Wealth management firms were responsible for a flurry of merger and acquisition activity in 2015.

According to the Wealth Management M&A Transaction Report from Boston-based Fidelity Clearing & Custody Solutions, there were 138 mergers and acquisitions representing a total of approximately $145 billion in assets under management.

Most of 2015’s merger and acquisition activity consisted of small transactions: 36 percent of the deals ranged from $100 million to $250 million in AUM, accounting for 6 percent of the total.

One in five transactions occurred in the $1 billion to $10 billion range, accounting for 58 percent of the total AUM -- the largest being the $15 billion sale of a majority interest in Fairfax, Va.-based Edelman Financial Services to Hellman and Friedman in October.

More than 45 percent of the total transactions were concentrated across five states: California, New York, Pennsylvania, Illinois and Maryland. California alone had 21 transactions, or 15 percent of the total activity.

Buying by strategic acquirers and wealth management RIAs accounted for around 84 percent of the total transactions in 2015, with strategic acquirers accounting for 67 transactions, or 49 percent of the total M&A activity. Strategic acquirers are firms who take a financial interest in a wealth manager, then provide guidance and support to help firms grow.

Buying by wealth management RIAs accounted for 49 transactions, or 35 percent of the total.

In 2015, sellers fell into two groups, wealth management breakaways and wealth management RIAs. Of the 138 transactions, RIA sellers outpaced breakaways by a total of 14 mergers and acquisitions.

More than half of all breakaway deals last year occurred in the $100 million to $250 million range, the largest being the creation of New York-based RIA Corient Capital Partners in a $3.3 billion breakaway from Merrill Lynch in September.

For the report, Fidelity researched publicly available information in January 2016 on RIA mergers and acquisitions involving firms with between $100 million and $20 billion in AUM.