248
Exercise 18
Table 18.1. A useful table for recording results from the Schnabel method.
Total
Total
number
Number of
Reference,
number
Number
marked in
marked
trial number,
captured
marked and
population
recaptures
~(SM)
and date
(S)
returned
(Ma)
(S)(M)
~(SM)
(R)
~(R)
-
=N
~(R)
aAt time of sample.
THE SCHNABEL METHOD
PROPORTION
CAPTURED
The Schnabel method weights individual Petersen averages throughout the study
period:
Note that marked organisms must be returned to the population for possible
recapture a second time, or more. In addition to all assumptions applying to the
Petersen method, this method assumes no mortality. Table 18.1 may be useful in
executing the Schnabel method.
100~-----------------------'-THE INTERSECTION OF THE
ABCISSA BY A PERPENDICULAR
LINE PROVIDES AN ESTIMATE OF
THE TOTAL POPULATION SIZE.
(R/S AS 'X,)
50
o~------------------------~-- M
CUMULATIVE NUMBER TAGGED
(PRIOR TO THAT SAMPLE)
Figure 18.1. The Schumacher-Eschmeyer plot.