Capelin in the Barents Sea are primarily harvested in a terminal fishery that targetsmaturing individuals. Theory predicts that, in a semelparous population (i.e., one inwhich reproduction is seasonal, synchronous, and followed by parental mortality), anunselective, terminal fishery (i.e., one in which most of the fish that are not caughtwill not have a new spawning opportunity) does not generate strong selection for changedage and size at maturation. The probabilistic maturation reaction norm (PMRN) method wasapplied to test this prediction and to detect possible temporal changes in length atmaturation of Barents Sea capelin between 1978 and 2008. Maturation reaction norms suggestthat maturation is age-independent in capelin, but that males require a larger size toattain the same maturation probability as females. No temporal trends in length atmaturation could be detected, thus confirming the theoretical prediction. Furthermore,none of the candidate environmental variables tested to explain the temporal variabilityin length at maturation (water temperature and capelin biomass) consistently showed asignificant correlation with the PMRN midpoints.