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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.

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