The population dynamics of an intertidal population of Megapitaria squalida was studied from
September 2002 to February 2003 in Bahía Magdalena, Mexico. To obtain information about the artisanal and
recreational fishery of M. squalida, local fishermen at different parts of the bay were interviewed. Clam densities
were determined at one unexploited and two exploited sites along perpendicular transects from the shore line.
Average clam density was 2.01±1.41 ind/m2, densities did not differ significantly between the three sampling
sites. The length-total mass relation was Mtot = 0.0001*SL3.1644 (r2 = 0.9804, n = 92) and the length-tissue mass
relation was Mtis = 0.0002*SL2.7144 (r2 = 0.945, n = 92). Von Bertalanffy-growth parameters were determined
using marked individuals. Strong interindividual and also seasonal differences in growth were observed. Average
annual values were: K = 0.655, L∞ = 83 mm. Since M. squalida can reach a shell length of more than 135 mm
in deeper waters, it is necessary to consider intertidal and subtidal populations separately. Average total mortality
(Z) was 1.61 y-1. No fishing mortality was calculated because total mortality Z at the unexploited control site
was higher than Z at the exploited sites. It appears that M. squalida migrates into deeper water with increasing
shell length, as average shell length increased at lower tidal levels and marked specimens showed a clear migration
towards deeper waters. As yet no overexploitation could be found in the study area. Rev. Biol. Trop. 54 (3):
1003-1017. Epub 2006 Sept. 29.