The RSPCA accused the show of killing pigs for entertainment.
A spokesman said: "The RSPCA opposes practices that cause animals pain, suffering or death in the name of entertainment. It's unacceptable and could easily cause great distress to the animals. There's no excuse for using animals in stunts that carry a high risk of them being harmed."
Animal rights charity Peta said: "Killing animals is a cheap ratings ploy and sends an especially harmful message to young viewers, who are greatly influenced by what they see on TV. Bear Grylls and the producers should be prosecuted. Fame doesn't mean immunity."
Commentators on Twitter shared their outrage.
Earlier in the series, contestants killed an endangered American crocodile, thinking it was a common caiman.
A Channel 4 spokesman said: "All islanders were trained in the humane capture and dispatch of animals. They decided they needed to eat or risk being unable to continue."
It's not the only outcry over Grylls' new show: viewers complained of feeling sick during season one of the show when two contestants were administered painful enemas.
It has already faced accusations that part of the show had been staged along with accusations that those taking part in the reality show had taken part in similar survival challenges and were not "ordinary men".
There were claims of sexism when the show was first announced, with its all-male cast for season one criticised.
The first season of the show aired on TV One in New Zealand.
- Daily Mail