Tazkirul Quran Tafsir : Al-Ma'idah Ayah 96

Hunting is prohibited (haram) while in the state of ihram. This prohibition was ordained, not because of any feature inherent in the thing prohibited, but as a matter of human trial. In order to test man, God chose to ban certain items symbolically. However, wherever the Law-Giver felt that the trial might cause unnecessary hardship to His subjects, the Law was relaxed. For example, for pilgrims who travel by sea or river to the House of God, it is legitimate to fish in the waters and eat the catch if, during the voyage, there is nothing else available to them. Indeed, they have no alternative if they are to save their lives.