They don't sample only eggs and larvae. That is one section of the stock assessment. The other major section is that they do take landing data. I've done a sampling for them in the past.
We'll do a sample of approximately 200 fish. We measure all 200 fish, and then from those 200 we do a subsample, in which we keep two fish from each half-centimetre size class, and those fish are shipped off to DFO so that DFO can evaluate the age structure from that subsample of fish.