Shares of highly shorted shipping firm Zim jumps

** U.S.-listed shares ZIM of Israeli shipping company Zim jump nearly 10% to $10.59

** Shipping stocks rose earlier this week, with Zim hitting a nearly 3-month high after companies diverted their ships away from the Red Sea amid attacks from Iranian-backed Houthi militants in Yemen

** Zim stock up 38% in December, which is shaping up to be its strongest monthly performance in more than 2-1/2 years

** About 24% of Zim's outstanding shares are in a short position, near the highest level in at least 3 years - Ortex

** With the high level of short interest and a rapid price increase, there is a high probability that short sellers are starting to close out positions in Zim, adding extra buying pressure on the stock - James Kosinski, head of sales, Ortex

** Short sellers have made over $100 mln so far this calendar year in Zim but are down $63 mln in December - Kosinski

** Zim's U.S.-listed shares down 44% YTD with a market value of $1.1 bln up to Tuesday's close