"We are asking tourists and businesses to do this because of their policies on Cape Fur seals," Beauty Without Cruelty spokesperson Anne van Vliet said at a roadside protest in Bryanston, north of Johannesburg.
"The Namibian government has taken a stand that seals are detrimental to fishing populations...and therefore brutally club baby seals to death."
Van Vliet said the reality was that human over-fishing and bad management practices were the causes of declining fish numbers. "Yet they slaughter the pups in the morning, pull the carcasses onto a truck and clean blood on the beaches where tourists later sit.
"We are rather advocating sustainable seal-viewing eco-tourism all year round."
For the last three years, a culling quota of 85 000 seal pups and 6 000 bulls was permitted in Namibia. Bulls were often shot at close-range and their genitalia used as an aphrodisiac.
This, in spite of their Animal Protection Act 71 of 1962, which forbids animal cruelty and beating an animal to death, Van Vliet said.
The group, together with Fur Free SA and Sea Shepherd SA, held the protest under the banner of The Seals of Nam.
Among the crowd were schoolboy Josh, 13, and his four-year-old sister Zeta who attended with their mother Prelene Garreth.
"I brought them here today so they can learn how to preserve the environment as humans naturally destroy it," Garreth said.
"We need to teach our kids these lessons early on...for example Josh is already a vegan."
Local model and actress Christina Storm joined in the protest, saying "it is disgusting that the killing of pups is happening."
"Namibia is our sister country and we love them but we can't allow this to go on... so I'll be boycotting Namibia and its products too," she said.
The Namibian government argues that the seals are consuming 900 000 tons of fish a year, more than a third of the fishing industry catch.
The fishing industry's contribution to the country's GDP was 5% in 2005, according to the Bank of Namibia's annual report of 2006.
The government maintains that the country's seal population is healthy and hunting will not lead to the extinction of the species.