TAIJI, Wakayama Pref. — As kids in inner tubes bob on the calm waters of this small ocean cove, a 250-kg dolphin zips through the crowd in pursuit of squid tossed out by a trainer.

Niru, a Risso's dolphin caught locally, appears unbothered by all the people and the squeals of surprise and delight. The cove is packed — it is a summer Sunday, and hundreds of families have come.

But in two weeks, the waters of the cove will turn blood red, as it becomes a holding pen for annual hunts that capture and kill hundreds of dolphins each year.