Brown Crab lure and rod
Buy the Crab-Fishing Rod ($3) at the Lighthouse shop and cast it with nothing fitted: the rod uses Ham, and 55.6% of Ham bites are Brown Crab.
The other 44.4% are Shrimp, so these two are the whole pool until you buy a Hot Dog.
Drip Brown Crab
Drip Brown Crab exists and rolls the usual 10% per hooked crab, up to 25% with five Wishbone levels.
With more than half the Ham pool, a drip shows up after about 18 bites on average (7 with the full Wishbone), and Ham costs nothing, which makes it one of the cheapest drips in the Fishipedia.
Brown Crab sell price
A Brown Crab sells for $3. It is mainly an early cash top-up on the way to the $57 you need for the Knife and the Beer.
Kill it before throwing it to the keeper; live catches fight back.