relationships of size to age and of growth rate to age typically have the forms shown
in Fig. 17.13. There are many considerations affecting the age or size at which it is
most desirable to catch any particular kind of fish. It may only be palatable in a
limited part of its life span. In fact, the eggs may be the target of the fishery: caviar,
herring roe, and urchin ovaries are prized delicacies. A fish may need to reach a given
size before it can reproduce significantly, or the most desirable growth rates may be
confined to a narrow age span. In the latter case, it might be desirable to remove the
fish in older, larger categories so that their slow, inefficient growth does not “waste”
fish food. Accounting for growth potential in management means adjusting the size
(age) at recruitment so that fish growing at substantial rates remain in the field making
meat for eventual harvest. The trade-off can be that more time to grow is coupled with
more time for natural mortality, which reduces the final take.
Fig. 17.13 Length at age for larval Atlantic cod (Gadus morhua) from Georges Bank
(^) (after Green et al. 1999).
Inset: length of cod at age 4 years and greater that are recruited to the Greenland
fishery
(after Riget & Engelstoft 1998).
There are also moderate differences in growth among year classes.