Sutton Harbour, which operates marinas, Plymouth Airport and the airline Air Southwest, fell heavily into losses in the year to March 31 amid fair value adjustments to its property portfolio and tough trading conditions in the transport sector.The firm reported a pre-tax loss of £3.5m in the year to March 31 after fair value adjustments on investment property (which amounted to a deficit of £2.8m). This compared with a profit of £5.5m the previous year, which included a fair value surplus of £2.8m.Revenue rose slightly to £29.3m from £29.2m. Air Southwest had a difficult year as high fuel costs persisted for much of the year, Sutton said."The outlook for airlines is challenging but we benefit from being a tightly-controlled niche operator," the firm said.The company will pay a final dividend of 1p a share, compared with 1.5p a share the previous year. This takes the full-year dividend to 1.9p, down from 2.4p the previous year.