[MARMAM] Request: information on effect of number, rotation and experience of cetacean observers

alesha naranjit alesha.r.n at gmail.com
Thu Oct 25 08:31:38 PDT 2012


Good day,

I am involved in setting up a long-term (2 or more years) cetacean transect
survey to determine distribution and density of cetacean species off the
east coast of Trinidad in the Caribbean. At the moment our methods require
having two observers (one observing a sector from the vessel heading to 90
degrees port and the other observing another sector from the vessel heading
to 90 degrees starboard) however, sometimes we are only able to have one
observer (observing the same 180 degrees) available on the days that the
boat is accessible to the project.

We are trying to determine if we need to change the method to a single
observer to avoid splitting the data based on the number of observers (as
we have one dedicated observer) or increase the number of observers working
on the project (so we have a pool of 4-6 volunteers available) and rotating
them thus making it more likely that a team of two observers is available
for survey days. We are not sure which would result in more accurate
output.

As such I am trying to find any information on the effect of:

   1. using two observers (one observing a sector from the vessel heading
   to 90 degree port and the other observing another sector from the vessel
   heading to 90 degree starboard) as opposed to a single observer (observing
   the same 180 degrees or 45 degrees to each side of the vessel heading) on
   detection of cetaceans on transect
   2. changing/rotating observers during the project on detections and
   therefore density calculations (as many observers may result in a change in
   detection probabilities throughout the project)
   3. using observers with different levels of experience on the accuracy
   of detections and therefore density calculations (as this may result in a
   change in detection probability throughout the project)

 If anyone is able to provide any information on the above we would be most
grateful.

Best regards,
Alësha Naranjit
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