At first read it appears that from 2010-2011 the fly fishing category achieved some meteoric growth in participation among all age groups. Unfortunately it appears the data for freshwater fishing and fly fishing were transposed. However, the category still did manage its first positive growth since 2006, attracting just under 200K new participants in 2011.
If you're interested in reading the entire Outdoor Recreation Participation Report you can view or download it here. (pdf)