UPDATE 1-Ackman acknowledges mistakes in 2015, details changes in portfolio

(Adds details from investor letter)
By Svea Herbst-Bayliss
BOSTON, Jan 26 (Reuters) - Sitting on a double-digit loss
that is the deepest in his firm's history, billionaire investor
Bill Ackman on Tuesday told investors that he made mistakes last
year in not cutting two big positions but said he sees plenty of
new investment opportunities.
Ackman, whose Pershing Square (N:SQ) Capital Management lost
between 16 percent and 20 percent in its funds in 2015, said it
was a "very costly" mistake that he did not sell drug maker
Valeant Pharmaceuticals International Inc (N:VRX) VRX.TO when the
stock price rose to $200 over the summer.
He also said that right along with Valeant's tumble "the
rest of our portfolio went into free fall which continued up
until the present." His Pershing Square Holdings portfolio has
lost roughly 14 percent this year alone.
But Ackman said he could not sell when he became aware of a
large potential transaction that the Canadian drug maker Valeant
was working on. Valeant's stock price tumbled some 70 percent
amid questions about its business and accounting practices. Now
with hindsight, Ackman said "We should have avoided becoming
restricted to preserve trading flexibility."
Pershing Square ended up selling some Valeant shares at
year's end to take a loss for tax purposes.
Similarly, he feels the firm should have cut its stake in
Canadian Pacific CP.TO when it reached Canadian $240 per share
and he said it was a mistake to buy more shares in Platform
Specialty Products PAH.N at $25 a share to help the company
finance an acquisition.
Ackman said last year's sharp drop reminded investors that
stocks can "trade at any price in the short term" which
underscores why his firm shies away from using margin leverage.
"We expect that there have been many margin loan liquidations in
recent weeks which have contributed to dramatic stock price
declines."
Late last year, Ackman cut the firm's position in candy
maker Mondelez MDLZ.O by selling forward contracts
representing 15 million shares at an average price of $44 a
share. During the summer the firm built a large notional short
position in the Chinese yuan to guard against weakness in the
Chinese economy. But so far, he has made only a modest profit.
Ackman also said that Paul Hilal, a partner at the firm and
Ackman's college roommate, is leaving the firm to pursue his own
venture, which Ackman said he expects to participate in at some
point. As for himself, Ackman is sticking with his firm, noting
that he has no plans to step down.