I have been modelling occupancy and abundance of a small stream fish that lives in medium-sized rivers using repeated surveys. One of the questions I am investigating is the importance of various habitat features for adults versus juveniles. I have developed models separately for both life stages but want to look at the probability that the two life stages co-occur in the context of incomplete detection (there are some similarities in important habitat covariates, but detection probabilities and detection covariates differ between life stages). Sample sites are slightly larger than the estimated home range of an adult, there are three surveys at 61 sites within a single season (1 month).
There are potentially three different true occupancy states - adults present with no juveniles, adults and juveniles present, juveniles present with no adults. The presence of juveniles at a site is not necessarily an indication of breeding at the site as there is a brief period of downstream drift prior to transformation into juveniles. Therefore, the multi-state approach doesn't seem appropriate.
I have tried using the multi-species approach setting species A as adults and species B as juveniles, but am wondering if this is indeed appropriate given that it is the same species ( I have some doubts). Any advice that you could provide would be appreciated. Thank you.
Alan