migrating between fishing areas. Comparison of these migration estimates with estimates of population size in the destination country, or in the donor country, illustrated stock interactions within one skipjack generation, since they measured the fraction of the standing stock that migrated to or from a particular area. Results demonstrated a generally low level of stock interaction for existing locally based fisheries. A more appropriate expression of interaction is the percentage of recruitment (throughput) in the destination country that is due to immigration from the donor country (Tuna Programme, manuscript in preparation). This estimate of interaction is independent of the correction factor applied to account for non-return of recaptured tags, return of tags with insufficient or inaccurate recapture data, and loss of tags immediately after application through slippage or mortality, assuming that the correction factor is the same in the donor and destination countries. There are four pairs of countries and territories in the Skipjack Programme study area for which estimates of interaction due to 32 skipjack movement have been completed (Table 14). These are Papua New Guinea - Solomon Islands, New Zealand - Fiji, New Zealand - Society Islands, and New Zealand - Western Samoa. As shown in column four of the table, skipjack immigrants from the fished area in a particular donor country were generally a small fraction (<10%) of recruitment (throughput) in the destination country's fished area, which implies that interactions amongst fisheries in these countries are generally minor. It should be noted that this situation applies only to skipjack of the size tagged by the Programme (most were between 40 and 60 cm). Skipjack smaller than this range could very well move large distances and contribute significantly to interactions between stocks in the fished areas. However, as fisheries of the SPC region are not yet exploiting fish less than 40 cm to any great degree, it can be reasonably assumed that fishery-induced interactions resulting from movement of small fish are presently negligible. TABLE 14. SUMMARY OF FISHERY INTERACTIONS BETWEEN LOCAL FISHERIES Range of Estimates of Percentage of Average Annual Destination Country Destination Throughput from Country Catch Donor Country Donor Country Destination Country in Tonnes (years) Migrants Solomon Islands Papua New Guinea 38400 (1978,1979) 1% to 5% Papua New Guinea Solomon Islands 22100 (1979-1981) 2% New Zealand Fiji 3800 (1979-1981) 8% to 12% New Zealand Western Samoa 700 (1976-1978) 14% New Zealand French Polynesia 1500 (1978-1980) 9% (Society Islands) Fiji New Zealand 8800 (1980-1981) <1% It has been pointed out that fishery interactions increase as the distance between fisheries decreases. Thus, if fisheries in neighbouring countries were to expand their areas of operation to include more of the waters adjacent to their common borderlines, the degree of interaction could be expected to increase. Furthermore, if substantial fisheries were to develop in overlapping areas, such as purse-seine and pole-and-line fleets operating in the same waters within a country, then the degree of interaction would be much higher than that among locally based fisheries which at present are all relatively isolated. Interactions affecting the skipjack resource in the waters in Tonga can be expected to increase as fisheries in the waters of countries and territories surrounding Tonga expand. 4.7 Skipjack Population Dynamics One of the main reasons for tagging skipjack was to estimate various population parameters which indicate the magnitude of the skipjack resource and its resilience to fishing pressure. The parameters considered here are: (1) the population, which is the standing stock of fish which are available to the fishery; (2) the attrition rate, which under steady state 33 conditions is the population turnover rate, or the proportion of the population cycling through the area in a period of time due to immigration, emigration, local productivity and mortality; (3) the throughput, which is the product of the population size and the attrition rate, and which may be defined as the tonnes of fish cycling through the area per unit time; and (4) the harvest ratio, which is the ratio of monthly catch to throughput. Of the four parameters, throughput is the best measure of the magnitude of the skipjack resource because it is a rate against which catch (also a rate) can best be compared. A high throughput relative to catch is evidence (though not proof) that fishing is having little impact on the fish stocks. The population size alone gives little indication of the harvest rate that the population can support without becoming depleted. In order to obtain parameter estimates and confidence ranges for these estimates, a tag recapture and attrition model was fitted by an iterative regression technique (Conway, Glass and Wilcox 1970) to the tag recovery data (Figure 9) for the total study area (Kleiber, Argue and Kearney 1983). The best fitting values for the parameters and their 95 per cent confidence limits are given in Table 15. These values have been adjusted using the correction factor described in Section 4.6. TABLE 15. SKIPJACK POPULATION PARAMETERS AND 95 PER CENT CONFIDENCE LIMITS ESTIMATED FROM AGGREGATE TAG RETURNS. The aggregate data set includes skipjack returns from all releases by the Skipjack Programme. Estimates of population size, throughput and fishing mortality have been corrected for recaptured tags that were not returned or were returned with insufficient data, for mortality due to tagging, and for tag shedding. Results from Kleiber, Argue and Kearney (1983). Confidence Estimate Limits Attrition (turnover) per mon th 0.17 (0.15 - 0.20) Population size (tonnes) 3,000,000 (2,500,000 - 3,700,000) Throughput per month 520,000 (460,000 - 590,000) Catch per month 19,000 Fishing mortality per month 0.0063 (0.0051 - 0.0077) Harvest ratio (unitless) 0.037 (0.032 - 0.042) The average catch for the whole of the study area during the years that the tagged fish were at large, approximately 19,000 tonnes per month, is very low compared to the throughput of 520,000 tonnes per month (harvest ratio of 0.037), implying that current harvest levels are not reducing skipjack stocks. The parameter estimates in Table 15 were derived from the aggregate tag recovery data. As such they represent average values for a large region and the values for particular countries vary considerably. The model was applied to tag return data from releases in the waters of individual countries. To do so, it was necessary to have a considerable number of tagged fish recovered in the area over an extended period of time, and a record of the fishing effort and/or catch. The lack of these data for Tonga meant that it was not possible to estimate skipjack FIGURE 9. NUMBER OF SKIPJACK TAG RECOVERIES VERSUS MONTHS AT LARGE. The Y-axis i 1000: I H Z o 100: DC UJ Q_ U) z D xl 0 20 MONTHS AT LARGE 35 population parameters in this area, although it is obvious that the annual skipjack catch in Tonga of a few hundred tonnes is having a negligible impact on the skipjack resource in Tonga or elsewhere. Areas such as Fiji, Solomon Islands and Papua New Guinea where larger local fisheries exist and where it was possible to make population parameter estimates, appear to have considerable potential for expansion of their fisheries (Kearney 1982a; Argue and Kearney 1982; Tuna Programme MS). 4.8 Yellowfin Although the Skipjack Programme concentrated on studies of skipjack, other tuna species, primarily yellowfin, were studied on an opportunistic basis. These investigations included tagging, examination of stomach contents, inspection of gonads to determine sex and maturity, and size measurements. Further studies on yellowfin form an important part of the SPC Tuna and Billfish Assessment Programme. Yellowfin tuna accounted for 12 per cent of the total tuna catch (by weight) taken by the Skipjack Programme in the waters of Tonga (Table 1), and 20 per cent of the schools sighted in Tonga were known to have contained at least some yellowfin tuna (Table 1). Table 8 lists the number of yellowfin tuna that were examined for biological data in Tonga and Figure 10 presents their size frequency distribution. Two hundred and sixty-two yellowfin were tagged in the waters of Tonga during the two visits. One tagged yellowfin was recaptured in Fiji 102 days after release in Tonga, and another was recaptured by a Korean longliner, but complete recapture details are not known for this fish (Appendix C). FIGURE 10. LENGTH FREQUENCY DISTRIBUTION FOR YELLOWFIN SAMPLED IN THE WATERS OF TONGA. N is the sample size. 20 z 15 o N 94 Ld >- U_ 10 o Hit a: UJ m 5- '•?-m Z £ m2 i n n H p 35 45 55 65 75 85 95 105 FORK LENGTH (cm) FIGURE 11. STRAIGHT LINE REPRESENTATION OF MOVEMENTS OF YELLOWFIN TAGGED BY THE SK AND SUBSEQUENTLY RECOVERED. Recoveries have been selected to show n example of movement in each direction between any pair of two degree marks denote intervals of 30 days between release and recapture dates. 110E 120E 130E 140E 150E 160E 170E 180 170W 160W 150W 140W 130W , , , , , , 1 r —, , V*^-. HOE 120E 130E 140E 150E 160E 170E 180 170W 160W 150W 140W 130W 37 A total of 9,596 yellowfin were tagged in all of the countries in the study area. Of these, 210 (2.2 per cent) were recaptured and returned by October 1982. Figure 11 is a straight line migration map showing the movement of these tagged yellowfin. Table 16 shows that average daily rates of movement for skipjack and yellowfin are nearly identical. The average distance between release and recapture is, however, greater for yellowfin due to their longer time at liberty. TABLE 16. COMPARISON OF SKIPJACK AND YELLOWFIN MOVEMENT Number of Tag Average Time Average Distance Average Rate Returns at Liberty Travelled of Movement (days) (nautical miles) (miles/day) Skipjack 5,581 94 175 1.86 Yellowfin 209 131 246 1.88 5.0 CONCLUSIONS It is appreciated that there are limitations to resource assessments which are based largely on data from two short visits to a country. However, the data generated by the Skipjack Programme throughout the central and western Pacific are relevant to the overall evaluation of the skipjack resource in Tonga. Therefore, these data, in combination with other documents referenced, provide assessments which were not previously possible and which are submitted as being the best available. Examination of Skipjack Programme baitfishing results and catch records from other surveys indicate that the baitfish potential in Tonga is highest in the Vava'u area, although it is not great overall. Based on estimates of potential baitfish catch for Vava'u (Thomas 1978), which we consider to be optimistic, and estimates of baitfish effectiveness (Section 4.1.2), the estimated tuna catch in the Vava'u area using local live-bait resources would be less than 300 tonnes per season. Fluctuations in baitfish supply are almost certain to occur and would probably have a negative impact on tuna landings. Large-scale development predicated on a baitfish catch which could be used to capture only 300 tonnes of tuna is clearly not practical. Thus, pole-and-line fishing effort more ambitious than the present two vessels does not seem warranted. The Skipjack Programme had average tuna fishing success for skipjack and yellowfin in Tonga. The abundance of surface schools of these species was likewise considered average; however, the reported strong seasonality in their abundance is a drawback for year-round fishing. Little information is available to indicate the possible success of purse-seining in Tonga. Efforts to obtain this information should be encouraged since such information will undoubtedly affect decisions relating to the direction of fisheries development in Tonga. If seining does prove feasible here, Tonga has the advantage of being relatively close to the major canning and port facilities in American Samoa. Analyses of skipjack blood genetics and tagging data imply that 38 skipjack present in Tonga are not part of any geographically isolated subpopulation. The overall migration study revealed that skipjack are truly a regional resource. Tagging data from Tonga and adjacent areas show that interaction with fisheries at a considerable distance does occur, but the magnitude of interaction is probably quite small at present. Available information indicates that catches from Tonga are having a negligible impact on the skipjack population, and there appears to be no biological reason why the yield from the skipjack resource could not be substantially increased, perhaps to the level of 10,000 tonnes that was proposed by Ratcliffe et al. (1981). 39 REFERENCES ALEXANDER, A.B. (1902). Notes on the boats, apparatus and fishing methods employed by the natives of the South Sea Islands, and results of fishing trials by the Albatross. United States Commissioner of Fish and Fisheries Report for 1901. 27:743-829. ANON (1969). Report of the UNDP/FAO Tuna Mission to the South Pacific, May-June 1969. [FAO, Rome, Italy] 11 pp. + 6 Annexes. Mimeo. ANON (1973). Report of the activities of the skipjack survey in the waters of the South Pacific Ocean. Japan Marine Fishery Resource Research Center, Tokyo, Japan. Translated by Hokoku Marine Products Limited, May 1981. 18 pp. ANON (1974). 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Comparative Biochemistry and Physiology 31:249. SHARP, G.D. (1978). Behavioural and physiological properties of tunas and their effects on vulnerability to fishing gear. Tn Sharp, G.D. and A.E. Dizon (Eds). The physiological ecology of tunas. Academic Press, New York. pp. 397-450. SIBERT, J.R., R.E. KEARNEY and T.A. LAWSON (1983). Variation in growth increments of tagged skipjack (Katsuwonus pelamis). Tuna and Billfish Assessment Programme Technical Report No.10, South Pacific Commission, Noumea, New Caledonia. SIMIKI, T., C. RATCLIFFE and W. SORRENSON (1981). Report on the deep sea 43 tuna fishing industries in American Samoa and the Solomon Islands. Fisheries Working Paper No.1, Fisheries Division, Ministry of Agriculture, Forestry and Fisheries, and the Central Planning Department, Nuku'alofa, Tonga. 45 pp. SKIPJACK PROGRAMME (1980). Skipjack fishing effort and catch, 1972-1978, by the Japanese pole-and-line fleet within 200 miles of the countries in the area of the South Pacific Commission. Skip jack Survey and Assessment Programme Technical Report No.2, South Pacific Commission, Noumea, New Caledonia. 91 pp. SKIPJACK PROGRAMME (1981a). Skipjack migration, mortality and fishery interactions. Regional Technical Meeting on Fisheries 1981 . 13 : Working Paper No.9, South Pacific Commission, Noumea, New Caledonia. 35 pp. SKIPJACK PROGRAMME (1981b). An appraisal of genetic analysis of skipjack blood samples. Regional Technical Meeting on Fisheries 1981 . 13 : Working Paper No.10, South Pacific Commission, Noumea, New Caledonia. 8 pp. SKIPJACK PROGRAMME (1981c). An overview of results from analysis of data on growth of skipjack. Regional Technical Meeting on Fisheries 1981, 13 : Working Paper No.11, South Pacific Commission, Noumea, New Caledonia. 11 pp. SKIPJACK PROGRAMME (1981d). An assessment of baitfish resources in the South Pacific Commission area. Regional Technical Meeting on Fisheries 1981, 13 : Working Paper No.12, South Pacific Commission, Noumea, New Caledonia. 8 pp. SKIPJACK PROGRAMME (1981e). Further observations on fishing performance of baitfish species in the South Pacific Commission area. Regional Technical Meeting on Fisheries 1981. 13 : Working Paper No.13, South Pacific Commission, Noumea, New Caledonia. 15 pp. SKIPJACK PROGRAMME (1981f). Fishing effort and catch by the longline fleets of Japan (1962-77) and Taiwan (1967-77) within 200 miles of the countries in the area of the South Pacific Commission. Skip i ack Survey and Assessment Programme Technical Report No.3, South Pacific Commission, Noumea, New Caledonia. 249 pp. THOMAS, D. (1978). Tonga marine resource development : A report prepared for the Fisheries Investigation Project (1975-1977). FAO/FI:TON/74/004/l. Food and Agriculture Organization of the United Nations, Rome. 102 pp. TUNA PROGRAMME (Manuscript). An assessment of the skipjack and baitfish resources of Papua New Guinea. Skipjack Survey and Asses sment Programme Final Country Report. South Pacific Commission, Noumea, New Caledonia. VAEA, H. and W. STRAATMANS (1954). Preliminary report on a fisheries survey in Tonga. Journa1 of the Polynes ian Society 63(3 and 4):199-215. VAN PEL H. (1956). Fisheries in Tonga. South Pacific Commission, Noumea, New Caledonia. 5 pp. 44 WILKINSON, W.A. (1974). Fisheries development in Tonga. Regional Technical Meeting on Fisheries 1974, 7 : Working Paper No. 2 , Nuku'alofa, Tonga. 8 pp. WILLIAMS, L. (1969). A brief resume of fishery development in Tonga. Tonga Department of Agriculture, Nuku'alofa, Tonga. 6 pp. 45 APPENDIX A. SCIENTISTS, OBSERVERS AND CREW ON BOARD THE RESEARCH VESSELS South Pacific Commission Scientists Robert Gillett 11 April - 3 May 1978 Desmond Whyman 11 April - 3 May 1978 Christopher Thomas 11 April - 3 May 1978 Jean-Pierre Hallier 3-9 March 1980 A.W. Argue 3-9 March 1980 James lane Hi 3-9 March 1980 Representatives of the Department of Agriculture. Tonga Tevita Fusimalohi 12-14 April 1978 Peter Gibson 16, 18-19, 25-26 April 1978 Siaosi Fuka 14-18 April 1978 Nobuyuki Irokawa 16, 26-27 April 1978 Ioane Fakahau 16-17, 23-24 April 1978 Sione Kolo 17-18, 28-30 April 1978 Observers Anthony Hopson 5-6 March 1980 Fisheries Division, Tonga P. Finau 7 March 1980 Fisheries Division, Tonga Archie Moana 3-6 March 1980 Fisheries Officer, Niue Samisoni Kata 3-6 March 1980 Fisherman, Niue Savali Time 3-5 March 1980 Fisheries Officer Western Samoa Dan Popper 3-5 March 1980 Food and Agriculture Organi zation Japanese Crew Japanese Crew Cruise One Cruise Two Masahiro Matsumoto, Captain Mitsutoyo Kaneda, Captain Yoshio Kozuka Tsunetaka Ono Yoshikatsu Oikawa Mikio Yamashita Ryoichi Eda Yoshikatzu Oikawa Sakae Hyuga Seima Kobayashi Mikio Yamashita Kenji Arima Yoshihiro Kondoh Yukio Sasaya Akio Okumura Kohji Wakasaki Kohji Wakasaki Yoshihiro Kondoh 46 Fiiian Crew Fijian Crew Cruise One Cruise Two Eroni Marawa Ravaele Tikovakaca Vonitiese Bainimoli Kitione Naivaurerega Ravaele Tikovakaca Samuela Ue Vonitiese Bainimoli Lui Andrews Mosese Cakau Samuela Delana Samuela Ue Jona Ravasakula Lui Andrews Josua Raguru Kitione Koroi Eroni Dolodai Jone Manuku Metuisela Koroi Jona Ravasakula Luke Kaidrokai Lui Diva Aminiasi Kuruyawa Samuela Delana Napolioni Ravitu Taniela Verekila 47 APPENDIX B. BAIT SPECIES, PERCENTAGE OF BOUKI-AMI HAULS CONTAINING A PARTICULAR SPECIES, AND ESTIMATED TOTAL CATCH, FOR THE SKIPJACK PROGRAMME SURVEY IN THE WATERS OF TONGA Percentage Estimated Species Occurrence Catch (kg) Stolephorus devisi 34 231 Pranesus pinguis 82 229 Spratelloides delicatulus 75 151 Selar crumenophthalmus 70 128 Atule mate 27 123 Hvpoatherina ovalaua 75 108 Sardinella sirm 25 82 Herklotsichthvs punctatus 50 72 Spratelloides gracilis 34 23 Scomberoides sp. 14 4 Gazza minuta 5 4 Stolephorus indicus (i) 2 1 Sardinella sp. 2 0 Leioenathus bindus 5 0 Sp. of Apogonidae 7 0 Megalaspis cordvla 5 0 Sp. of Lutjanidae 5 0 Caranx sp. 25 0 Decapterus macrosoma 25 0 Sp. of Acanthuridae 5 0 Archamia lineolata 9 0 Dussumieria sp. 9 0 Sp. of Sphyraenidae 20 0 Sp. of Priacanthidae 9 0 Mullodichthvs sp. 5 0 Thrissina baelama 5 0 Rastrellieer kanaeurta 2 0 Dactvloptera orientalis 25 0 Sp. of Mullidae 14 0 Breemaceros sp. 2 0 Sp. of Holocentridae 7 0 Stolephorus indicus 7 0 Sp. of Ostraciidae 9 0 Sp. of Hemirhamphidae 9 0 Sp. of Eleotridae 2 0 Priacanthus sp. 2 0 Sp. of Anguillidae (j) 2 0 Zanclus canescens 2 0 Apoeon(Rhabdamia) cvpselurus 5 0 Rastrellieer sp. 5 0 Sp. of Squid 2 0 Sardinella melanura 7 0 Sp. of Atherinidae 5 0 Mullodichthvs samoensis 11 0 Fistularia sp. 20 0 Sp. of Chaetodontidae 18 0 Apogon(Rhabdamia) gracilis 5 0 Stolephorus sp. (i) 9 0 Sp. of Bothidae 14 0 Sp. of Mugilidae 18 0 Sp. of Tetrodontidae 18 0 Sp. of Balistidae 20 0 Sp. of Carangidae 2 0 Sp. of Synodontidae 5 0 Cheilodipterus macrodon 7 0 * Several recent revisions of scientific names used in a previous Skipjack Programme report on Tonga have been maintained. The most notable changes in nomenclature have been : Herklotsichthvs punctatus to Herklotsichthvs quadrimaculatus Pranesus pinguis to Ather Lnomorus lacunosa. 49 APPENDIX C. DETAILS OF TAGGED FISH KNOWN TO HAVE MADE INTERNATIONAL MIGRATIONS INTO OR OUT OF TONGA Date Latitude Longitude Size Country Skipjack SC03859 release data: 78/02/09 18deg 53'S 179deg 16'E 48.0cm FIJI recapture data: 79/05/10 18deg 38'S 174deg 04'W . cm TON At large for 455 days Distance = 379.0 naut. miles in direction 89.deg. true, SC04101 release data: 78/02/09 18deg 51'S 179deg 12'E 53.0cm FIJI recapture data: 78/07/22 21deg 08'S 175deg 12'W . cm TON At large for 163 days. Distance = 344.2 naut. miles in direction 114.deg. true. SE00152 release data: 78/04/17 18deg 39'S 174deg 12'W 54.0cm T0N1 recapture data: 79/04/17 17deg 47'S 148deg 36'W 65.0cm SOC At large for 365 days, Distance = 1458.7 naut. miles in direction 92.deg. true, SE00366 release data: 78/04/25 18deg 20'S 174deg 16'W 48.0cm T0N1 recapture data: 78/06/14 14deg 05'S 171deg 50'W 51.0cm WES At large for 50 days, Distance = 291.0 naut. miles in direction 29.deg. true. SE00838 release data: 78/04/27 18deg 39'S 174deg 08'W 50.0cm T0N1 recapture data: / / deg deg ' 52.5clm SE01182 release data: 78/04/30 20deg 53'S 175deg 15'W 51.7cm T0N1 recapture data: 78/10/08 03deg 46'S 173deg 17'W . cm PHO At large for 161 days. Distance = 1033.4 naut. miles in direction 7.deg. true. SK02519 release data: 79/03/02 35deg 24'S 174deg 54'E 47.0cm ZEA1 recapture data: 80/02/20 21deg 04'S 175deg 22'W 52.5cm TON At large for 355 days. Distance = 1000.8 naut. miles in direction 33.deg. true. Yellowfin SE00625 release data: 78/04/19 18deg 29'S 174deg 07'W 51.0cm TON1 Y recapture data: 78/07/30 17deg 15'S 179deg 10'E 58.5cm FIJ At large for 102 days. Distance = 390.6 naut. miles in direction 280.deg. true. SE01101 release data: 78/04/30 20deg 44'S 175deg ll'W 51.0cm T0N1 recapture data: 79/06/03 06deg 50'S HOdeg 46'W 91.6cm to to to 80/03/05 30deg 33'S 174deg 52'W 51 APPENDIX D. RESULTS OF SKIPJACK TAGGING IN TONGA AND THE SURROUNDING AREAS OF FIJI, WALLIS AND FUTUNA, WESTERN SAMOA, AMERICAN SAMOA, AND NIUE (AS OF OCTOBER 1982) Release Month/ No. Released Recapture Month/ No. Recaptured Area Year Area Year AMS 06/78 74 AMS 02/80 701 AMS 02/80 WES 04/80 FIJ 01/78 876 FIJ 01/78 FIJ 02/78 FIJ 03/78 FIJ 04/78 FIJ 05/78 FIJ 06/78 FIJ 07/78 FIJ 02/79 FIJ unknown FIJ 02/78 3,539 FIJ 02/78 306 FIJ 03/78 82 FIJ 04/78 9 FIJ 05/78 6 FIJ 06/78 3 FIJ 07/78 3 FIJ 05/80 2 FIJ unknown 22 TON 07/78 TUV 07/78 TUV 02/79 WAR 10/79 ZEA 03/79 FIJ 03/78 2 FIJ 04/78 4,031 FIJ 04/78 284 FIJ 05/78 6 FIJ 06/78 3 FIJ 07/78 3 FIJ 02/79 2 FIJ 06/79 FIJ 03/81 FIJ unknown INT 09/78 INT 02/80 NAU 04/79 PHO 09/78 SOC 01/79 WAL 05/80 WES 08/78 WES 02/79 ZEA 11/78 ZEA 01/79 FIJ 04/80 11,646 CAL 11/80 FIJ 04/80 670 FIJ 05/80 18 FIJ 06/80 FIJ 07/80 1 FIJ 08/80 19 FIJ 09/80 2 FIJ 10/80 2 FIJ 11/80 2 FIJ 12/80 11 FIJ 01/81 27 FIJ 02/81 42 FIJ 03/81 35 FIJ 04/81 8 FIJ 05/81 12 FIJ 06/81 10 FIJ 07/81 5 FIJ 08/81 1 FIJ 10/81 3 FIJ 11/81 1 FIJ 12/81 1 FIJ unknown 23 52 NIU 02/80 91 TON 04/78 1,402 PHO 10/78 SOC 04/79 TON 05/78 WES 06/78 unknown unknown TON 03/80 567 TON 04/80 WAL 05/78 13,513 CAL 12/79 FIJ 07/78 FIJ 01/79 FIJ 02/79 FIJ 03/79 FIJ 07/79 FIJ 07/80 FIJ unknown HOW 08/79 HOW 04/80 HOW 06/80 HOW 07/80 INT 10/78 INT 11/78 INT 10/79 INT 04/80 INT 08/80 INT 02/81 KIR 09/78 KIR 10/78 KIR 02/79 KIR 01/80 MAS 09/78 MAS 11/79 MAS 02/80 PHO 08/78 PHO 09/78 PHO 10/78 15 PHO 11/78 PHO 09/80 PNG 09/79 PNG unknown SOC 02/79 SOC 07/79 SOC 08/79 TRK 03/79 TUV 01/79 WAL 05/78 49 WES 07/78 WES 08/78 WES 10/78 ZEA 01/79 ZEA 03/79 ZEA 04/79 WAL 05/80 2,552 FIJ 02/81 FIJ 03/81 INT 10/80 INT 02/81 MAS 02/81 PHO 09/80 PHO 03/81 WAL 05/80 WES 12/80 WES 06/78 1,767 AMS 01/79 SOL 05/80 WES 06/78 WES 07/78 WES 10/78 WES 11/78 WES 05/79 ZEA unknown WES 02/80 159 SOC 12/80 WES 02/80 WES 04/80 WES 05/80 TOTAL 40,920 2,139 53 APPENDIX E. ABBREVIATIONS FOR COUNTRIES, TERRITORIES AND SUBDIVISIONS THEREOF AMS - American Samoa CAL - New Caledonia COK - Cook Islands FIJ - Fiji GAM - Gambier Islands (French Polynesia) GIL - Gilbert Islands (Kiribati) GUM - Guam HAW - Hawaii HOW - Howland and Baker Islands (U.S. Territory) IND - Indonesia INT - International waters JAP - Japan JAR - Jarvis (U.S. Territory) KIR - Kiribati KOS - Kosrae (Federated States of Micronesia) LIN - Line Islands (Kiribati) MAQ - Marquesas Islands (French Polynesia) MAR - Northern Mariana Islands MAS - Marshall Islands MTS - Minami-tori shima (Japan) NAU - Nauru NCK - Northern Cook Islands NIU - Niue NOR - Norfolk Island NSW - New South Wales (Australia) PAL - Palau PAM - Palmyra (U.S. Territory) PHL - Philippines PHO - Phoenix Islands (Kiribati) PIT - Pitcairn Islands PNG - Papua New Guinea POL - French Polynesia PON - Ponape (Federated States of Micronesia) QLD - Queensland (Australia) SCK - Southern Cook Islands SOC - Society Islands (French Polynesia) SOL - Solomon Islands TOK - Tokelau TON - Tonga TRK - Truk (Federated States of Micronesia) TUA - Tuamotu Islands (French Polynesia) TUV - Tuvalu VAN - Vanuatu WAK - Wake Island (U.S. Territory) WAL - Wallis and Futuna WES - Western Samoa YAP - Yap (Federated States of Micronesia) ZEA - New Zealand