Tokyo stocks opened lower Monday as investors locked in gains after the Nikkei index closed at an all-time high late last week. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average fell 186.37 points, or 0.46 percent, from Friday to 40,702.06. The broader Topix index was down 19.84 points, or 0.71 percent, at 2,793.38. On the top-tier Prime Market, decliners were led by pulp and paper, marine transportation and bank shares. At 9 a.m., the U.S. dollar fetched 151.30-31 yen compared with 151.44-54 yen in New York and 151.39-41 yen in Tokyo at 5 p.m. Friday. The euro was quoted …