@mintchip
yeah i used my astrologist (also lvl 3) and i considered putting in shell but ultimately decided to put the specific pearl so i wouldnt get a hodgepodge of colors and could systematically acquire pearls of a certain color until i'd gotten 10 of them. also i'm pretty sure trying to encounter more shells (i.e. putting 'shell' into the field) doesn't increase your chances of getting a pearl as much as if you directly increase your chance via putting the specific type of pearl in. also if you put 'shell' in, you'd probably have a lower chance of getting pearls from chests which has happened to me at least twice.
the rng can be incredibly frustrating and rewarding at turns tho. i went for white pearls first and they were a little slow but okay to acquire. pink pearls were like pulling teeth and it took me a ridic number of explores because i kept only getting shells or one pearl at a time or no shells at all on the islands. i've only got black left to go and there was a whole lotta nothing at first but this past island just gave me 2 instances of 2 pearls out of the 2 shells that spawned. so, y'kno, each island and each shell spawn are total coin tosses unfortunately.