Conservation organisation Sea Shepherd has paid a reward of $11,500 to the person whose information led to the conviction of men who clubbed 23 fur seals to death.
Jason Godsiff and Jemaal Large both admitted killing the seals at a Kaikoura colony in 2010.
Godsiff was jailed for two years and Large was sentenced to eight months' home detention.
Sea Shepherd said the informant, who wishes to remain anonymous, risked their own safety to bring the pair to justice.
