さあ！諸君！捕鯨問題だ！

Consider the solution, found using the matrix methods
given in de la Mare (1989), for given values of q1 and M1.
The following equations give the solution for the
recruitment and age-dependent natural mortalities:
q2 = - b1,1 + b1,4 + M1
q3 = - b1,1 + b1,3 + M1
q4 = - b1,1 + b1,2 + M1
q5 = b1,1 - b1,5 + q1 - M1
q6 = b1,1 - b1,5 + b2,1 - b2,2 + q1 - 2M1
q7 = b1,1 - b1,5 + b2,1 - b2,2 + b3,1 - b3,2 + q1 - 3M1
M2 = -b1,1 + b1,2 + b2,2 - b2,3 - M1
M3 = -b1,1 + b1,3 + b2,2 - b2,4 - M1
M4 = -b1,1 + b1,4 + b2,2 - b2,5 - M1
The solution shows that while the differences between
age-dependent natural mortality values can be
determined, the position of the mortality curve can only be
fixed by independently specifying one of the Ma values;
which is equivalent to specifying the average natural
mortality. The solution for the relationship (trend) in year
to year recruitment is dependent on the value of M1. In
summary, being able to determine shape of the
age-dependent natural mortality curve, without fixing its
position, does not lead to a correct representation of the
trends in recruitment. Any error in fixing the position of
the natural mortality curve will lead to errors in the
estimated recruitment trend.

（次説：THE PRECISION OF ESTIMATES USING YEARLY
ABUNDANCE INDICES 　 へ続く）