Mismatch between VMS data temporal resolution and fishing activity time scales

•A mismatch between VMS temporal resolution and fishing activity time scales is identified for fisheries with short fishing trips.•A framework of spatial and statistical tests was developed to quantify possible bias induced by the mismatch.•The framework was applied to the Portuguese purse seine fishery.•For Portuguese purse seiners, bias in trip and fishing set identification renders VMS data ineffective for IUU fishing monitoring.•The bias induced on spatial fishing effort patterns and fishing ground for the Portuguese purse seiners, is negligible.