Of course, fisheries should always be managed in light of the necessity to sustain
recruitment, that is, with the intent to keep plenty of fish active as parents. That we so
often fail to operate under this simple precept is astounding. Sometimes fisheries are
managed with the notion of maximizing recruitment. A model is chosen in which
recruitment peaks below the maximum stock of spawners, and the stock is then
reduced by fishing to the vicinity of that recruitment peak. The best examples are
salmon fisheries. These are in a sense ideal for the purpose, especially if salmon are
fished in or near their natal river, since spawners for the next cycle are the same fish
counted as recruits in the present cycle. They are active in both roles at nearly the
same time. The idea is that to maximize the number of salmon returning to a stream
(recruits) there should have been some optimal number of spawners in the previous
generation (stock). Since the a priori expectation is a domed function, we might guess
that substantially fishing down the number of spawning salmon would actually
increase the number of returning salmon available for the fishery. The argument is
strained because of the separation of the freshwater and marine juvenile phases. It has
to be argued that fewer eggs can produce more and healthier seaward-migrating fry or
smolts by reducing competition in freshwater, and then that the increase in seaward
migrants will improve final adult returns. In some instances, the data are convincing,
in others not. Results for the pink salmon (Oncorhynchus gorbuscha) stock spawning
in the Kodiak Archipelago off Alaska illustrate both cases (Fig. 17.11a & b). If
“recruits” are taken to be fry that are headed for the sea, then the data seem to show
that reducing the stock to 2–3 million spawners does not reduce recruits significantly,
and in some years seems to generate an addition to fry entering the sea of about 1.5-
fold. If recruits are taken to be the adults returning as 2-year-olds, the relation (for
which there are more years of data) is less clear. Two million spawners can return 3
million or 15 million adults to the combined fishery and spawning stocks. Survival at
sea is surely variable and crucial to salmon recruitment.
Fig. 17.11 Pink salmon. (a) Relationship of spawner abundance to 1-year fry (still
freshwater, ready to migrate) for various streams in the Kodiak Archipelago, Alaska.
The curve is a parabola.
(Data from Donnelly 1983.)