I'd wager the spamming is performed by a person, not a bot. Thus a captcha (a real captcha that changes, not the static one used with the blog) would be effective at minimizing spam.
This is precisely why a captcha would be relatively ineffective at stopping committed spammers. Captchas were designed to defend against bots, not people. If I wanted to fill up several pages of the forums with spam, the captcha would simply slow me down a bit between each topic.
Although it could actually be effective against anonym, since he probably would fail most of them.
We need a server-sided timer between topic creations, like I said above.
Edit: @Ben yes.
Edited 7/7/2016 15:58:24