My knowledge is dated but there were quite a few studies 1970s-1990s which looked at big game poaching rates, detection rates, and conviction rates. Around the country, poaching (defined as illegal harvest) ranged from less than 50% to more than 100% of legal harvest. Detection rates (not arrests or identification of suspects, just detection that a crime was likely committed) ranged from 1% to 10%. Conviction rates as a percentage of poaching was less than 1%.
My guess is that with incentives (e.g., points and cash rewards), an increasingly urbanized population and cell phones that poaching rates may have declined and detection and conviction rates increased nationally. Where there is tribal hunting I suspect detection rates are low, as it is difficult to determine whether an animal was poached out of season or is a legal tribal harvest.
Poaching is definitely a limiting factor when it comes to legal hunting, costing legal hunters both opportunity and harvest. Shorter seasons, smaller bag limits, worse season timing are all means of compensating for poaching losses when legal + illegal harvest is a limiting factor for populations.
