Hi there, there is becoming increasingly common to use the DNA of illegally traded animals for "wildlife forensic science". Wildlife forensic science is the science of identifying wildlife involved in crimes including the illegal poaching, possession or trafficking of protected and endangered animals and plants. Here is some more information about it https://australianmuseum.net.au/blogpost/science/amri-wildlife-forensics-dna
There is no standard procedure for monitoring legal trade. it is mainly done through questionnaire. Every on has to devise own proforma for questionnaire and other data collections.
Hi Sidi - it is impossible to measure how much illegal trade is going on (except estimates)
It is possible to monitor performance of law enforcement - government figures are hard to obtain (and they often do little enforcement) but a network of NGOs in Africa regularly report their progress with investigations, arrests, and sanctions of wildlife traffickers - http://www.eagle-enforcement.org/eagle-briefings-2017/
These law enforcement interventions are done by a team of paralegal experts (NGO) who work with government officials. It's one of the most interesting models of law enforcement that I know about.
You also have the CITES Monitoring of Illegal Killing of Elephants (MIKE) database - https://cites.org/eng/prog/mike/data_and_reports that compiles data from multiple sources.
There is also a coalition of NGOs working to develop standard tools for data collection and analysis - http://smartconservationtools.org/
Look also at the work of Dr Sam Wasser at Washington Uni, http://conservationbiology.uw.edu/ They use DNA analysis to determine where seized ivory comes from and other tools to estimate total illegal trade.
None of the above relate to the Mediterranean but I actually think that some very interesting innovations are coming out of the African continent.