April 21 (Reuters) - Insurance giant Chubb CB.BN reported an 81% rise in first-quarter profit on Tuesday, buoyed by robust investment returns and lower catastrophe losses.

Insurers usually invest a portion of their capital across different asset classes, including fixed-income securities and equities, with returns often mirroring broader market trends.

Here are some details:

• Net investment income on a pre-tax basis surged 9.5% to $1.71 billion in the quarter from a year earlier. Investment income currently represents more than half of Chubb's earnings.

• Catastrophe losses were $500 million on a pre-tax basis, compared with $1.64 billion a year earlier, which included $1.47 billion from the California wildfires.

• "Both property and financial lines insurance market conditions are soft or softening, with portions of the property market softening at a rapid pace," CEO Evan Greenberg said.

• Core operating income was $2.69 billion, or $6.82 per share, in the three months ended March 31, compared with $1.49 billion, or $3.68 per share, a year earlier.

• Chubb's property and casualty insurance arm combined ratio was 84% in the quarter, compared with 95.7% a year earlier. A ratio below 100% means the insurer earned more in premiums than it paid out in claims.