Broker tips: Carnival, Polymetal, Tower Resources...

Investec has labelled cruise operator Carnival as a 'key sector pick', saying that the recent dip in the share price should be used as a buying opportunity; the target price is lifted from 2,500p to 3,000p."We advise utilising Friday's drop to invest in our sector key pick, with the group having: (1) an exceptional market position; (2) leading brands; (3) a resilient core customer demographic; (4) high repeat bookings; (5) emerging markets growth upside; and (6) benign industry supply growth with visibility of over four years," Hollins said.Shares of precious metals producer Polymetal International were given a lift on Monday morning by Nomura, which upgraded its rating on the stock from 'reduce' to 'buy'.The broker says that Polymetal, which listed in London in November 2011, has "slipped under the radar of institutions" during a period of negative sentiment towards precious metal miners, especially due to its complex operations and Russian exposure. "This has left Polymetal an underperformer and its valuation is undemanding," Nomura said. The stock trades at 6.2 times 2013 earnings (consensus forecasts) compared with global large-cap peers which trade on a multiple of 11.7.The target price for the shares has been cut from 1,400p to 1,340p to reflect a lower expected silver price. However the new target still suggests around 45% upside to the current share price.Jefferies has downgraded its ratings for both Tower Resources and Cove Energy as part of its review of the oil and gas exploration and production sector."We continue to favour E&Ps with high quality exploration with near-term exploration catalysts. We believe oil prices should stabilise as Saudi Arabia defends its $100/bbl target, providing a more supportive background for E&Ps."The broker's preferred exposures in the E&P sector are Tullow Oil, Ophir Energy, Falkland Oil & Gas, Chariot Oil & Gas and Bowleven. Value plays Premier Oil and Cairn Energy are expected to struggle to gain traction in this market, the broker said.BC Tullow Oil Capricorn Energy PLC Tower Resources Chariot