With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: Females start bearing calves when six to eight years old. Adult narwhals mate in April or May when they are in the offshore pack ice. Gestation lasts for 14 months and calves are born between June and August the following year. As with most marine mammals, only a single young is born, averaging in length and white or light grey in colour. During summer population counts along different coastal inlets of Baffin Island, calf numbers varied from 0.05% to 5% of the total numbering from 10,000 to 35,000 narwhals, indicating that higher calf counts may reflect calving and nursery habitats in favorable inlets. Hybrids have been documented between the narwhal and beluga (specifically a beluga male and a narwhal female), as one, perhaps even as many as three, were killed and harvested during a sustenance hunt. Whether or not these hybrids could breed remains unknown. The unusual dentition seen in the single remaining skull indicates the hybrid hunted on the seabed, much as walruses do, indicating feeding habits different from those of either parent species.
text_B: Given what biologists know (and not just on what could be theoretically possible) about the fertility of narwhal-beluga hybrids, is it at least feasible that a self-sustaining population could form in the wild?
NO.