The Black Drum is one of my favorite fish to catch and haven't personally seen the "skinny black drums". It"s worth noting and passing along photo's to your favorite game warden if you happen to catch skinny one.
There is a great report published this last April 1st, 2013 by the TPWD about the "Emaciated Black Drum". Their report basically says it is limited to the Baffin Bay area. It was thought that last summer (2012) Brown Tide was causing this emaciation, but their recent report said that the Brown Tide cause was more negligible and overridden with other factors. The good news is that the population is growing.
They compared black drum from Baffin bay and fish caught around the JFK bridge and found on average that the Black drum in Baffin Bay were under weight by 15%. There salinity trends seem to be inconclusive and further study needed to learn about the food supply.
Y'all have a great day of fishin,