The Status of Invertebrate Resources at Manihiki and Rakahanga Atolls, Cook Islands. By Ngereteina George & Richard Story September 2014 – Miscellaneous Report: 03/14 Ref No. NG-3/0814 | Inshore & Aquaculture Division Table of Contents Acknowledgments ................................................................................................................................... 2 Summary ................................................................................................................................................. 3 1.0 Introduction ................................................................................................................................. 4 1.1 Pearl oyster (pārau) assessment .............................................................................................. 4 1.2 Trochus (torōkati) assessment ................................................................................................. 4 1.3 Rugose Clam (pa’ua) assessment ............................................................................................ 5 1.4 Sea cucumber (rori) assessment .............................................................................................. 5 1.5 Management and existing harvest regimes ............................................................................. 5 1.6 Objective of the assessment surveys ....................................................................................... 5 2.0 Methods....................................................................................................................................... 6 2.1 Survey design .......................................................................................................................... 6 2.2 Survey methodologies ............................................................................................................. 6 2.3 Data analysis and reporting ..................................................................................................... 7 3.0 Results and discussion ................................................................................................................ 8 3.1 Survey coverage ...................................................................................................................... 8 3.2 Density (all species) ................................................................................................................ 8 3.3 Sea cucumber .......................................................................................................................... 9 3.3.1 Density ............................................................................................................................ 9 3.3.2 Size distribution ............................................................................................................ 10 3.3.3 Stock estimate for selected sea cucumber species ........................................................ 12 3.4 Blacklip pearl oyster (pārau) ................................................................................................. 13 3.5 Trochus ................................................................................................................................. 13 3.6 Manihiki rugose giant clam (pa’ua) ...................................................................................... 13 3.6.1 Density and size structure comparison with previous assessments ............................... 14 3.6.2 Mortality rates ............................................................................................................... 16 3.7 Crown of thorns .................................................................................................................... 17 4.0 Recommendations ..................................................................................................................... 18 5.0 References ................................................................................................................................. 20 6.0 Appendices ................................................................................................................................ 21 Appendix 1. Locations of survey stations. ........................................................................................ 21 Appendix 2. GPS coordinates for stations at each site. ..................................................................... 23 Appendix 3. Summary statistics for the two sites. ............................................................................ 25 Appendix 4. Invertebrate species recorded at the two sites .............................................................. 27 Appendix 5. Summary of MMR unpublished paua data 2002 .......................................................... 31 1 | P a g e Acknowledgments The Ministry of Marine Resources (MMR) acknowledges with gratitude the partnering and financial support provided by the EU Funded Global Climate Change Alliance: Pacific Small Island States (GCCA: PSIS) Project; Environmental Monitoring to Enhance Community Livelihoods and Build Resilience to Climate Change in Low Lying Atolls of the Cook Islands, for the assessment of invertebrate resources in Manihiki and Rakahanga. Many have contributed to the completion of this report from, data collection, analysis, interpretation and writing. Many thanks to MMR Secretary, Ben Ponia, Director of Inshore Fisheries and Aquaculture, Kori Raumea for general guidance, MMR staff, Tangi Napara, Tina Weier, Ravengakore Tuteru, Tuteru Taripo, Wireless Pupuke and part-time MMR staff Maui Tairea, for your efforts in the field and GIS work. Franck Magron, and Ian Bertram of Secretariat of the Pacific Community (SPC), for support in GIS and analytical and guidance in drafting the report. Teina Rongo (National Coordinator for the GCCA: PSIS project) for editorial support. Lastly meitaki kore reka to the Mayors, members of the Island Councils, Executive officers and community of Manihiki and Rakahanga; our work wouldn’t have been successful without your support. Ministry of Marine Resources PO Box 85, Avarua, Rarotonga, Cook Islands T: +682 28721 F:+682 29721 E: [email protected] 2 | P a g e Summary This report presents the results of invertebrate resource assessments completed in May 2014. Transect were used to assess resources over six days in Manihiki and three days in Rakahanga. Sea cucumber assemblages are low in terms of species recorded and size structure. Density of lollyfish was close to regional reference density at Manihiki, but three times higher in Rakahanga, although abundant they were small (average size 122 ±0.9 mm). In Manihiki trochus density was 11.5 (± 6.8) per hectare and absent in Rakahanga. There is no potential for commercial fishing of sea cucumber and trochus at this time. The assessment determined moderate densities of black lip pearl oyster on fringing reefs and patch reefs for both atolls. This data can be added to information currently collected for deep lagoon strata’s in order to estimate total abundance of wild pearl oyster stocks in both atolls. Giant clam is abundant in Manihiki but rare in Rakahanga. When clams stocks are reduced to low levels stock recovery periods are uncertain. To safe guard this important food resource against recruitment failure there is a need to be cautious when determining large scale community harvest. The current prohibition on the exports of clams from Manihiki and the protection of clam stock by Ra’ui is excellent and encouraged. Other tools the council could consider are long term closures, (Ra’ui), minimum size limits and very moderate harvest quantities determined after resources surveys for large scale community harvest. Permanent resource monitoring sites should be established to regularly assess recruitment of juvenile clams. Crown of thorns numbers are very low and do not pose a problem at this time. 3 | P a g e 1.0 Introduction Manihiki and Rakahanga are part of six atolls in the northern group of the Cook Islands. Both atolls are approximately 1,225 kilometres from Rarotonga, the capital of the Cook Islands. Communities on both islands purchase food supplies and necessities in bulk for inter-island cargo ships which can be between two to three months between ship visits. Manihiki is served by inter-island aircraft which visits the island on a fortnightly basis, however occasionally there are chartered flights. Communities commute between atolls by outboard powered aluminium boats. Residents have adapted to the isolation, irregular shipping/aircraft services by primarily living off the sea and land. Manihiki and Rakahanga communities were once heavily involved in pearl production, however due to increased pearl production cost and decreasing pearl value as a result of global trends in production and marketing this activity has subsided to a few fully active farms. Other sources of income include handcraft, export of modest volumes of seafood, small private business and through government employment. Handcraft is primarily produced by women and these valued products are sought after in the Cook Islands. The atolls have significant lagoons with a maximum depth of 70 meters in Manihiki and 33 meters for Rakahanga. The communities carry out similar fishing activities, collecting invertebrates (primarily for clams and lobster), netting, spearfishing, fixed coral fish traps, and several methods of lagoon and deep water hook and line fishing for fin-fish. Fisheries resources are abundant and