One of the company’s most vigorous critics, Bernstein Research’s Todd Juenger, thinks they will — or at least should. He downgraded his rating for Viacom this morning to “underperform” from “market perform” with a target price of $50 a share, below its close yesterday at $56.22. (Viacom opened this morning -2.5%.) He predicts that “MTV ratings will be down significantly” in the current fiscal year after falling 30% in the quarter that ended in September. Part of the problem is that MTV and other networks “have been starved as Viacom has funneled the majority of development dollars” into Nickelodeon — which was hit by a shocking ratings drop that began late last year. (Nick’s audience in the latest quarter was -27% vs the same period in 2011.) That’s significant because MTV’s performance could suffer later this year when the network’s hit Jersey Shore completes its final season — which follows the conclusion of another success, Teen Mom. “Looking at MTV’s 2012-13 programming lineup, it’s hard to believe there’s a high probability that any of these shows (on their own, or collectively) will offset the loss of Jersey Shore and Teen Mom 2,” Juenger says. “Returning shows like Awkward, Ridiculousness, and Teen Wolf have definitely not grabbed pop culture attention.” That could knock the wind out of MTV, which accounts for 18% of the ad sales at Viacom’s networks. Although Nickelodeon only has a few competitors, the analyst says that advertisers wanting to reach teens have “plenty of alternatives to MTV.”

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The downgrade by the prominent analyst hits as investors have begun to warm to Viacom, believing that it’s a bargain as Nickelodeon recovers from its problems. The share price is hitting record highs following a more than 20% pop since the beginning of August. That’s been fueled in part by promising ratings for the newly relaunched Teenage Mutant Ninja Turtles, which CEO Philippe Dauman considers key to the network’s turnaround.

But Juenger says that Nickelodeon isn’t out of the woods yet. He notes that Turtles is “just one show” — and a licensed one, so it “doesn’t provide evidence their internal development has developed any winners yet.” And even if ratings improve, he says, advertisers may be slow to respond.