Page 1 of 1

is low constant apparent survival a problem here?

PostPosted: Thu Feb 09, 2023 5:29 pm
by shannonbarbermeyer
Hello, I'm running a POPAN capture-mark-recapture analysis on spotted dolphin data (photo ID data of marked adults) in MARK that were collected during line transect surveys from 2013-2017 with the primary aim being to obtain the Ni abundance estimates within each year. I evaluated the following combinations: survival constant, time varying; detection constant, time varying, and as a function of nautical mile effort; p_ent time varying; and N-hat. The "top" model was constant survival with varying prob of detection (no other models within 2 AICc). For the GOF tests that had sufficient data to evaluate, there were no statistically significant violation issues with heterogeneity of capture and unequal survival probabilities between sampling occasions. The Global GOF test was not significant, no issues of overdispersed data were detected. My question is since we are studying a long-lived mammal with survival that is more often considered close to 1 (and we had no reason during this period to expect survival not to be close to 1 for marked adults) - is the reported estimated constant survival of the model at 65% a problem or is that OK because it is apparent survival and so is also a reflection also of immigration / emigration and not a significant issue when estimating Ni for each year? I am hoping that this is a reflection of us surveying (consistently) just a portion of the expected range of this open population and so the low apparent survival is OK because it reflects the nature of our survey. Most CMR papers using POPAN report survival of various dolphin spp usually close to 1 unless there has been an event like a catastrophic oil spill. (I have read the manual multiple times but I apologize in advance if I missed something that would have helped answer this question. Also, I searched the forum before posting but was not able to find a post that answered my question - my apologies, again, if I missed anything). Thank you very much for suggestions / guidance :) Shannon