Stage-structured analysis and modeling of the Pacific razor clam (Siliqua patula) in a changing environment: investigation of population dynamics and harvest strategies using process models and simulation

Abstract

The Pacific Razor Clam (Siliqua patula) populations along the Washington coast have experienced massive fluctuations in abundance since the 1950s. Since the 1980s, it has been hypothesized that some of the declines in abundance might be related to the disease NIX (Nuclear Inclusion X; Nucleobacter siliqua). This study investigated the relationships between NIX and the processes of survival, growth and recruitment for razor clams along the Washington coast. This study suggests that NIX has not detrimentally affected the razor clam populations along the Washington coast. Contrary to the findings concerning NIX, this study suggests that the processes investigated were affected by the environmental conditions. In particular, survival and growth both showed seasonal components. Similarly, recruitment was correlated to the maximum mean-temperature. However, the degree and direction of the recruitment relationship was beach-specific.Simulation models were constructed to determine whether alternative management strategies could provide greater harvest with little to no change in risk of extinction or loss of recreational harvest opportunity. The current management strategy is a harvest rate strategy in which 25.4% of all clams $>$3.5 inches may be harvested. The simulations suggested that the constant harvest rate strategy was a preferred strategy, but that the rate of harvest could be increased to 80% of the adults with little to no risk to the populations.