Altering Clam Densities

Since clam densities in the model are at the high end of those found in nature, we conducted a sensitivity analysis to determine how crab population dynamics might be affected if just clam density was lowered - all other factors kept the same. In the altered model, clam density was 657 (originally 864 #/m$^2$, Table C2) while biomass dropped to 243 from 334 (g/m$^2$). Crab densities decreased for 7-12 and 13-17 instars (0.1068 and 0.0203 versus 0.1106 and 0.0256 #/m$^2$ originally) while 18+ densities increased to 0.0175 from 0.0145 (#/m$^2$). Gut fullness was $\approx 20$% lower (around 0.36 compared to 0.44) and egg production per mature female decreased to 1519 from 1828 (#/# hr) in the original model.

For the model, clam densities are for ALL clams in the estuary. Thus, that model densities are higher than estuary densities is not surprising given that clams below the mesh size used to sieve sediments are missed (Appendix B.3.1). Certainly, if the density of clams were further reduced, food limitation would likely result. However, it is not clam density per se that is important, but clam density across the different clam size ranges which is better reflected by clam biomass.