Boston Symphony Orchestra hired Brookside to replace Tyndall Institutional Partners as an absolute-return manager for its $160 million core endowment, said Thomas May, director of finance and business affairs. Brookside will run $6.5 million, funded from the terminated $7.5 million Tyndall portfolio. The allocation for the remaining $1 million is undetermined. Staff changes at Tyndall brought about the decision, he said. Jeff Halis, a partner at Tyndall, did not return phone calls by press time.