Hawaiian Electric Industries’ earnings rose sharply in the fourth quarter from the same period a year earlier, but the gain was mostly due to an unusually poor performance a year earlier when the company wrote off losses from mortgage securities.

HEI said it earned $24.7 million, or 26 cents a share in the three months ending Dec.  31, up from  $13.7 million or 15 cents a share in the year-earlier period. Excluding the writing off of mortgage-related losses, HEI would have earned $33 million or 36 cents a share in the fourth quarter of 2009.

For the full year HEI reported earnings of $113.5 million, or $1.21 a share, up from $83 million, or 91 cents a share in 2009. Excluding the mortgage liquidation HEI would have earned $102.3, or $1.12 a share in 2009.

“This was a solid year for HEI as we demonstrated improved profitability and earnings and reduced risk,” said President and Chief Executive Officer Constance Lau.

Net income at HEI’s American Savings Bank unit totaled $58.5 million in 2010, up from $41.1 million in 2009 excluding the mortgage charges.

HEI’s Hawaiian Electric Co. subsidiary produced net income of $76.6 million in 2010, down from  $79.4 million in 2009. The company attributed the decline to lower electricity sales, higher maintenance expenses and an increase in financing costs.

The results were released after the market closed.