Zenith National Insurance Corp. reported fourth-quarter earnings Thursday well below Wall Street’s expectations, causing shares to close down about 6 percent.

Zenith reported income of $39.6 million ($1.06 per share), a 47 percent decline compared with $74.9 million ($2.01) from the same period a year earlier. The company said its results were hurt by a 21 percent decline in net premiums earned. Analysts polled by Thomson Financial were expecting $1.50 per share.

Revenue for the Woodland Hills-based workers’ compensation insurance provider fell 21 percent to $204 million.

The company said that the sharp decline in premiums was due to both a reduction in premium rates as well as increased competition, particularly in California , where premiums earned fell 30 percent, the company said.

Full-year income declined 10 percent to $234 million ($6.27 per share), while revenues dropped 18 percent to $874 million.

Shares in Zenith closed down $2.37, or 5.6 percent, to $39.82 Thursday in trading on the New York Stock Exchange.