Net investment income for the first quarter 2013 was $1.3 million, 38% below the $2.1 million recorded in the first quarter 2012. The decrease in investment income in the first quarter 2013 was primarily due to a decrease in the book yield on the portfolio from 2.71% as of March 31, 2012 to 2.66% as of March 31, 2013 and the reduction of the size of the investment portfolio as a result of the commutation payment made to Financial Guaranty Insurance Company in the fourth quarter of 2012.
Realized gains on investments for the first quarter 2013 were $0.1 million. There were no realized gains or losses for the same period in 2012.
Losses and loss adjustment expenses were $0.9 million in the first quarter 2013, contributing to a loss ratio of 13%, compared to losses and loss adjustment expenses of $0.7 million and a loss ratio of 23% for the comparable 2012 period. The decrease in the quarter ended March 31, 2013 loss ratio was primarily attributable to favorable development on RMBS policies.
Acquisition expenses were $1.9 million in the first quarter of 2013 compared to $1.5 million for the comparable 2012 period. The increase in acquisition expenses in the quarter ended March 31, 2013 as compared to the comparable 2012 period was primarily attributable to $0.8 million of acquisition expenses related to the property/casualty business.
First quarter 2013 operating expenses of $1.3 million were $0.5 million, or 25%, below operating expenses in the first quarter of 2012. The decrease in operating expenses for the period ended March 31, 2013 as compared to the first quarter of 2012 was primarily due to a reduction in legal fees.
Total assets of $298.0 million at March 31, 2013 were $0.6 million, or 0.2%, above the level of total assets at December 31, 2012. This increase was primarily related to investment income and an increase in the recoveries of paid losses. Shareholders' equity of $55.4 million at March 31, 2013 was $14.6 million, or 21%, below the level of shareholders' equity at December 31, 2012, primarily due to the net loss in the first quarter 2013. Book value per share was $20.5, a decrease of 22% from year-end 2012, when book value per share was $26.2. Operating book value per share and adjusted operating book value per share, both of which are non-GAAP financial measures, were $49.1 and $66.5, respectively, at March 31, 2013, an increase of 1% and a decrease of less than 1%, respectively, from year-end 2012 when operating book value per share and adjusted operating book value per share were $48.4 and $66.6, respectively. The Company provides information regarding operating book value per share and adjusted operating book value per share because the Company's management and Board of Directors, as well as many research analysts and investors, evaluate book value on the basis of operating book value, the calculation of which includes adding back the unrealized gain or loss portion of the Company's derivative liability, excluding the impact of credit impairments. Please refer to "Explanation of Non-GAAP Financial Measures" below for a description of operating book value per share and adjusted operating book value per share and a reconciliation of those measures to book value per share.