Help with two recapture occasions!!

[Puig]

Hi my name is Héctor, and I’m working with gray whale calf abundance estimation from shore-based sighting surveys, and I have to estimate the recapture rate (detection rate) based on the mark-recapture data from replicate counts. I’ve been reading the Mark manual and I still have some doubts in getting some of the parameters. I have to say that this is the first time that I use the Mark program so that’s why I’m asking for your help. I only have two occasions, but the thing is that I have trouble with the β term, so that’s why I haven’t been able to see differences between both Ф and p parameters. Just to see how the program works I ran the four basic models but the output results are the same for all of them and their deviance is 0 and I don’t know what I’m doing wrong.
I hope you can help me.

Thanks

Héctor
México.

[cschwarz@stat.sfu.ca]

Hi Hector.

Before going too much further, could you please provide a more detailed description of your study design?

You mention that you only had 2 survey occasions. This would seem to indicate that some sort of Petersen experiment was done. With two survey occasion, you can't estimate phi in a Petersen experiments as you must assume that the population is closed.

But you also indicate you have replicate counts? Do you mean you have repeated counts at each sampling occasion (some sort of robust design).

How were your whale calves "marked". Are you using photo-identifcation, in which case some of the mark-recapture methods with mis-identification may be useful.

Carl Schwarz