Thanks, John, and good morning to everyone listening to the call. I'll begin on Slide 4, which details the changes in the U.S. Treasury yield curve during the first quarter in the upper left-hand chart.
The successful early rollout of the COVID-19 vaccine and improving economic recovery and higher inflation concerns led to a fair steepening move in interest rates, as the short end remained anchored, while maturity 7 years and longer increased approximately 80 basis points during the quarter. This sharp move higher in interest rates resulted in elevated interest rate volatility during the quarter, as indicated by the light blue line in the lower left hand chart. The contrast between interest rates and equity market volatility, as indicated by the dark blue line in the same chart, is notable, as equity markets continue to improve despite the volatility in fixed income markets.
The sharp move higher in interest rates and volatility negatively impacted our agency RMBS valuations, as the resulting increase in mortgage rates and slowing prepayment speed expectations led to lower specified pool pay ups and longer durations on our holdings. Positively, the upper right hand chart displays the impact monetary policy has had on short-term funding rates, which continued to improve during the quarter and is supportive of ROEs for our target assets.
Lastly, in the bottom right chart, we detailed the growth in both commercial bank and Federal Reserve holdings of agency RMBS, which has been consistent and kept valuations relatively rich, despite their under-performance in the first quarter. While expectations for net supply in 2021 have increased to over $600 billion, eclipsing 2020s total of just over $500 billion, we anticipate demand from the Federal Reserve and commercial banks to more than absorb the increased amount, keeping supply and demand dynamics in the sector supportive of valuations in the coming quarters.
Moving on to slide 5, where we provide more detail on the agency RMBS market. In the upper left-hand chart, we show generic lower coupon agency RMBS cumulative performance versus swap hedges since June 30 of last year, highlighting the first quarter of 2021 in gray. As you can see, strong support from the federal reserve and commercial banks drove strong performance in 30-year 2% and 2.5% coupons in the second half of 2020. However, the sharp increase in interest rates and volatility led to under-performance in the first quarter, particularly in late February, before recovering modestly in March.
In addition, specified pool pay-ups, as shown in the upper right, reflected higher mortgage rates and increased expectations of slowing prepayment speeds, as they continued the modest descent that began in the fourth quarter and ended the first quarter sharply lower. The chart in the lower left shows the continued increase in prepayment speeds for lower coupon mortgages during the quarter, as the impact from the increase in mortgage rates in February is unlikely to impact speeds until the report for April is released later today. We expect prepayment speeds and lower coupons to slow meaningfully in the coming months, while higher coupons are likely to decline more modestly and remain elevated as increased mortgage industry capacity focuses on more seasoned loans that had yet to refinance.
Finally, the lower right-hand chart details the implied financing rate for dollar roll transactions in 30-year 2%, 2.5% and 3% TBAs. The implied financing rate is the reinvestment rate for which an investor is indifferent between taking delivery of a mortgage pool or rolling the TBA contract forward 1 month and investing the cash. As indicated in the chart, implied financing rates increased during the quarter, modestly reducing the attractiveness in dollar rolls. Despite this decline, the dollar roll market remains attractive, providing more attractive returns and higher liquidity over specified pools for agency RMBS investors.
Slide 6 provides detail on our agency RMBS investments. As indicated in the upper left-hand chart, in addition to the 15% allocation to agency TBA, our agency RMBS portfolio is well diversified across specified pool of collateral types. We remain focused on lower price collateral stories, mitigating our exposure to elevated pay-ups and historically tight spreads, as our specified pool holdings had a weighted average pay up of 0.5 point as of 3/31, a decline of approximately 0.25 point during the quarter.
We increased our investment in agency RMBS inclusive of TBAs to $10.5 billion during the quarter, reflecting the deployment of proceeds from capital raises during the quarter into the sector. In addition, we continue to optimize the portfolio through active management, rotating out of $5.5 billion of lower yielding specified pools during the quarter, reinvesting proceeds into more attractive, higher yielding pools, underscoring the superior liquidity of the asset class. Lastly, we reduced our allocation to agency TBA investments by $200 million notional, given the modest decline in the attractiveness of the dollar roll market.
Our specified pool holdings paid 6.3% CPR during the quarter, as our relatively newly issued pools had a weighted average loan age of 4.3 months at quarter end. We anticipate expected prepayment speed increases from further seasoning on our holdings will be largely offset by higher mortgage rates, as our lower coupon holdings are no longer refinanced targets. We remain focused primarily in 30-year 2% and 2.5% coupons, as those coupons provide the most attractive combination of lower prepayment speeds and strong support via consistent Federal Reserve and commercial bank demand, but continue to search for attractive higher coupon options to diversify our asset composition.
Our remaining credit investments are detailed on Slide 7, with nonagency CMBS representing 66% of the $138 million portfolio. The modest decline during the quarter is reflective of pay-downs, as the disposition during 2020 have resulted in an appropriately sized unlevered credit portfolio, which represents 9% of our total equity. Our $102 million of remaining credit securities are high quality, with 65% rated A or higher. And we remained comfortable with the credit profile of our remaining holdings. Although we anticipate limited near-term price appreciation, given the significant improvements experienced since the lows were reached in the second quarter of 2020, we believe these assets are attractive holdings, as 100% are held on an unlevered basis and provide attractive unlevered yields.
Lastly, Slide 8 details the growth of our funding book during the first quarter, as shown in the chart on the upper left. REIT purchase agreements collateralized by agency RMBS grew to $8.2 billion as of March 31, reflecting the growth in our total assets, given the successful deployment of proceeds from capital raises during the quarter into agency RMBS assets. Hedges associated with those borrowings remained unchanged during the quarter at $6.3 billion notional of fixed to floating interest rate swaps, as further confidence in the duration of the Federal Reserves accommodative monetary policy stance provided an opportunity to reduce our hedge ratio from 88% to 77% during the quarter. The weighted average interest rate on our hedge book remained unchanged at 41 basis points, while further improvements in the funding rates on our agency RMBS holdings led to a weighted average funding rate of 15 basis points as of March 31.
In order to mitigate the negative impact of rising interest rates on our new purchases, we entered into $1.3 billion notional of forward-starting interest rate swaps with starting dates in 2022 and 2023, concurrent with our expectations for potential adjustments in monetary policy. Our economic leverage when including TBA exposure remained unchanged during the quarter at 6.6x debt to equity, as we remain conservatively positioned given the rich valuations in our target assets.
To conclude our prepared remarks, we are very pleased with the transition of the portfolio since June 30 of 2020 and our ability to restore meaningful dividends for our investors. We believe our cumulative economic return of over 22% since the second quarter of 2020 reflects the benefits of our strategy and management's ability to provide attractive returns to our investors.
The agency RMBS market continues to be well-supported by the Federal Reserve purchase program as well as commercial bank demand. And while agency RMBS spreads appear tight, recent under-performance and bear steepening of the yield curve will benefit investment opportunities, as higher mortgage rates and slowing prepayment speeds provide an improved environment for ROEs in the coming quarters. In addition, monetary policy remains very supportive and we expect that to continue throughout 2021, as the Federal Reserve communicates a desire to maintain an accommodative a stance over the medium term. Lastly, our careful security selection and active management will mitigate the impact of potentially higher interest rate volatility as the Fed approaches an expected tapering of asset purchases in early 2022.
Thank you for your continued support for Invesco Mortgage Capital, and we will now open the line for Q&A.