Why are dolphins being treated so cruelly in the town of Taiji? As the Porsche and Ferrari you can see in the fishermen's carpark testify, there are substantial profits to be made in hunting dolphins.
The primary motivation for the hunts is the capture of dolphins to be sold live to aquariums for what can be more than AU$100,000 per dolphin. It's a multi-million dollar industry, with international exports alone of over AU$15 million in the past decade. Once a pod has been trapped, dolphin trainers in wetsuits and snorkels arrive to select those dolphins and whales they consider will be best for captivity.
They are taught to do tricks, then sold to aquariums in countries with little or no animal welfare legislation (it is illegal for aquariums in countries such as Australia and the US to acquire dolphins from drive hunts). In dolphinariums in Japan, China and the Middle East, dolphins and whales sourced from Taiji are kept in appalling conditions.
Dolphins and whales deemed not suitable for aquariums are slaughtered for meat. Though demand for dolphin and whale meat is waning in Japan, it is still eaten locally, and a dolphin carcass brings around $600. Young females are particularly sought after for aquariums, and the calves they are separated from are amongst those slaughtered.
The reason the fishermen do not use more humane methods of killing which might be available – such as the use of anaesthesia before death - is simply cost. Their method of killing might be the cruellest, but it is the cheapest.
Only a small group of fishermen are involved in conducting the hunts and slaughters, but there are a number of other commercial beneficiaries, such as the aquariums that purchase the dolphins and the local government-owned Taiji Whale Museum, which brokers the sales (the local government, unsurprisingly, protects and supports the dolphin hunting industry).