Last year I sold interests in a publicly traded limited partnership that is held in an
IRA account. Do I need to declare capital gains?

No, it's not taxable - assuming that the LP was held within the IRA, and the proceeds from the sale remain in the IRA, then it is not taxable. At least not yet - if this is a traditional IRA then when you take distrubution(s) you will pay ordinary income taxes on the gain in the account as well as your pre-tax contributions.