I'm trying to estimate the market size of ocean-based recreation,
including scuba, sailing, surfing, jetskiing, etc.  I want to know how
many people participate in these activities and what sales are for
equipment for these activities.

I have access to participation numbers for Boating, Canoeing,
kayaking/rafting, Sailboard, Sailing, Scuba, Snorkeling, Surfboarding,
Swimming, Wakeboarding, as well as historical numbers for many of
these categories.
I also have some more detailed breakdowns by income, age group,
gender, region.

I have retail sales for watersports in general, plus water-ski,
boat/deck shoes, water sport shoes, fishing tackle, boat/motor/access.
breakdowns.
It is quite possible that there are also more retail sales numbers
available, but I can't guarantee it.

However, to answer your question with all of this information would be
far more than a $10.00 answer, as it would take me at least a couple
hours to put together the report alone.