Table 12. Estimates of average instantaneous
total mortality (Z) and fishing mortality (F) for combined area silver
hake based on NEFSC survey numbers-at-age data and an assumed natural
mortality of 0.4.
Spring Survey
Fall Survey
Time Period
Z
F
Z
F
1964-1967
-
-
1.40
1.00
1969-1972
-
-
2.03
1.63
1974-1977
1.13
0.73
0.63
0.23
1979-1982
0.83
0.43
0.66
0.26
1984-1987
1.09
0.69
1.11
0.71
1989-1992
1.41
1.01
1.45
1.05
1994-1998
2.87
2.47
1.80
1.40
Estimates for 1964-1972 are based on survey
numbers-at-age data computed with an average of age-length keys for
1973-1975.
Survey Z for the fall is computed as the natural logarithm of the ratio of the
sum from year j-1 to k-1 of age 2+ abundance to the sum from year j to k of age
3+ abundance
Survey Z for the spring is computed as the natural logarithm of the ratioof the
sum from year j to k of age 3+ abundance to the sum fromyear j+1 to k+1 of age
4+ abundance
The estimate of spring survey Z during 1969-1972 was not feasible