Effects of mesh size on estimation of population densities of tropical euthecosomatous pteropods

Euthecosomatous pteropods were collected in successive oblique plankton tows with 1 m diameter nets equipped with No. 0, No. 6, and No. 20 nylon mesh. Comparisons of samples revealed that the same species were collected by all 3 nets, but the No. 0 and No. 6 nets failed to collect veligers and juveniles of Spiratella inflata and Creseis virgula conica. Collections with nets of larger mesh size may erroneously suggest seasonal variations in population densities due, not to actual changes in total density, but to changes in the size of individuals and changes in the relative numbers of the different life stages. A large diameter net equipped with No. 20 mesh is recommended for work that includes the smallest life stages of tropical pteropods.