鼠鲨（学名：Lamna nasus），又名大西洋鲭鲨，是鼠鲨科的远洋大型鲨鱼。鼠鲨被认为是处于易危至灭绝的状况，欧洲联盟建议将鼠鲨列入联合国的濒临绝种野生动植物国际贸易公约中。

鼠鲨分布自北美洲东北部海岸（由新泽西州至格陵兰）及非洲西北部海岸、摩洛哥或西撒哈拉及地中海，至冰岛对出的海洋、挪威的北岸及俄罗斯的西北海岸。在南半球，鼠鲨亦环球分布在纬度30°S-60°S的海域。

鼠鲨在世界自然保护联盟濒危物种红色名录中被列为易危。加拿大亦将鼠鲨列为濒危动物。近年在英国海域的过份捕杀亦杀死了大批的鼠鲨。

The porbeagle (Lamna nasus) is a species of mackerel shark in the family Lamnidae, distributed widely in the cold and temperate marine waters of the North Atlantic and Southern Hemisphere. In the North Pacific, its ecological equivalent is the closely related salmon shark (L. ditropis). The porbeagle typically reaches 2.5 m (8.2 ft) in length and a weight of 135 kg (298 lb); North Atlantic sharks grow larger than Southern Hemisphere sharks and differ in coloration and aspects of life history. Gray above and white below, the porbeagle has a very stout midsection that tapers towards the long, pointed snout and the narrow base of the tail. It has large pectoral and first dorsal fins, tiny pelvic, second dorsal, and anal fins, and a crescent-shaped caudal fin. The most distinctive features of this species are its three-cusped teeth, the white blotch at the aft base of its first dorsal fin, and the two pairs of lateral keels on its tail.