SPCA national chief executive Robyn Kippenberger said it was "appallingly wrong" he had been given home detention.
"What message does that send to people about the importance, firstly of animal suffering, and secondly the importance of this sort of crime.
"People are in prison for smoking marijuana for God's sake.
"This guy has beaten to death 23 animals and left a number of them to die painfully over a number of days. No amount of remorse covers the fact that he was able to perpetrate this act."
She said the Justice Mallon had "missed the point".
"This was a large number of animals, they suffered over a number of days and it was wanton. It was just huge violence towards animals.
"What we find with research is these are the crimes that young people carry out before they go on to commit worse crimes against humans."
Ms Kippenberger said she believed the problem lay in Godsiff being charged under the Wildlife Act, as the crime did not come under the Animal Welfare Act.
She said maximum sentences under the Animal Welfare Act were doubled last year, in recognition of the fact crimes against animals often lead to violence towards people.
Ms Kippenberger, who appeared before a select committee last year which looked at sentences for crimes against animals, said the Wildlife Act was not changed due to grey areas around hunting, fishing and pest control.
"But we do need to look at harsher penalties under the Wildlife Act," she argued, saying the Kaikoura case had given further reason for the Act to be looked at.
She said the attack would have been "extreme terror" for the seals.
"It was absolutely hideous.
"When you think that seals cry when they are looking for their babies - can you imagine the scene? It must have been mayhem.
"It doesn't say much about our community if we are not able to punish crimes like that."