If you actually bothered to read what you linked. You would see this paragraph

The scope of what a Party to the conflict is actually required to do on the basis of Article 18(1) will depend on the interpretation of the qualifier ‘possible’. What will be possible in the circumstances is inherently context-specific. Thus, the measures that must be taken in each case have to be determined in good faith, based on the circumstances and the information reasonably available to both the commanders on the spot or nearby and to the other organs acting on behalf of the Party to the conflict.

And also

In this regard, the fact that the obligation of Article 18(1) applies to the ‘Party to the conflict’ as a whole is critical. Thus, it may occur that the commander of a single warship or even of an entire naval task-force considers, in a good-faith assessment, that it is impossible to undertake, with the assets under his or her command, any of the activities required under Article 18. This does not, however, absolve those overseeing the commander’s operations (who will have a fuller picture of the situation and may be able to deploy other assets) from assessing what ‘possible measures’ can – and therefore must – be taken. Nor does it absolve the commander from considering other activities that are possible, such as alerting nearby coastal authorities or other vessels in the area or making an ‘appeal to the charity’ of neutral vessels in the sense of Article 21.