The problem I've seen with too many adult shiners in my 1/4 acre pond was zero recruitment of new SMB. I've removed a lot of adult GSH since restocking SMB in my pond as they were competing with the both my newly stocked SMB and and similar sized RES for food. I consider large GSH a competitors for food with similar sized or smaller fish.
2019 110 3-4" SMB stocked
2020 308 5-1/2" to 7" GSH were removed (1232 GSH per acre, mostly in the 6" to 6 1/2" size range)
2021 363 5 1/2" to 7" GSH were removed (1452 GSH per acre, mostly in the 7" size range)
2022 101 6-8" GSH were removed (404 GSH per acre, mostly in the 8" size range)
I have caught a few 6 1/2" to 9" SMB this summer which makes me believe I have had some recruitment. I had huge GSH hatch again in June, lots of 2-1/2 to to 3" shiners going into winter and good numbers of 4" to 5 1/2" from last years huge GSH hatch.
For some odd reason RES recruitment hasn't been an issue with GSH present but SMB recruitment has.
Were I to venture a guess to explain greater resistance of the RES than SMB to GSH predation in fry stages ... it would be these.
SMB are more fusiform (less laterally compressed than than RES). They hatch a little earlier than RES and may not grow any (or much) faster soon after swim-up than RES do. RES may be more fecund and have greater swimup. Shorty's efforts in removing GSH were also probably focused during the time when RES were nesting (something that would provide immediate benefit to RES but would not be soon enough to have benefitted earlier spawns of SMB). Also, the effect on SMB recruitment may benefit RES survival particularly after RES reach sizes beyond the gape of GSH.
FWIW. The gape of an 8" GSH is large enough to accommodate ~0.72" GSH.
