An interesting report on hooking mortality along the west coast for coho and Chinook in salt water done by DFO-Canada. Hooking mortality varies depending on gear selection and fishing techniques, fish handling, water temps, etc. Saltwater mortality doesn't appear to push the 50% mark and is generally lower.

http://www.dfo-mpo.gc.ca/csas/Csas/DocREC/1999/pdf/99_127e.pdf