Pessimists are coming out of the woodwork and raising their short bets as the markets reach new highs. Exchange traded fund investors will have to keep an eye on sector plays where Wall Street is most bearish.

Short interest, the average percent of shares out on loan in the S&P index to hedge funds and other large investors, has increased over 8% in the past eight weeks, reports Lawrence Delevingne for CNBC.

“While most of the market’s recent price appreciation was seen over the last month, we’ve also seen shorts add to their positions in line with the market swell,” Simon Colvin, a Markit analyst, said in a research note.

According to Markit data, media stocks saw the largest increase in short interest – 12 of the 14 sector stocks in the S&P 500 saw an uptick in bearish bets. Cablevision Systems Corp. (NYSE: CVC) was the most-shorted media stock, with demand to borrow up over two-thirds to 12% in the past eight weeks. Gannet Co. (NYSE: GCI) and CBS Corp. (NYSE: CBS) also attracted increased short bets.

ETF investors can track the media sector through the PowerShares Dynamic Media Portfolio (NYSEArca: PBS), which includes a 4.8% weight toward CBS, 2.8% in GCI and 2.6% in CVC. PBS is down 7.5% year-to-date. [Waiting on a Discretionary Rebound]

Other areas that also attracted increased short interest include utility companies Exelon (NYSE: EXC) and Consolidated Edison (NYSE: ED), along with food retailers like Whole Foods Market (NasdaqGS: WFM).