Although four of the 48 sea otters captured to date have died, U.S. Fish and Wildlife Service experts said they will continue efforts to establish a breeding colony of the threatened species in the waters off San Nicolas Island. In all, 70 otters are to be relocated from the San Luis Obispo coastline to the island 70 miles southwest of Los Angeles as a hedge against an oil spill that could wipe out the primary populations along the coast. Authorities said the four otter deaths over the weekend were not unexpected. They suspected stress was the cause.