In a statement, the Miami-based cruise company said that nearly 6 million people cruise on the line every year, and nearly 90% of its capacity and operations are from US ports, which means incident reporting is required.
"Many of our US competitors sail from Europe and other non-US ports, so they are not mandated to submit CVSSA data as part of the reporting process," the statement said. "In essence, we report a higher number of cruise operations than others because we have a much higher percentage of US operations than others. Not because we have more incidents."
Royal Caribbean International, which reported eight sexual assault incidents this summer, compared with three a year earlier, said in a statement that the line takes every allegation seriously.
"When an incident is reported, our policy triggers immediate notification to appropriate law-enforcement authorities in compliance with mandatory reporting standards, as well as ... industry reporting guidelines," spokeswoman Melissa Charbonneau said in an email.
Both Carnival and Royal Caribbean said their security teams include many former members of law enforcement, and both cited certification by the Rape, Abuse & Incest National Network.
Despite this year's increase, the industry group Cruise Lines International Association pointed to the numbers in a larger context. About 30 million people are expected to cruise around the world this year, compared with 28.5 million last year. North America is the largest single-source market for cruise passengers.
"The latest Department of Transportation report shows that allegations of serious crime onboard cruise ships remain extremely rare, especially compared to crimes that occur on land," spokeswoman Bari Golin-Blaugrund said in an email. She pointed to a report commissioned by the group that shows crime rates on a ship are significantly lower than in a typical US city.
The report by James Alan Fox, a professor of criminology at Northeastern University, says cruising is "exceptionally safe in terms of the risks associated with violent criminal activity," especially given potential risk factors such as the number of people packed in a tight space, the number of closed areas and consumption of alcohol, according to the report.
"And, of course, the confined perimeter of a cruise ship, particularly when at sea, would make it difficult for an individual who is contemplating an aggressive act to make an escape," he wrote. "While no vacation destination is completely free of risk, cruising is clearly a relatively safe option."
Still, those who watch the cruise industry and advocate for victims of crime are pushing for higher standards. International Cruise Victims, an organization of victims and family members of those who were injured on cruises, supports new legislation filed last month that would make sure cruise lines notified the FBI within four hours of an alleged incident; report to authorities before a ship leaves a US port if an incident happened in port; report allegations to the US Consulate in the next port of call; have video surveillance equipment in all passenger common areas; and indicate whether crimes were committed against children, among other requirements.
Jim Walker, a maritime lawyer who runs the Cruise Law News blog, said in an email that the increase in crimes can be partially attributed to the rise in the number of passengers who sail. But, he said, cruise lines can still do more.
"The cruise industry has focused primarily on its PR gobbledygook ('the safety of our passengers is our number-one priority') instead of making real improvements to its shipboard security, hiring and vetting practices, and crime-prevention procedures," he said.