Extremely low PENT values for one site!

questions concerning analysis/theory using program MARK

Extremely low PENT values for one site!

Postby AndrewM » Fri Jun 23, 2017 7:33 pm

Hi

Am analysing a freshwater turtle tracking study data. The turtles were caught in fyke nets in a flowing river. There are 4 sites that are 40 km apart. There have been recaptures at the upper 3 sites, but not the lower sites as this site has both lower numbers and a low abundance of females caught in the nets.

The PENT values for the two upper sites are similar (~0.035), however the PENT for the 2nd lowest site is estimated to be (0.88*10^-15) regardless of model. The river at the lower two sites is much broader, with longer reaches that are spatially larger and therefore a larger area for the nets to try and capture individuals over. Is this potentially what is happening? Just a much lower probability of entry to the population caused by reduced probability of individuals intercepting the net compared to the more spatially restricted upper to sites?
AndrewM
 
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Re: Extremely low PENT values for one site!

Postby Eurycea » Mon Jul 10, 2017 3:58 pm

You are trying to calculate site-specific PENT values for sites that have no recaptures, is that correct? Generally speaking, recaptures are what allows one to calculate parameters using capture-recapture models. Without any recaptures, you don't have the requisite data for these models.
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Re: Extremely low PENT values for one site!

Postby AndrewM » Tue Jul 11, 2017 11:36 pm

No, all these sites have recaptures, all other parameters appear normal between sites.
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