Spawning seasonality of hilsa (Tenualosa ilisha) in Myanmar’s Ayeyarwady Delta Annabelle Bladon, Kyi Thar Myint, Thida Ei, Myint Khine, Pwint Thu Aye, Thida Lay Thwe, Kimio Leemans, Khin Maung Soe, Michael Akester, Eugenia Merayo and Essam Yassin Mohammed Working Paper Fisheries Keywords: September 2019 Economic incentives for marine and coastal conservation, Biodiversity and conservation, hilsa, marine conservation, oceans About the authors Annabelle Bladon, researcher, IIED; Kyi Thar Myint, assistant lecturer, Yangon University; Thida Ei, lecturer, Yangon University; Myint Khine, assistant lecturer, Yangon University; Pwint Thu Aye, assistant lecturer, Yangon University; Thida Lay Thwe, professor (head), Yangon University; Kimio Leemans, researcher, WorldFish Myanmar; Khin Maung Soe, national programme advisor, WorldFish Myanmar; Michael Akester, country director, WorldFish Myanmar; Eugenia Merayo, researcher, IIED; Essam Yassin Mohammed, head of Blue Economy, IIED. Corresponding author email: [email protected] Produced by IIED’s Shaping Sustainable Markets group The Shaping Sustainable Markets group works to make sure that local and global markets are fair and can help poor people and nature the thrive. Our research focuses on the mechanisms, structures and policies that lead to sustainable and inclusive economies. Our strength is in finding locally appropriate solutions to complex global and national problems. Acknowledgements We would like to thank the fishers, fish collectors and township Department of Fisheries staff who assisted with the collection of the data that formed the basis of this report. We also thank the Ayeyarwady Region Department of Fisheries and the Myanmar Fisheries Federation for their support, and recognise the contributions of WorldFish and the CGIAR Research Program on Fish. Finally, thanks to Dr Jalilur Rahman for his helpful comments. Published by IIED, September 2019 Annabelle Bladon, Kyi Thar Myint, Thida Ei, Myint Khine, Pwint Thu Aye, Thida Lay Thwe, Kimio Leemans, Khin Maung Soe, Michael Akester, Eugenia Merayo and Essam Yassin Mohammed (2019) Spawning seasonality of hilsa (Tenualosa ilisha) in Myanmar’s Ayeyarwady Delta. IIED Working Paper, IIED, London. http://pubs.iied.org/16661IIED ISBN: 978-1-78431-742-3 Printed on recycled paper with vegetable-based inks. International Institute for Environment and Development 80-86 Gray’s Inn Road, London WC1X 8NH, UK Tel: +44 (0)20 3463 7399 Fax: +44 (0)20 3514 9055 www.iied.org @iied www.facebook.com/theIIED Download more publications at http://pubs.iied.org/ IIED is a charity registered in England, Charity No.800066 and in Scotland, OSCR Reg No.SC039864 and a company limited by guarantee registered in England No.2188452. IIED WORKING PAPER The hilsa is a critically important species for small- scale fishing communities in Myanmar’s Ayeyarwady Delta and Rakhine State. Yet current fishing regulations are inadequate and exploitation rates are well beyond sustainable levels. This study analyses key parameters underlying hilsa biology, comparing them across different ecological zones of the hilsa’s range in Myanmar and across time. It provides evidence of major spawning activity between July and September in the freshwater zone, particularly in September. We recommend that policymakers restrict access to fishing in freshwater areas at least during the month of September; promote and enforce measures to protect juvenile hilsa; establish marine protected areas to conserve spawning stock biomass; and ensure effective, adaptive fisheries management throughout migratory routes. Contents Summary 4 4 Conclusions and recommendations 23 4.1 Current fishing restrictions do not 1 Introduction 6 coincide with hilsa spawning season 23 4.2 Freshwater nursery grounds require year- 2 Methods 8 round protection 23 2.1 Study sites 8 4.3 Marine protected areas could support 2.2 Sampling and dissection 9 spawning stock 24 2.3 Length and weight 10 4.4 Migratory routes must be maintained 24 2.4 Gonadosomatic index 11 4.5 Management should be adaptive 24 2.5 Maturity 11 4.6 Research gaps 24 2.6 Sex ratio 11 2.7 Data analysis 11 Appendices 25 3 Results 12 Acronyms and abbreviations 30 3.1 Length and weight 12 Glossary 31 3.2 Gonadosomatic Index 15 3.3 Maturity 18 3.4 Sex ratio 21 www.iied.org 3 SPAWNING SEASONALITY OF HILSA (TENUALOSA ILISHA) IN MYANMar’S AYEYARWADY DELTA Summary The hilsa is a crucially important resource for small-scale The gonadosomatic index (GSI) represents the relative fishing communities in Myanmar’s Ayeyarwady Delta and weight of the gonad to body weight. This study focused adjacent Rakhine State. Yet current fishing regulations on female fish, which have a larger gonad size and are inadequate and rates of exploitation are well greater variation in gonad weight over the course of the beyond sustainable levels. In Bangladesh, the effective reproductive cycle. Mean female GSI values varied most enforcement of fishing restrictions to protect spawning in the freshwater zone, indicating that more brood fish hilsa and the creation of sanctuaries in nursery grounds congregate and release their eggs in this zone. Peaks are thought to have contributed to an increase in hilsa in mean GSI values (indicating a larger number of fish production of more than 100% over the last 15 years. with ripe gonads) were observed in the freshwater zone in July, April, and November 2018, probably suggesting To be effective, fishing restrictions must be based more than one spawning season. A steep dip in the on an understanding of the reproductive biology of mean freshwater GSI values between the highest peak hilsa, particularly their size at first maturity, the onset in July to the lowest trough in September, combined and duration of spawning seasons, and the location with a parallel drop in length–weight relationship of spawning grounds. Any restrictions must not only parameter b, indicates that August–September is the coincide with the main spawning season, but also last main spawning season. In brackish water, mean GSI long enough to allow sufficient spawning. This study values peaked in June and November 2018, indicating analyses key parameters of hilsa biology across the that gonads have grown as fish migrate upstream for species’ migration route, in order to develop a more spawning in freshwater. Mean female GSI values were detailed picture of hilsa reproduction in Myanmar and to least variable in the saline zone, with peaks in February determine the optimum timing for fishing restrictions. and November 2018, which could be an indication From November 2017 to November 2018 (inclusive), that gonads have begun to grow with the initiation of samples of hilsa were taken on a monthly basis from spawning migration. sites in the three ecological zones: fresh water, brackish Within the saline zone, mature fish (80%) were water and saline water. We assessed seasonal and much more abundant than immature fish, whereas spatial patterns in the length–weight relationship, in fresh water, immature fish predominated (77%). gonadosomatic index (a measure of reproductive This highlights the importance of fresh water as a capacity), sex ratio, and maturity of the hilsa. Together favourable habitat for spawning and as nursery grounds these parameters were used to assess spawning for immature hilsa before they migrate downstream behaviour and provide a robust basis for effective through brackish waters to reach maturity in coastal fishery management. waters. Across all ecological zones, the percentage The hilsa specimens caught in fresh water were abundance of immature hilsa peaked in December significantly smaller and lighter than those caught in (59%) and November 2018 (55%), and was lowest in brackish and saline water. This indicates that hilsa June (6%), which is consistent with major spawning spawn in the freshwater zone, which also provides a activity occurring in August–September. In the nursery area for juveniles before they migrate towards freshwater zone, where most spawning activity occurs, the coast, where they reach maturity. The females immature hilsa were most abundant in August (93%) caught in brackish and saline water were heavier and September (94%), declining to a low of 27% in and larger than other specimens, indicating that they April. This could be evidence of additional spawning migrate from the saline zone through the brackish zone seasons in January–February and April–May. In brackish to fresh water, where they release their eggs (resulting water, the percentage abundance of immature hilsa in significant weight loss). In these areas, females peaked in November 2018, probably reflecting their were heavier than males, owing to their greater gonad migration path towards the sea after spawning in August weight. Negative allometric growth (exponent parameter and September. b < 3) was observed in September, indicating that The sex ratio of hilsa samples can provide an fish had released their gonad products at this time. indication of where and when male and female hilsa This suggests that September is a significant month gather together. Overall, and in fresh water, females for spawning. predominate over males, while in brackish and saline 4 www.iied.org IIED WORKING PAPER waters, sex ratios are more equal. Among immature • Marine protected areas could support spawning hilsa, females predominate over males, whereas the stock. We recommend the creation of no-take ratio is closer to 1:1 for mature hilsa. This could reflect marine protected areas to protect mature