Evaluation of hatchery-based enhancement of the mud crab, Scylla spp., fisheries in mangroves: comparison of species and release strategies
Ma. Junemie Hazel L. Lebata A C , Lewis Le Vay B , Mark E. Walton B , Joseph B. Biñas A , Emilia T. Quinitio A , Eduard M. Rodriguez A and Jurgenne H. Primavera AA Aquaculture Department, Southeast Asian Fisheries Development Center, Tigbauan, Iloilo 5021, Philippines.
B School of Ocean Sciences, College of Natural Sciences, Bangor University, Menai Bridge, Anglesey, Wales LL59 5AB, United Kingdom.
C Corresponding author. Email: jlebata@seafdec.org.ph
Marine and Freshwater Research 60(1) 58-69 https://doi.org/10.1071/MF08155
Submitted: 16 May 2008 Accepted: 12 September 2008 Published: 29 January 2009
Abstract
Ranching, stock enhancement and restocking are management approaches involving the release of wild or hatchery-bred organisms to enhance, conserve or restore fisheries. The present study, conducted from April 2002 to November 2005, evaluated the effectiveness of releasing wild and hatchery-reared (HR) mud crabs in the mangroves of Ibajay, Aklan, Philippines where preliminary studies demonstrated declining fishery yields, abundance and size of crabs. Comparison of survival and growth of wild-released and HR Scylla olivacea and HR Scylla serrata demonstrated the effect of nursery conditioning, size-at-release and species differences. Overall yield and catch per unit effort (CPUE) increased by 46% after stock enhancement trials. Recapture rates of released crabs were highest in wild-released S. olivacea and in crabs measuring 65.0–69.9 mm carapace width (CW) and lowest in non-conditioned HR S. serrata. Growth rates were highest for conditioned HR S. olivacea and lowest for conditioned HR S. serrata (11.7 and 3.7 mm month–1 respectively). Fishing mortality was highest for S. olivacea, whereas natural mortality was greater for S. serrata. Conditioning hatchery-bred animals before release is also important in obtaining higher survival. S. olivacea was the more appropriate of the two species for release in mangrove habitats inundated with low-salinity water. However, there is a need for site-specific studies to evaluate the effectiveness of releases.
Acknowledgements
This research was supported by the European Commission, INCO DC grant (contract ECA4-CT-2001-10022). The authors would also like to express their thanks to the SEAFDEC/AQD Mud Crab Hatchery and Nursery Team for providing the hatchery-reared crabs, the crab fishers of Ibajay and Kalibo, Aklan for painstakingly collecting crabs regardless of time and weather and for the assistance during tagging and dissection of tags from recaptured crabs, the Barangay Captains of Naisud and Bugtong Bato, Ibajay and New Buswang, Kalibo for permission to conduct the study in their mangroves, and lastly to the anonymous referees of the initial version of this manuscript for their helpful comments and suggestions.
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