offset - transect lines

[Nan Nourn]

Hi Jeff,

Timely news on the new google group! I wanted to ask you about setting up the offset for  distance sampling with line transect data. In your example vignette, the offset is calculated for a point-count site (area of a circle) then converted to hectares (https://doserlab.com/files/spabundance-web/articles/distancesampling#single-species-hds-models)

For a transect line site, would the offset number just be (distance transect line walked * strip-width) if we just wanted to calculate individuals per square kilometer at that site?

Thus, our study area consists of 74 transects with offset being (4km * 0.100km)=0.4

Cheers,

Nan

[Doser, Jeffrey]

Hi Nan,

Yes, that's exactly right. If all transects are 4km and strip width is .1km, then setting "offset = 0.4" in the "data" list argument will give estimates in terms of density (abundance per square km). Note that you can also supply the offset as a vector with a different value for each site if you had transects of different length.

Hope all is well!

Cheers,

Jeff

--

Jeffrey W. Doser, Ph.D.

Postdoctoral Research Associate

Zipkin Quantitative Ecology Lab

Michigan State University

https://www.jeffdoser.com/

Pronouns: he/him/his

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From: spocc-spa...@googlegroups.com <spocc-spa...@googlegroups.com> on behalf of Nan Nourn <nno...@gmail.com>
Sent: Saturday, July 27, 2024 1:40 PM
To: spOccupancy and spAbundance users <spocc-spa...@googlegroups.com>
Subject: offset - transect lines

 

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