 Marten Transport, Ltd NASDAQ:MRTN was the recipient of a large growth in short interest in the month of July. As of July 15th, there was short interest totalling 1,010,000 shares, a growth of 6.0 from the June 30th total of 952,800 shares. Based on an average daily trading volume, of 301,600 shares, the days-to-cover ratio ... 