C. pengoi is present in the Bothnian Sea, yet absent/transient in the Bothnian Bay.
Coastal zones appear to be important, with one record in the northerly Bothnian Bay.
Peak abundances recorded in 2006/2007 are the highest reported in the Baltic Sea.
Low biomass of potential prey may contribute to the current C. pengoi distribution.
Climate change factors could modify barriers restricting the spread of C. pengoi.