sharkweeksketchjam.tumblr.com/I don't really use dA anymore, been using tumblr and other sites instead for a few years, and have set up my own swsj for anyone who misses this one.
You can participate if you don't have a tumblr but it likely won't be posted to said tumblr. If you have a blog there, submissions will be open for 2 weeks until next year's Shark Week.