Thanks for your help guys, much appreciated. Im working on an amphibious fish metapopulation in small forest pools. I was thinking of modelling young versus adults as a categorical variable to get around the single PIM row in a PRADEL model. I would include newly marked fish that were below a certain size as "young" and as "adults" if they were above that size. For each successive time I would adjust the category each fish was in so that "young" fish changed to adult on the next time.
I will check out your paper Bret, thanks for the link!
Happy New Year,
Richard.