From their FAQ (http://surlybrewing.com/contact/#faqs pulled June 2015):
"Yes, our beers are vegan friendly. We stopped performing animal sacrifices years ago. But seriously, we don’t use any animal products in the processing of our beer."
From a video interview, December 2011 (http://vimeo.com/33664147) 12:45:
"We just purchased a centrifuge... we're no longer fining our beer, so Surly is officially vegan"
Company email (2008):
yup,
we use the fish.
Email 2 (2008):
Our beers are made with isinglass.
Surly 1349 Black Ale
Vegan
This product is listed as vegan friendly.
What the company told us
Correspondence on record, with the date of each entry.