Validity of the Subspecies Designation for the Dwarf White Sucker (Catostomus commersoni utawana)

Abstract

A reexamination of white sucker populations originally used to document the subspecies validity and biology of a dwarf white sucker, Catostomus commersoni utawana, provided no evidence of two separate populations of different-sized individuals. Small mature white suckers and larger or normal-sized white suckers still were present, but there was a continuous range of sizes after maturity. After maturity males grew slower than females and had a higher rate of annual mortality. If the size separation originally used to separate the two forms was applied to this study, then all normal-sized white suckers in this study were females and would have had to reproduce with smaller males. Also, no meristic or morphological evidence for justification of a subspecies designation for the dwarf form of white sucker in this lake was found. Because it was also known that considerable variation in the size of white suckers at maturity occurs throughout the range of this species, it was concluded that the existence of a distinct dwarf subspecies has not yet been demonstrated.