The threshold values for the indicator are defined as the annual average volume of oil introduced to each sub-basin during the selected reference period (Thresholds table 1). The reference period selected for the modern baseline in this indicator is 2008-2013, during which the estimated volume from spills have been at a historically low level (Thresholds figure 1).
Thresholds table 1. Threshold values expressed as volume of oil per sub-basin.
Thresholds figure 1. The estimated volume of oil from detected oil spills and the number of observations and flight hours between 1989 and 2016. The red square identifies the reference period used to determine the threshold value.
It is important to note, that the HELCOM Contracting Parties have committed to the goal of 'No illegal oil spills detected through annual aerial surveillance activities' in the Baltic Sea Action Plan (BSAP), in line with the 1992 Helsinki Convention, and that this goal is aligned with the requirements of MARPOL Annex I. This goal is still to be strived for, and is not substituted by the threshold values used to evaluate this indicator. The threshold values of this core indicator has been derived for the purpose of evaluating the status of the marine environment, and exceeding the target is considered as having a harmful effect on the environment. However, reaching the level of zero spills must still be strived for in the long-term.