50 years of estuarine cockles (Cerastoderma edule L.): Shifting cohorts, dwindling sizes and the impact of improved wastewater treatment

Bivalve populations are prone to change due sudden or gradual alteration in the natural environment and anthropogenic interference. Fisheries environmental managers therefore interested long-term trends disentangling human influences, assisting them conservation efforts management of bivalve stocks. Here, 64 monitoring reports covering a 50-year period from 1958 2009 cockles Cerastoderma edule (Linnaeus, 1758) South Wales, UK, were scrutinised for data on recruitment, growth mortality. Changes these population parameters related modernisation wastewater treatment 1997, weather climate variables (temperature, sun hours, air frost days, NAO) numbers estuary. Recruitment as well mortalities high during first last decade study, variation was significantly linked total number population. Cockle sizes all cohorts overall biomass declined late 1990s. Modernisation with downward trend, suggesting that changed nutrient regime estuary may have resulted reduced food provision cockles. The average size newly settled their mortality: smaller recruits higher study indicated link between 1997 diminishing cockle shortened life span. Survey methods profoundly after 2009, it is recommended develop conversion factors pre- post-2009 survey methods. This would allow an extension timeline deeper insight into impact recovery