there are tons of studies that suggest that gbfisher is right
and there is talk of stopping bass turneys in the fall when bass are real deep
here is a cut and paste from one study
Depth of Capture
When fish are caught and retrieved quickly from deep water, injury may result from
depressurization. Depressurization can result in over-inflation of the gas bladder, inability to
submerge when released, gas embolisms, internal and/or external haemorrhaging and death.
Freshwater fish have one of two basic types of swim bladders. Fish, such as carp, esocids, trout
and salmon have a duct which connects the swim bladder to the alimentary canal. These fish can
expel gas and make buoyancy adjustments more quickly than fish such as, bass, walleye, perch
and most panfish which lack a connecting duct and rely on diffusion to deflate their swim
bladder. Thus, while susceptibility to depressurization varies among fish species, it has the
potential to be a significant source of mortality (Kerr, 2001).
To release fish that suffer from depressurization a technique known as "fizzing" has been
developed to artificially deflate swim bladders by puncturing the swim bladder with a sharp
instrument. In a review of "fizzing", Kerr (2001) suggested that the practice should be
discouraged, as significant damage can result from the procedure, and that fishing deep waters
(5-6 m) should be restricted if fish are intended to be released.
but if you want a good meal of walleye
now is a good time to get them
well not me I can't catch them