Historical and current status of cockle and mussel stocks in The Wash

Picture credits: Close up photographs of mussels and cockles on the back cover courtesy of the Eastern Sea Fisheries Joint Committee. All other photographs, CEFAS. Introduction 1. Since 1970, previously artisanal fisheries for cockles and mussels in The Wash have been transformed by the rapid introduction of more powerful fishing gears and vessels and the modernisation of processing plant to service increased demand. This has increased the fishing pressure on stocks. The stocks are managed by the Eastern Sea Fisheries Joint Committee using a combination of byelaws and Regulating Order provisions. 2. Since the late 1980s the increased fishing pressure has coincided with declining stock abundance of both mussels and cockles, with negligible spatfall and recruitment of intertidal mussels. Wash bivalve stocks and fisheries were previously among the largest in Britain. 3. This report was initiated under the Wash Forum to determine whether these cockle and mussel stock declines fall within the range of natural long-term fluctuations or if they indicate that the ecosystem has changed from either natural or anthropogenic causes. Fisheries 4. Technical developments in the fisheries and fluctuating international markets have placed increasing pressure on cockle and mussel stocks in The Wash. In the 1970s, trade developed in undersized mussels for relaying abroad, and this was accommodated by a reduction in the minimum legal size in 1982. Subsequently, relaying and dredging of mussels also increased to service markets for both bait and human consumption. Hydraulic suction dredging for cockles was introduced in 1986. This fishery subsequently expanded rapidly without a cockle minimum legal size until 1993. 5. Although the location of mussel and cockle beds in The Wash is similar, the life history, reproduction and population dynamics of the two species show important differences that are relevant to their management. The report provides a summary of the known biology of the two species. 6. In the dynamic environment of The Wash, bivalve stocks are vulnerable to periodic damage from extreme conditions, such as strong tides, northerly storms in winter and occasional cold periods severe enough to produce ice on the intertidal flats. The various beds can be ranked according the risks that they face from these factors. 7. The abundance of mussels in The Wash was surveyed intermittently from 1920 to the mid-1950s, and from the 1980s to the present. Over this period there have been four or five major episodes of change in abundance, commencing with …