Legault and Ehrhardt: Correcting annual catches from seasonal fisheries for use in virtual population analysis 
289 
given an observed catch of 5,000 fish caught during 
January, June and July, or December and with a con- 
stant N k+1 of 10,000 fish. The resulting annual fish- 
ing mortality rates are also plotted in Figure 7 (top 
panel). The January corrected catches decrease in a 
linear fashion over the range of M, and the associ- 
ated fishing mortality rates decline rapidly as well. 
This decline occurs because the natural mortality 
rate has almost the entire year to change the popu- 
lation before the backward solution reaches Janu- 
Table 2 
True population numbers, observed catch, corrected catch, recorrected catch, and percent bias in population numbers output by 
VPA with the three catch matrices as input for scenario 2. Catch was split evenly between June and July. Years are in columns 
and ages are in rows. 
Catch data for June and July 
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 
498,972 
1,041,839 
2,134,702 
552,040 
1,652,398 
521,608 
288,839 
252,606 
239,144 
518,374 
1,119,232 
288,431 
793,570 
144,699 
110,580 
107,036 
107,278 
251,844 
540,885 
122,597 
77,637 
55,140 
46,687 
47,870 
52,003 
121,428 
229,079 
Observed catch 
138,043 
219,803 
374,142 
69,946 
214,613 
108,991 
118,816 
114,430 
81,561 
145,831 
225,396 
59,580 
267,951 
91,865 
83,072 
59,363 
48,549 
80,383 
177,254 
67,275 
199,969 
41,948 
26,205 
21,918 
16,786 
40,244 
127,221 
31,148 
22,507 
13,067 
9,560 
7,490 
8,310 
28,561 
58,202 
Corrected catch 
143,534 
230,844 
398,149 
71,908 
225,269 
112,829 
123,191 
118,562 
84,035 
151,797 
236,857 
61,124 
282,745 
94,826 
85,615 
60,898 
49,689 
82,802 
185,260 
69,126 
209,559 
42,869 
26,679 
22,289 
17,046 
41,111 
132,074 
31,750 
22,892 
13,257 
9,689 
7,586 
8,419 
29,094 
59,693 
Recorrected catch 
140,605 
223,496 
380,043 
70,958 
217,723 
110,825 
120,889 
117,055 
83,215 
148,562 
229,120 
60,579 
273,342 
93,820 
85,518 
60,869 
49,670 
81,973 
180,784 
68,986 
205,317 
43,193 
26,875 
22,427 
17,120 
41,056 
130,466 
31,998 
23,177 
13,402 
9,783 
7,640 
8,478 
29,296 
59,785 
% bias in population numbers from observed catch 
-2.1 
-2.0 
-2.1 
-2.1 
-2.1 
-1.7 
-1.4 
-2.2 
-2.1 
-2.1 
-2.1 
-2.2 
-2.2 
-1.8 
-2.4 
-2.2 
-2.1 
-2.1 
-2.2 
-2.3 
-2.2 
-2.4 
-2.2 
-2.1 
-2.1 
-2.2 
-2.3 
-2.2 
-2.4 
-2.2 
-2.1 
-2.1 
-2.2 
-2.3 
-2.2 
% bias in population numbers from corrected catch 
-1.0 
-0.9 
0.0 
-2.1 
-0.2 
-2.3 
-2.4 
-1.1 
-1.7 
-1.5 
-0.7 
-2.4 
-0.6 
-2.9 
-1.4 
-1.9 
-2.4 
-2.4 
-1.3 
-3.0 
-1.7 
-1.9 
-2.3 
-2.7 
-3.3 
-3.2 
-2.2 
-4.3 
-2.4 
-2.7 
-3.1 
-3.5 
-4.0 
-4.1 
-3.8 
% bias in population 
numbers from recorrected catch 
0.1 
0.1 
0.1 
0.1 
0.1 
0.0 
0.0 
0.1 
0.1 
0.1 
0.1 
0.1 
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 
0.2 
0.1 
0.1 
0.1 
0.1 
0.1 
0.2 
0.1 
