Comparing two kernel density maps. It is possible?

[Andreia T. Pereira]

Hi I am Andreia 

I am working with cetacean and fisheries 

I am trying to do kernel density map for total of captures in nets without pingers (control) and other kernel density map for total of captures in nets with pingers (experimental). So I have one problem my effort is a quite different between this two cases (experimental nets have a different effort comparing with control nets). So I need to find a way to include my effort in which case. Can you help me find a solution for this? I want (if it is possible) comparing to maps and take some visual conclusions, for exemple experimental nets reduce a total of captures.

[GIS in Ecology]

Hi Andreia,

Sorry to take so long to answer this post. If you have very different levels of effort between two different data sets, it is not really appropriate to compare kernel density maps (as these assume that the level and spatial distribution of effort is similar).

Instead, I would recommend that you just calculate the captures per unit survey effort using a polygon grid approach. The method is the same as calculating the number of sightings per unit survey effort. 

The exact way that you do this will depend on how your fishing effort is measured. Post back on this thread with information about how you are measuring fishing effort and I will see what I can suggest.

All the best,

Colin

[Andreia T. Pereira]

Dear Dr. Colin

First of all thank you very much for your answer and your kindness trying to help me.

So I will try explain to you. I have different number of effort events between nets without pingers (control nets) and nets with pingers (experimental nets). Taking into account that the event is defined as each time a net is placed and removed from the water. And the effort only includes the number of events. For exemple, I have 400 registered events (launches) in control and 300 registered events (launches) in experimental nets.

The nets used in the control were not the same ones used in the experimental and they were not exactly placed in the same location (but in the same area). I am telling you this because we work in collaboration with fishermen and there are things that we can not control.

Thank you very much,

Andreia Pereira

aftpe...@gmail.com

---

PhD student

CESAM (Centro de estudos do ambiente e do Mar)

University of Aveiro, Portugal

aftpe...@ua.pt

Sociedade Portuguesa de Vida Selvagem (SPVS)/ Portuguese Wildlife Society

University of Minho, Portugal

aftpe...@socpvs.org

--
-- ======================================================================
You received this message because you are subscribed to the "GIS In Ecology Forum" discussion group (http://www.gisinecology.com/GIS_in_Ecology_forum.htm).
 
To control how often you get emails from this group, go to http://groups.google.com/group/gis-in-ecology-forum/subscribe (you will need to log on to get to this page).
 
To post to this group, either log onto the group's home page or send an email to
gis-in-eco...@googlegroups.com.
 
The rules for posting to this group can be found here: http://groups.google.com/group/gis-in-ecology-forum/browse_thread/thread/df31a0822742203f#.
 
To unsubscribe from this group, email:
gis-in-ecology-f...@googlegroups.com
 
All information on this forum is provided on an 'as is' basis. GIS In Ecology is not responsible for checking the accuracy or suitability of any posting or response.
======================================================================
---
You received this message because you are subscribed to a topic in the Google Groups "GIS In Ecology Forum" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/gis-in-ecology-forum/_NgDixvlZUg/unsubscribe.
To unsubscribe from this group and all its topics, send an email to gis-in-ecology-f...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/gis-in-ecology-forum/49d65bc6-d722-4484-95d7-cac43d5163de%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

--