NEW YORK (Bloomberg) ? Carnival Corp. and Royal Caribbean Cruises Ltd., the world?s two biggest cruise operators, had their full-year earnings estimates reduced by Credit Suisse because weaker demand for Caribbean voyages is forcing them to cut prices for trips in the first half of 2007.

Revenue per passenger per day, or net yield, may drop for both companies in 2007, Credit Suisse analyst Scott Barry wrote yesterday in two research notes.

Reservations aren?t being booked as far in advance, he wrote. The new yield figures exclude expenses such as travel agent commissions and air fares.

The declines suggest ?extremely challenging average ticket pricing comparisons for the next several quarters at a minimum,? New York-based Barry wrote.

Both Carnival and Royal Caribbean said in the past two months demand has weakened for cruises in the Caribbean. The companies are sending vessels to other destinations including Europe to cut their reliance on island trips, which some passengers are avoiding because of last year?s hurricanes.

Shares of Carnival, the world?s largest cruise operator, fell 69 cents, or 1.8 percent, to $36.90 at 3:05 p.m. in New York Stock Exchange composite trading.

No. 2 Royal Caribbean, operator of the Royal Caribbean International and Celebrity lines, lost 76 cents, or 2.3 percent, to $32.76. Both companies are based in Miami.

?There?s a resistance to book these trips early because of hurricanes,? said Helane Becker, an analyst at Benchmark Co. in New York.

With higher airline fares and new security restrictions following last week?s arrests by UK police of 24 people for plotting to blow up airliners, ?the hassle factor is increasing.?

Carnival chief executive officer Micky Arison, 57, said in June that bookings were lowest for Caribbean cruises of three to five nights in the second half of this year.

Royal Caribbean Chief Executive Officer Richard Fain, 58, said last month reservations aren?t being made as far in advance for the Caribbean and Bermuda.

Barry lowered his profit estimate for Carnival, which operates the Holland America, Princess, Windstar and Cunard lines, to $2.68 a share from $2.74 for the fiscal year ending in November and to $2.80 from $3.05 for 2007. For Royal Caribbean, he cut his 2007 estimate to $2.80 from $2.42. He reduced his 2006 forecast for Royal Caribbean last month to $2.60.

Carnival?s stock price has dropped 31 percent this year and Royal Caribbean?s 27 percent, compared with a 1.6 percent gain in the Standard & Poor?s 500 Index.

The number of trips booked for the major cruise lines has been unchanged or down the past six weeks, Barry wrote. Checks on prices show the cost for a seven-day Caribbean cruise in 2007 has declined 10 percent to 15 percent, with lower pricing on shorter itineraries, Barry said.

US forecasters have said the 2006 Atlantic Ocean hurricane season, which began on June 1, may yield an above-average number of storms. Last year?s season set a record with 15 hurricanes, topping the 12 of 1969.

?The cruise companies lost the ability to take incremental pricing,? said Chris Scheuer, an analyst at Thrivent Investment Management in Appleton, Wisconsin, who helps oversee $67.5 billion in assets, including Carnival shares.

Barry cut the price he expects both cruise stocks to reach in the next year, lowering Carnival to $37 from $46 and Royal Caribbean to $27 from $36. He has a ?neutral? rating on both.