Shell strength in the cockle Cerastoderma edule L. under simulated fishingimpacts

摘要

Experiments were conducted on the cockle Cerastoderma edule L,. to quantify effects of physical impacts on shell damage. The study was prompted by the need to address the information requirements to improve design of mechanical harvesting machines for reducing shell damage and mortality of undersized discards. The minimum free falling distance in air required to damage cockle shells is approximately 0.3-0.5 m. Compression tests at three shell striking points indicated a power curve relationship between shell failure load and shell height and a linear relationship with total animal weight. Large cockles (>25 mm shell height) have a weakened umbo compared with the domed high point, indicating a shell thickness differential at the umbo with increasing age and size. Minimising the free falling distance of cockles in rotary sorting equipment to <0.3 m through the design and installation of deflecting baffles in harvesting machinery may reduce shell breakage and mortality of undersized discards significantly.