[Basta-users] Monthly capture history; 0 birth or death information

[Ken Honeycutt]

Team BaSTA,



I have 3 questions concerning an analysis I’m working on using BaSTA. I'm
investigating the influence of age on survival of a population of frogs. I
have capture-recapture data on about 1500 individuals from 2 consecutive
years when captures were made only during surveys in June, July and August
of each year.



The first question concerns the capture history setup. I would like to
assign the capture sessions to the survey months rather than years and am
wondering if my following method is reasonable. I set up a capture matrix
with capture sessions 6 to 20. Capture sessions 6, 7, 8 correspond to
capture periods in June, July and August of the first year; sessions 18,
19, 20 correspond with June, July, and August of the second year. Sessions
9-17 correspond to Sept-May during which there were no surveys and I
assigned 0 for all individuals in these occasions. Is this a reasonable way
to set up this matrix, with 0s for individuals during time periods when
there actually was no sampling? As no surveys actually occurred during
sessions 9-17, on first thought I would like to have NAs in these columns
rather than 0s, but BaSTA did not allow this (“NAs are not allowed in
subscripted assignments”).  An additional question that goes along with
this:  If this method does seem reasonable, how does using months instead
of years as the time period change the interpretation on age-specific
survival/mortality? Will it just be months instead of years, or is it more
complicated?



ID

Birth

Death

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

1

0

0

1

0

1

0

0

0

0

0

0

0

0

0

1

1

1

2

0

0

0

1

0

0

0

0

0

0

0

0

0

0

0

1

0

3

0

0

1

0

1

0

0

0

0

0

0

0

0

0

0

0

1

4

0

0

0

1

0

0

0

0

0

0

0

0

0

0

1

0

1

…

0

0

1

0

1

0

0

0

0

0

0

0

0

0

0

1

1

1544

0

0

0

1

0

0

0

0

0

0

0

0

0

0

0

1

0



My second question concerns that I have no information on exact time of
birth or death for the frogs. We know sizes and that all captures are
post-metamorphosis, but nothing specifically about birth or death. I have
read Colchero and Clark (2012) and understand it is not necessary to have
this information for all or even most individuals, though it would be nice.
However, it is not clear if the model is still useful if absolutely zero
birth/death information is available? (Some BaSTA models (e.g., simple
Gompertz) do run and reach convergence with my data)



The last question - perhaps this should be the first question - relates to
length of the study. For the simulation in Colchero and Clark (2012) the
“short” study period is 10 years. Here, my study period is 2 years. Is it
reasonable to draw inference on age-specific survival from this model with
only a 2 year study?



Thanks in advance,

Ken
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