Is there any sort of permit required to spearfish other than a fishing license?

No other permit is required.  More information: Spear Fishing in IdahoArchery and Spear Fishing is defined as: Fishing with a bow and arrow, crossbow, spear or mechanical device, excluding firearms. This type of fishing is permitted only in the taking of bullfrogs and unprotected nongame fish and only in those waters during the season set for the taking of game fish. You must have an Idaho fishing license; no other permit is necessary. Game Fish: these species, except for bullfrogs, may not be taken using archery or spear: Brook, brown, bull, cutthroat, golden, lake (Mackinaw), rainbow (including steelhead), splake and Sunapee trout; trout hybrids; Chinook, coho, Atlantic, and kokanee (blueback) salmon; grayling; whitefish; cisco; crappie; perch; bass; catfish; bullhead; sunfish; sturgeon; northern pike; tiger muskie; walleye and sauger; and burbot (Ling). Bullfrogs and crayfish are also defined as game fish. Nongame Fish: Any fish not specifically defined as a “game fish.” may be taken using archery or spear equipment.  Except protected nongame fish (Shoshone, Wood River, and Bear Lake sculpin, sand roller, northern leatherside chub, bluehead sucker and Pacific lamprey) may not be taken by fishing or archery or spear equipment.