We have delivered strongly for our clients over the past 17 months advising them on their most important strategic, financial and capital requirements during one of the most uncertain and volatile periods of our lifetimes.
That said, we have learned a lot about operating flexibly over the past 17 months, and we are committed to integrating more flexible work arrangements into the way we work going forward.
The total dollar volume of announced M&A increased 17% sequentially as the number of transactions increased 7% and the average deal size increased 10%.
In fact, the second quarter represents the fourth straight quarter to surpass up $1 trillion in announced M&A activity and the first time ever the trailing 12 months activity exceeded $5 trillion.
Second quarter adjusted net revenues of $691.2 million grew 34% year-over-year.
Year-to-date, adjusted net revenues of $1.36 billion increased 43% compared to the prior year period.
Second quarter advisory fees of $561.4 million grew 67% year-over-year.
Year-to-date advisory fees of $1.07 billion increased 54% versus the prior year period and represent the first time that we have exceeded $1 billion in advisory revenues for the first half of the year.
Our trailing 12-month advisory fees exceeded $2 billion for the first time in our history.
Based on current consensus estimates and actual results, we expect to maintain our number 4 ranking in advisory fees among all publicly traded investment banking firms for the last 12 months and to grow our market share relative to these firms.
In the first half of the year, we also continued to narrow the gap between Evercore and the number 3 ranked firm in terms of trailing 12 months advisory fees.
Second quarter underwriting fees of $48 million declined 49% year-over-year, but excluding two sizable fees during the second quarter of 2020, one from PNC BlackRock and one from Danaher, underwriting fees were essentially flat year-over-year.
Year-to-date, underwriting fees of $127.3 million increased 11% versus the prior year period, even including the PNC BlackRock and Danaher fees.
Second quarter commissions and related revenue of $50.7 million declined 7% year-over-year as both volumes and volatility were lower relative to the elevated levels in the second quarter of 2020.
Year-to-date commissions and related revenues of $104.3 million declined 5% versus the prior year period.
Year-to-date revenues are 6% higher than the first half average of the prior three years, which includes the extreme volatility during the first half of last year.
Second quarter asset management and administration fees of $19 million increased 25% year-over-year as quarter end AUM were $11.1 billion, an increase of 23% year-over-year, principally related to positive investment performance and market appreciation.
Year-to-date asset management and administration fees of $36.8 million increased 21% versus the prior year period.
Our adjusted compensation ratio for the second quarter and year-to-date is 59%.
Second quarter noncompensation costs of $73.1 million declined 5% year-over-year.
Our noncompensation ratio for the second quarter is 10.6%.
Year-to-date noncompensation costs of $145.8 million declined 9% versus the prior year period, and Bob will comment more on noncomp expenses in his remarks.
Second quarter adjusted operating income and adjusted net income of $210 million and $154 million increased 105% and 115%, respectively.
Year-to-date adjusted operating income and adjusted net income of $412 million and $316.5 million increased 122% and 144%, respectively.
We delivered a second quarter operating margin of 30.4% and second quarter adjusted earnings per share of $3.17, an increase of 107% year-over-year.
Year-to-date adjusted margin is 30.3% and adjusted earnings per share of $6.47 increased 136% versus the prior year.
We returned $221 million to shareholders during the quarter through dividends and the repurchase of 1.4 million shares.
Year-to-date, we returned nearly $500 million through dividends and the repurchase of 3.3 million shares, a record level of capital return for our shareholders.
Our dividend -- our Board declared a dividend of $0.68.
We sustained our number 1 league table ranking in dollar volume of announced M&A transactions in the U.S. among independent firms for the 12-month period ending June 30.
We achieved a third straight quarter of advisory revenues greater than $500 million.
And as Ralph mentioned, we surpassed $1 billion in the first half advisory revenues for the first time with strong contribution across capabilities globally, including M&A, capital advisory and strategic defense and shareholder advisory.
We have prominent roles on some of the biggest announcements of the year, including serving as the lead advisor to Grab on its $40 billion SPAC merger, the largest SPAC merger in history and serving as the sole advisor to Nuance on its pending $19.7 billion sale to Microsoft.
Our industry-leading strategic defense and shareholder advisory team continues to be extremely busy and is currently advising companies representing $1.5 trillion in market value in activist defense.
We participated in a number of significant transactions across a variety of sectors during the second quarter, including 31 transactions that raised nearly $10 billion in total proceeds across seven sectors.
And of the ECM transactions that we participated in during the quarter, 60% were as an active bookrunner, including in consumer lead left bookrunner on Post Holdings SPAC; in biopharma active bookrunner on Centessa Pharmaceuticals IPO; and in e-commerce active bookrunner on 1stDibs IPO.
As we mentioned last quarter, our investments in our ECM platform have earned us a place in the top 20 for underwriting revenue as estimated by Dealogic for the 12-month period ending June 30 for deals listed on the U.S. exchanges, excluding bought deals.
We are focused on strategically gaining share and working our way toward the top 10, which is currently comprised of banks that use their balance sheets to win underwriting business.
Finally, assets under management and our Wealth Management business finished the quarter at $11.1 billion as long-term performance remains solid and net new business continued to be positive.
We also have more than 30 SMDs on our platform that have either joined or been promoted within the last three years that represent additional opportunities for growth as they continue to ramp to our high levels of productivity.
For the second quarter of 2021, net revenues, net income and earnings per share on a GAAP basis were $688 million, $140 million and $3.21, respectively.
Year-to-date, net revenues, net income and earnings per share on a GAAP basis were $1.35 billion, $285 million and $6.46, respectively.
The settlement resulted in a gain of $4.4 million, which we have excluded from our second quarter 2021 adjusted net revenues.
Our GAAP tax rate for the second quarter was 22.1% compared to 24.5% in the prior year period.
Year-to-date, our GAAP tax rate is 19.2% compared to 25% in the prior year period.
On a GAAP basis, the share count was $43.7 million (sic) [43.7 million] for the quarter and $44.1 million (sic) [44.1 million] for the first half.
Our share count for adjusted earnings per share was 48.5 million for the quarter and 49 million for the first half.
Firmwide noncompensation costs per employee were approximately $39,000 for the second quarter, down 8% on a year-over-year basis.
This level of noncompensation costs per employee contrasts to our 3-year quarterly average measured from 2017 to 2019 of approximately $47,000 per employee.
We do expect, however, some cost efficiency as we move forward as we utilize the technologies that enabled us to work so effectively over the past 16 months.
As of June 30, we held $1.5 billion in cash and cash equivalents and investment securities, up from the prior quarter as our balance sheet grows throughout the year, as we accrue for compensation obligations that will be paid in the first quarter of next year.
The past 14 years as the CFO of Evercore have been an exciting and challenging journey.

Summary:
Our dividend -- our Board declared a dividend of $0.68.
For the second quarter of 2021, net revenues, net income and earnings per share on a GAAP basis were $688 million, $140 million and $3.21, respectively.