Enhancing the Recovery of Depleted Tripneustes gratilla Stocks Through Grow-Out Culture and Restocking

Abstract

Grow-out culture in sea cages and restocking were undertaken to help rebuild the spawning population of Tripneustes gratilla in Bolinao, Philippines. Higher population densities and incidence of recruits in 2004–2006, as well as steady increase in the catch per unit effort of gatherers, indicate that the sea urchin population is recovering. Growth of reseeded, hatchery-produced sea urchins in two sites was high and comparable to those in grow-out cages. However, natural mortalities were very high (91–99%). Good growth, high survivorship, and potential reproductive output of sea urchins in grow-out cages, aside from immediate socio-economic benefits, demonstrate that grow-out culture is a cost effective option for reestablishing effective spawning populations. Higher recruitment success in Lucero, compared to other sites, may be attributed to local favorable biophysical conditions and to maintenance of an effective spawning population due to enforcement of marine sanctuary rules, size regulation, and the presence of broodstock cages. Results suggest that the establishment of a network of marine protected areas in tandem with grow-out culture may be strategic in enhancing the recovery of depleted populations by maintaining larval exchange to sustain the productivity of sea urchin fishery stocks along NW Luzon.

Keywords:

• sea urchin fishery
• reseeding
• grow-out culture
• reproduction
• Tripneustes gratilla

ACKNOWLEDGMENTS

The Bureau of Agricultural Research of the Department of Agriculture and the University of the Philippines Marine Science Institute provided the funding and support for research and development of sea urchin culture and management technologies. The field monitoring surveys since 2003 were conducted through the SAGIP Lingayen Gulf project, which is funded by the State of the Netherlands through its Department of Environment and Water of the Ministry of Foreign Affairs, The Hague. We are grateful to Mr. Tirso Catbagan, Christopher Ragos, and Don Dumale for their invaluable assistance and support in the various field surveys and in the hatchery operations; Lambert Meñez and Inggat Laya Casilagan for assistance in the preparation of the figures and review the manuscript; and two anonymous reviewers for their helpful comments on the manuscript. We are also grateful for the cooperation of the people's organization in Victory and Balingasay and other local partners (e.g., fishers, village and municipal officials, sea urchin buyers) in Bolinao, La Union, and Ilocos. This paper is contribution No. 335 of the U.P. Marine Science Institute.