Aspen Insurance Holdings Ltd this morning announced a net loss of $151.7 million in a first quarter in which the company shouldered more than a quarter of a billion dollars in catastrophe losses.The Bermuda re/insurer's after-tax earnings were hit by the earthquakes in Japan and New Zealand, as well as floods and Cyclone Yasi in Australia. These natural disasters resulted in net losses of $255.9 million for Aspen.“The first quarter of 2011 saw an exceptionally high level of natural catastrophes which, combined with historically low investment returns and significant changes implied in new exposure modelling, continue to support a potential improvement in market conditions," said Chris O'Kane, Aspen's chief executive officer."These natural catastrophes had a material impact on our reinsurance segment results, while our insurance segment reported a modest profit in the quarter.”