Stock Recruitment Relationship - by Jon Kristjansson, www.fiski.com
It is common knowledge that good recruitment leads to stock increase and eventually larger spawning stock. But what about large spawning stock? Is it beneficial for the recruitment?
There are mainly two theories:
The Beverton-Holt model, which says that the recruitment increases with the size of the spawning stock to a certain level, then it flattens out. Further increase of the spawning stock does not lead to higher recruitment.
Then we have the Ricker model, recruitment increases with the size of the spawning stock to a maximum, then recruitment decreases as the spawning stock increases.
Theories are good, but what about the empirical evidence? Now we have data that spans few decades so it is possible to study the real things:
Here is the report on my study of the stock recruitment of several fish stocks in the North Atlantic. By looking at the relative sizes of the parameters over time, I found a clear relationship: The spawning stock and the recruitment oscillate in anti- phase.
Study of the Faroe plateau cod shows inverse relationship of the stock size and the recruitment, and the recruitment is positively related to the growth rate of cod, that is food availability.