Investable hedge funds fell by 2.37% in July, according to the latest numbers from RBC Capital Markets.

Just one of the nine strategies tracked by RBC was in positive ground last month as the RBC Hedge 250 Index saw its year-to-date loss expand to an estimated 4.2%. Mergers and special situations funds in particular took it on the chin, losing 3.1% in July (down 2.34% year-to-date).

Convertible arbitrage funds also took a big hit, falling 2.84% on the month (down 3.57% YTD). Other big losers included equity long/short and multi-strategy funds, with declines of 2.76% (down 3.09% YTD) and 2.52% (down 8.87% YTD), respectively. Multi-strategy funds have been the worst-performing category in the RBC index this year.

Fixed-income arbitrage was the only strategy in the black last month, according to RBC, returning 1.39% (down 0.86% YTD). Managed futures funds, despite a 1.88% drop in July, remain the best-performing strategy of the year at 9.18%. Only one other strategy, macro, is in positive ground in 2008, with a year-to-date return of 2.96% after a 1.13% decline last month.

Event-driven credit hedge funds and equity-market neutral offerings declined 2.19% (down 6.36% YTD) and 2.2% (down 1.18% YTD), respectively.