An Assessment of the Skipjack and Baitfish Resources of Solomon Islands
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AN ASSESSMENT OF THE SKIPJACK AND BAITFISH RESOURCES OF SOLOMON ISLANDS A.W. Argue and R.E. Kearney Skipjack Survey and Assessment Programme Final Country Report No. 3 South Pacific Commission Noumea, New Caledonia November 1982 ^fv^ Hf*. AN ASSESSMENT OF THE SKIPJACK AND BAITFISH RESOURCES OF SOLOMON ISLANDS A.W. Argue and R.E. Kearney Skipjack Survey and Assessment Programme Final Country Report No.3 South Pacific Commission Noumea, New Caledonia November 1982 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. The Skipjack Programme has been succeeded by the Tuna and Billfish 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 is continuing under the Tuna Programme. Papers referred to as manuscripts in this final country report will be released over the duration of the Tuna Programme. 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. Farman, R.D. Gillett, P.M. Kleiber, 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 the people of Solomon Islands, particularly the officials of the Fisheries Division in the Ministry of Natural Resources, for making its stay more productive and enjoyable. For supplying catch statistics, sampling statistics and tag returns from the Solomon Islands fishery, the authors wish to thank Doug Gibson, Chief Fisheries Officer, David Evans, Fishery Biologist, and Christine Mansfield, Biometrician, of the Solomon Islands Ministry of Natural Resources, Honiara. Tuna Programme South Pacific Commission V CONTENTS Page PREFACE iii LIST OF TABLES vii LIST OF FIGURES ix 1.0 INTRODUCTION 1 1.1 Background to the Tuna Fishery 1 2.0 SKIPJACK PROGRAMME RESEARCH PLAN 6 3.0 VESSEL AND CREW 6 4.0 METHODS 6 4.1 Skipjack Fishing, Tagging and Biological 7 Sampling 4.2 Baitfishing 8 4.3 Data Compilation and Processing 8 4.4 Data Analysis 8 5.0 SUMMARY OF FIELD ACTIVITIES 8' 6.0 RESULTS AND DISCUSSION 12 6.1 Baitfishing 12 6.1.1 General observations 12 6.1.2 The Slot and vicinity 19 6.1.3 Other baiting localities 22 6.2 Tuna Fishing Results 23 6.2.1 General observations 23 6.2.2 Ontong Java 25 6.2.3 Santa Cruz Islands 26 6.3 Skipjack Population Biology 27 6.3.1 Maturity and juvenile recruitment 27 6.3.2 Skipjack diet 28 6.3.3 Skipjack growth 29 6.3.4 Population structure 30 6.4 Skipjack Tagging Results 32 6.4.1 Solomon Islands tagging 32 6.4.2 International migrations from 35 Solomon Islands 6.4.3 International migrations to 37 Solomon Islands 6.4.4 Mortality, production and fishery 42 interactions 6.5 Yellowfin Biology and Tagging Results 50 7.0 CONCLUSIONS 52 7.1 Baitfish 52 7.2 Skipjack 53 REFERENCES 55 VI APPENDICES A. Scientists, observers and crew on board the research 61 vessels B. Bait species composition, percentage of bouki-ami hauls containing a particular species, and estimated total 63 catch, for the 1977 and 1980 Skipjack Programme surveys in the waters of Solomon Islands C. Listing of tag and recovery data for each tagged skipjack and yellowfin that made an international migration out 65 of or into the waters of Solomon Islands D. Stomach contents of yellowfin sampled by the Skipjack 73 Programme in the waters of Solomon Islands vii LIST OF TABLES Table Page 1 Annual tuna and baitfish catch and effort statistics for the locally based pole-and-1ine fishery in the 3 waters of Solomon Islands 2 Summary of daily field activities in the waters of 9 Solomon Islands 3 Summary of Skipjack Programme baitfishing effort and 10 catch in the waters of Solomon Islands 4 Summary of numbers of fish sampled for biological data 13 from the waters of Solomon Islands 5 Stomach contents of skipjack sampled in the waters of 16 Solomon Islands 6 Incidence of tuna juveniles in the stomachs of skipjack and other predator species from the waters of Solomon 17 Islands 7 The dominant ten species of baitfish caught with bouki-ami gear by the Skipjack Programme in Solomon 18 Islands 8 A comparison of Skipjack Programme baitfish catches for repeat visits to the same baiting localities in Solomon 20 Islands 9 Average bait catch and species composition for baiting areas fished by the Skipjack Programme in the vicinity 21 of The Slot, Santa Cruz Islands and Ontong Java atoll 10 Catch per fishing day for the Solomon Islands pole-and-line fleet in November and June, 1976 to 1980, „ and for the Skipjack Programme tagging vessel in November 1977 and June 1980 in the commercial fishing area 11 Tuna school sightings per hour per fishing day and total catches per fishing day for both surveys by the 24 Skipjack Programme research vessel in the waters of Solomon Islands 12 Indices of fishing performance for tuna schools fished by the Skipjack Programme research vessels during 1977 26 and 1980 surveys in the waters of Solomon Islands 13 Estimates of skipjack growth rates for several countries in the SPC region, by size at release and 29 time-at-large vm 14 Releases of tagged skipjack during 1977 and 1980 in the waters of Solomon Islands, numbers of recoveries made 33 inside and outside the Solomon Islands fishery zone, and numbers of recoveries from unknown recovery locations 15 Numbers of skipjack tagged, total recovered and percentage of tags recovered for sub-areas in the J^ waters of Solomon Islands 16 International recoveries of tagged skipjack for 35 subdivisions of the Solomon Islands tagging area 17 Monthly skipjack tag recoveries by all fishing gears in the waters of Solomon Islands from tag releases in •" other countries 18 Percentage of tag recoveries in the waters of Solomon Islands from releases in Papua New Guinea at locations 40 increasingly distant from the Solomon Islands fishery 19 A comparison of average length of skipjack in the Solomon Islands pole-and-line catch with length of 41 tagged skipjack (recovered in Solomon Islands) at time of tagging and at time of recovery 20 Monthly tag returns, catch and effort for the Solomon 43 Islands pole-and-line fishery 21 Estimates of skipjack population size, turnover rate, throughput and catchability coefficients for the 46 Solomon Islands pole-and-line fishery 22 Fishery interaction results between Solomon Islands and 49 Papua New Guinea 23 Estimated contribution to Solomon Islands throughput by immigrants from tagging locations outside the Solomon 50 Islands fishing area 24 Numbers of yellowfin tagged, total recovered and percentage of tags recovered for sub-areas in the 51 waters of Solomon Islands IX LIST OF FIGURES Figure Page The area of the South Pacific Commission Inside front cover Straight line representations of movements of skipjack Inside back tagged by the Skipjack Programme and subsequently cover recovered Survey area and baitfishing localities for the 1977 and 2 1980 Skipjack Programme surveys in the waters of Solomon Islands Monthly tuna catch by Solomon Islands pole-and-line 5 vessels, 1976 to 1981 Length frequency distributions for tagged and sampled 14 skipjack and tagged and sampled yellowfin for both Skipjack Programme surveys in the waters of Solomon Islands Length frequency distribution of female skipjack from 15 Solomon Islands biological samples and distribution of maturity stages of female skipjack Skipjack school serum esterase gene frequency versus 31 longitude of the sample location Length frequency distributions for sampled skipjack 34 from the Solomon Islands pole-and-line catch during the month of tagging, contrasted with size frequency distributions of tagged skipjack that were released in the commercial fishing area 7 Migration arrows for 18 of 23 Solomon Islands tagged 36 skipjack that made international migrations 8 Migration arrows for 41 of 77 tagged skipjack that made 38 international migrations to the waters of Solomon Islands 9 Relationship between tag recovery rate by Solomon 40 Islands pole-and-line vessels and average distance travelled by tagged skipjack originating from countries (areas) external to the Solomon Islands fishing area 10 Length frequency distributions for skipjack sampled 42 from the June 1980 commercial catch and for tagged skipjack (one school excluded) from the SPC vessel catch, June 1980 11 Solomon Islands monthly skipjack tag returns from Table 45 20, and estimated monthly tag returns from the fitted tag attrition model X 12 Length frequency distributions for tagged yellowfin 52 released during 1977 and 1980 in the waters of Solomon Islands AN ASSESSMENT OF THE SKIPJACK AND BAITFISH RESOURCES OF SOLOMON ISLANDS 1.0 INTRODUCTION The Solomon Islands pole-and-line fishery has developed rapidly in the last twelve years. With a present annual catch of more than 20,000 tonnes, predominantly skipjack (Katsuwonus pe1amis), it now is one of Solomon Islands' three leading industries, as well as the country's major source of foreign exchange accounting for over 23 million Solomon Island dollars of exports in 1980 (Anon 1981a). Clearly the health of this fishery and its interaction with other regional fisheries are of paramount importance to the Government of Solomon Islands. It was concerns such as these, which were shared by many countries in the region, that led to development of the South Pacific Commission's Skipjack Survey and Assessment Programme.