Michael Weaver, former global head of securities lending at BlackRock Inc., has joined Citadel as a chief operating officer in one of its stock-trading units. Weaver, who left BlackRock in December, started at Citadel’s Surveyor Capital equity group on Monday, said Zia Ahmed, a spokesman for Citadel. Surveyor is one of four units that trades equities at the firm, with each feeding into its main Kensington and Wellington hedge funds. The Surveyor unit...