Impacts of stock-enhancement strategies on Ostrea edulis in Strangford Lough

• Main Author: Smyth, David Mark
• Published: Queen's University Belfast 2008
• Subjects: 591.7
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486199

A 1998 study estimated the stocks of oysters in Strangford Lough to be 100,000. In 2002 the estimated population was 1 million. Stock's peaked in 2003 at 1.2 million. By 2004 there had been a decline of>300,000 oysters. This decline left an estimated 600,000 in 2005. The decline appears to be the result ofunregulated harvesting. Shellfish gatherers were regularly observed in the present study area. Natural mortality can be disregarded as a cause of decrease since no empty oyster valves were evident. In investigating recruitment potential spatfall surveys were undertaken from June to September 2003 and 2004. The research into spatfall patterns and spatial expansion has identified locations suitable for broodstock sanctuaries and where spat settlement is possible. The findings for 2003-2004 did not detect any shift in the timing ofspatfall since the 1998 survey. Both surveys identified July and August as the months with the highest densities of spat. The highest densities ofoysters (>2m2 ) were recorded on littoral mixed shell (LMX). Sites in the southern basin were coded as (LMX) such locations may be important areas of possible settlement in the future. Investigations into the epibiota on the shell of 0. edulis showed increases in biodiversity are possible during O. edulis restoration. Surfaces ofthe oyster shell showed an increase in species richness and diversity when compared with other hard substrata. Increases in size and age are proportional to increases in species diversity. This work shows that hydrographical conditions the availability ofcultch and the spawning potential ofan un-fragmented stock can augment and rejuvenate the current population. It has collated sufficient base line data to initiate and monitor future restoration programmes. Careful management and policing is ess~ntial for any success. A reclamation and costing plan for any future rejuvenation programmes has also been detailed.