Good morning Sam. Sharp eye in examining your output. If your interest rests in the seasonal estimates, then the estimate labelled "Total" is of little interest to you, but happy that you are curious.
The simplest explanation may be rounding. Abundance estimates from
report="abundance" are rounded to whole numbers (because they are abundances, which should be "whole" animals). We don't see the decimal values of the estimated abundances, if
we could average those, they might equate to a value, when rounded, equals 90.
The mystery of the "total" value is caused by your choice of
effort_sum as the
stratification argument in your call to
dht2. Even though you didn't provide the code showing your call to the
dht2 function, the output echo shows that
effort_sum was used.
From what you describe, I wouldn't think
effort_sum is the option to use. Situations in which it is used are fairly exotic. I gather that your need for
dht2 was to apply your sampling fraction. In the situation you describe, I would think that
stratification="geographic" would be the better option for the argument to
An unsolicited comment unrelated to your question: the number of detections per season is relatively small, particularly for point transect surveys where detection function fitting is more difficult than lines. This could be a situation wherein you perhaps
use season as a covariate in the detection function. That model (with 4 or 5 parameters) may be difficult to fit given the 163 detections, but might provide a way to assess if there are seasonal differences in detecability.