South Korean shares ended in negative territory for three straight sessions on Tuesday as institutional investors sold stocks to lock in profits after the main index touched the psychologically significant level. The benchmark Korea Composite Stock Price Index (KOSPI) fell 4. 75 points, or 0.24 percent, to close at 1,992.27. Trading volume stood at 191.45 million shares worth 3.41 trillion won (3.28 billion U.S. dollars). Local stocks took a strong start as Wall Street gained ground on positive corporate earnings, but it turned bearish as local institutions sold shares to lock in recent profits. After the KOSPI touched the significant psychological level of 2,000, local institutions sold stocks to lock in profits linked to the equity linked securities (ELS), market watchers The ELS refers to a hybrid debt instrument that is linked to a single stock, a group of stocks or an equity-based index such as the KOSPI. The security should pay returns to investors when the underlying stock index reaches the pre-determined level. Institutional investors sold a net 301.8 billion won worth of stocks, but foreign investors turned into net buyers by snapping up local shares worth 106.7 billion won. Retail investors purchased stocks worth around 200 billion won. Shipbuilder stocks lost ground amid heavy sales by institutional investors. Hyundai Heavy Industries, the world's No. 1 shipbuilder, declined 2.3 percent, and its smaller rival Samsung Heavy Industries shrank 3.3 percent. Top automaker Hyundai Motor slid 1.5 percent, and its affiliate Kia Motors lost 0.8 percent. Market bellwether Samsung Electronics ended steady at 1,370,000 won, but memory chip giant SK Hynix and the nation's biggest steelmaker POSCO ended in positive terrain. The South Korean currency finished at 1,040.9 won against the greenback, down 2.0 won from Monday's close. Bond prices ended mixed. The yield on the liquid three-year treasury notes finished unchanged at 2.87 percent, but the return on the benchmark 10-year government bonds rose 0.01 percentage point to 3.54 percent.