One of recreational fisheries managers' biggest problems is that repeat buyers are not a very large component. Saw a paper a couple years ago and, if memory serves, it was something like 30% don't renew. Seems there is a base, which is probably where the harvest is, and lot of folks who try it and don't like it.
Plus, I think the majority of regular buyers are chronologically gifted and not being replaced.
That said, I think Doc's idea should be added for all of the mandatory report requirements. Big game tags, CRCs, crab, all of it.
As I recall the return on summer cards has been about 52%. If one assumes that none of the cards from the 30% of non-renewing crabbers are returned then the potential drops to 70%. Subtract the actual 52% and you have the potential to increase CRC returns by 18% of the total. Note that far fewer winter cards are issued and the rate of return is much higher. The report on the 2016 season will be presented to the Commission this coming Saturday.
Some of the endorsement money was spent surveying those who did not return CRC info and most of those did not crab or caught no crab
which reinforces your perspective that regular crabbers catch the majority of crab and are far more prone to regularly return CRC info.
From a marketing standpoint the loss of 30% of one's customers every year means there needs to be the same number of new customers just to stay even and that comes with its own problems of new crabber ignorance as to regulations and how to crab without losing gear.