7116 ‎(2)‎

• UCREFRP Catalog Number: 7116
• Author: Baxter, G. and J. Simon
• Title: Editor
• USFW Year: Series
• USFW - Doc Type: 1970
• Copyright Material: YES

..

Zalewski, M., M. Molinski & T. Penczak, 1975. The
influence of electric currents applied in electrofishing on
the respiration of some fish species. Przeglad Zoologiczny
XIX, 3: 329-334.
Zippin, C, 1956. An evaluation of the removal method of
estimating animal populations. Biometrics 12: 163-169.
Zippin, C, 1958. The removal method of population esti-
mation. J. Wildt. Mgmt 22: 82-90.

Appendix 1

Derivation of equation (10)

For the 2-catch method,

^ C2
q =-
c.

;

If k removals are carried out, q can be estimated from each
pair of catches as

^ Cj + 1
qj=-
C.
I

yielding (k - I) estimates of q. q can then be estimated as the
weighted mean of these estimates. The best result is obtained
if the weighting factor is inversely proportional to the
variance V(qj)' As

V(qJ = V(pJ

and as V(pJ is inversely proportional to Yi (see e.g. eq. (9))
and, hence, inversely proportional to cj, the weighting factor
for qj is Cj. The weighted mean thus becomes

^ Pi ^
q = q. c. + '12C2 + ... qk _ I Ck _ I =
c. + C2 + ... + Ck _ I

~

c2 + c) + ... + Ck

c. + C2 + '" + Ck _ I

= T - c,
T - Ck

,

43

Appendix 2

Proportional probability sampling (P P S)

Proportional probability sampling is carried out in the
following way. First, list the size (area, or possibly length) mj
of all the N units. Then compute the cummulative sum ofmj
and finally the 'assigned range' as in the following example
with N = 8:

r

m. Emj Assigned
I
Range
I 72 72 1-72
2 100 172 73-172
3 37 209 173-209
4 212 421 210-421
5 20 441 422-441
6 91 532 442-532
7 10 542 533-542
8 150 692 543-692

~
r
r
~

To select the first unit, use a table of random numbers and
pick a random number between 1 and 692. Say that this
number is 30 I. As this number is included the 4th unit, the
first sampling section is number 4. The procedure is then
repeated until n units are selected.
PPS with replacement: each unit is drawn independently,
so that the same unit may be included more than once.
PPS without replacement: a unit once drawn is spent; the
same unit is not allowed to be included more than once.

f

r
r.