This study in America looked at yellow perch caught by anglers. The fish were observed for 48 hours from stream side fibreglass tanks.
Of the 6% of the deep-hooked fish, over a third of them died from their injuries.
"Following will be a series of study summaries conducted by the Fisheries Service that have investigated various recreational fisheries and the release mortality that may be associated with them."
"Fishermen were asked to donate to the study any yellow perch they would normally have released."
"Deep-hooking was defined as being hooked past the gills. Yellow perch were observed for 48 hours in stream-side fiberglass tanks using a flow-through water system."
5.8% OF YELLOW PERCH DEEP HOOKED
"Deep hooking rate was 5.8% and as expected these fish died at a higher rate (35.7%)"
COMPLAINTS OF DEAD AND FLOATING FISH
"When Maryland’s spring trophy season ... The increased popularity of this fishing technique was followed by complaints of dead and floating striped bass near the fishing areas."
TACKLE LEFT IN BODIES
"Examinations of dead fish indicated terminal tackle left in many fish and physical trauma compatible with hook damage."
HALF OF BASS DEEP-HOOKED
"Studies done here in Maryland have determined the deep hooking mortality rate of striped bass caught with conventional J-style bait hooks to be about 50% regardless of temperature, salinity or whether or not the hook is removed (57.7% in 1995; 41.0% in 1996, 56.3% in 1997, 53.1% in 1999 and 58.3% in 2000)."
"Fish subjected to abrupt increases in air temperature when removed from water prior to release (typically in June and July) were more likely to experience fatal disruption of their normal physiology."