SECTION 1. Section one of Act Numbered Fourteen hundred and ninety-nine, as amended by Act Numbered Six-teen hundred and eighty-five, is hereby amended to read as follows:
""SECTION 1. The use of dynamite or other explosive for the killing or taking of fish, or under water for any purpose except in the execution of bona fide engineering work and the destruction of wrecks or obstructions to navigation, shall be unlawful: Provided, That nothing in this Act shall be understood to interfere with or prohibit the use of mechanical bombs for the killing of whales, crocodiles, sharks, or other large dangerous fishes: And provided, further, That the Secretary of the Interior, upon recommendation of the Secretary of Agriculture and Natural Resources, may issue permits for the use of explosives in taking fish in limited numbers for scientific purposes only."