288 
Fishery Bulletin 95(2), 1 997 
Discussion 
The value for the corrected catch depends not only 
on when the catch was made but also on the natural 
mortality rate. A low natural mortality rate will have 
similar observed and corrected catches regardless of 
the timing of the catch. The higher the natural mor- 
tality rate, the larger the difference will be between 
observed and corrected catches. Figure 7 shows the 
effect of natural mortality rate on the corrected catch 
Table 1 
True population numbers, observed catch, corrected catch, recorrected catch, and percent bias in population numbers output by 
VPAwith the three catch matrices as input for scenario 1. Catch occurred only in January. Years are in columns and ages are in 
rows. 
Catch data for January 
True population numbers 
1,000,000 
2,000,000 
4,000,000 
1,000,000 
3,000,000 
1,000,000 
1,000,000 
563,368 
522,212 
1,082,210 
2,201,921 
565,560 
1,693,439 
543,652 
288,839 
271,044 
265,450 
564,928 
1,198,526 
306,930 
867,084 
144,699 
123,106 
125,616 
128,107 
290,569 
613,686 
143,831 
77,637 
61,453 
56,899 
60,483 
65,782 
148,527 
286,833 
Observed catch 
136,233 
211,388 
362,172 
66,177 
203,769 
101,578 
107,287 
114,190 
82,873 
147,781 
221,329 
58,318 
258,589 
87,534 
84,210 
62,682 
53,164 
84,144 
182,999 
68,420 
203,312 
42,542 
28,720 
25,385 
19,258 
44,777 
138,012 
34,021 
22,825 
14,337 
11,498 
9,092 
10,137 
33,402 
67,846 
Corrected catch 
111,991 
175,196 
303,765 
53,863 
168,756 
83,123 
87,864 
93,605 
67,631 
121,653 
183,607 
47,405 
215,226 
71,485 
68,736 
50,989 
43,177 
68,681 
151,235 
55,709 
168,370 
34,484 
23,219 
20,508 
15,539 
36,311 
113,478 
27,533 
18,431 
11,556 
9,262 
7,321 
8,163 
27,029 
55,237 
Recorrected catch 
110,092 
170,592 
292,075 
53,315 
164,171 
81,963 
86,593 
92,571 
67,043 
119,430 
178,572 
47,060 
209,129 
70,829 
68,587 
50,892 
43,098 
68,043 
148,001 
55,533 
165,102 
34,655 
23,321 
20,581 
15,575 
36,220 
112,023 
27,636 
18,595 
11,642 
9,322 
7,354 
8,200 
27,116 
55,110 
% bias in population numbers from observed catch 
23.5 23.5 23.5 
23.4 
23.5 
23.8 
24.1 
23.4 
23.4 
23.5 
23.4 
23.4 
23.4 
23.8 
23.2 
23.4 
23.4 
23.4 
23.4 
23.3 
23.4 
23.2 
23.4 
23.4 
23.4 
23.4 
23.3 
23.3 
23.2 
23.4 
23.4 
23.4 
23.4 
23.3 
23.3 
% bias in population numbers from corrected catch 
-1.7 -1.7 -0.9 
-2.7 
-1.1 
-2.9 
-3.0 
-1.6 
-2.2 
-2.2 
-1.4 
-2.9 
-1.4 
-3.4 
-1.8 
-2.3 
-2.8 
-2.8 
-1.9 
-3.4 
-2.2 
-2.2 
-2.7 
-3.1 
-3.6 
-3.5 
-2.7 
-4.4 
-2.6 
-3.0 
-3.4 
-3.8 
-4.2 
-4.2 
-3.9 
% bias in population numbers from recorrected catch 
0.0 0.1 0.0 
0.1 
0.0 
0.0 
0.0 
0.0 
0.1 
0.1 
0.1 
0.1 
0.0 
0.1 
0.0 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
