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Evaluating population sizes and capture e

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GemmaJF View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GemmaJF Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2017 at 8:01pm
I do agree Rob, I just wanted to point Karen to possible academic papers, that does not mean I am advocate of the methodologies contained within them. Wink The only reason I can see for capturing any of these animals 'en-masse' is to move them during a mitigation. I doubt really even then it is truly justified or does much good in the end.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Vicar Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2017 at 1:16am
Over the last 12 years since I last posted on this thread...(is that possible? where did the time go?)

In Surrey, we have over 100 reptile sites that we've been systematically surveying for almost 10 years (>50K data points). Detection rates for each species vary dramatically by site. I've been trying to correlate the frequency of sightings to conservation status (population dynamics), but I can't do it from sightings alone.

Where habitat has been degraded, you see more animals (less cover to hide in...until they're predated), so that's a negative correlation. There are also year on year fluctuations. Almost the only useable sighting metric is peak count, as there must be at least that many of any species present. It's just not a very useful metric.

You can get population estimates from mark-recapture, which we do for all smooth snakes and increasingly for adder (using at-distance photography for Vb). The practicable solution is going to be a combination, using population modelling based on mark-recapture factors (weightings), probably on a site by site basis. We're not there yet, but we are closer than we've ever been.

A better route may be to look at the area occupied by a species, as this seems to be a far more stable measurement. We're probably too hung up on numbers, although habitat 'quality' for the occupied area is clearly important.

My 2p.
Steve Langham - Chairman    
Surrey Amphibian & Reptile Group
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